8285932: Implementation of JEP 430 String Templates (Preview)

Reviewed-by: mcimadamore, rriggs, darcy

src/java.base/share/classes/java/lang/AbstractStringBuilder.java

@@ -1823,6 +1823,42 @@ abstract sealed class AbstractStringBuilder implements Appendable, CharSequence
         count += end - off;
     }
 
+    /**
+     * Used by StringConcatHelper via JLA. Adds the current builder count to the
+     * accumulation of items being concatenated. If the coder for the builder is
+     * UTF16 then upgrade the whole concatenation to UTF16.
+     *
+     * @param lengthCoder running accumulation of length and coder
+     *
+     * @return updated accumulation of length and coder
+     */
+    long mix(long lengthCoder) {
+        return (lengthCoder + count) | ((long)coder << 32);
+    }
+
+    /**
+     * Used by StringConcatHelper via JLA. Adds the characters in the builder value to the
+     * concatenation buffer and then updates the running accumulation of length.
+     *
+     * @param lengthCoder running accumulation of length and coder
+     * @param buffer      concatenation buffer
+     *
+     * @return running accumulation of length and coder minus the number of characters added
+     */
+    long prepend(long lengthCoder, byte[] buffer) {
+        lengthCoder -= count;
+
+        if (lengthCoder < ((long)UTF16 << 32)) {
+            System.arraycopy(value, 0, buffer, (int)lengthCoder, count);
+        } else if (coder == LATIN1) {
+            StringUTF16.inflate(value, 0, buffer, (int)lengthCoder, count);
+        } else {
+            System.arraycopy(value, 0, buffer, (int)lengthCoder << 1, count << 1);
+        }
+
+        return lengthCoder;
+    }
+
     private AbstractStringBuilder repeat(char c, int count) {
         int limit = this.count + count;
         ensureCapacityInternal(limit);

src/java.base/share/classes/java/lang/StringConcatHelper.java

@@ -26,6 +26,8 @@
 package java.lang;
 
 import jdk.internal.misc.Unsafe;
+import jdk.internal.javac.PreviewFeature;
+import jdk.internal.util.FormatConcatItem;
 import jdk.internal.vm.annotation.ForceInline;
 
 import java.lang.invoke.MethodHandle;
@@ -43,6 +45,15 @@ final class StringConcatHelper {
         // no instantiation
     }
 
+    /**
+     * Return the coder for the character.
+     * @param value character
+     * @return      coder
+     */
+    static long coder(char value) {
+        return StringLatin1.canEncode(value) ? LATIN1 : UTF16;
+    }
+
     /**
      * Check for overflow, throw exception on overflow.
      *
@@ -76,7 +87,7 @@ final class StringConcatHelper {
      * @return            new length and coder
      */
     static long mix(long lengthCoder, char value) {
-        return checkOverflow(lengthCoder + 1) | (StringLatin1.canEncode(value) ? 0 : UTF16);
+        return checkOverflow(lengthCoder + 1) | coder(value);
     }
 
     /**
@@ -116,6 +127,21 @@ final class StringConcatHelper {
         return checkOverflow(lengthCoder);
     }
 
+    /**
+     * Mix value length and coder into current length and coder.
+     * @param lengthCoder String length with coder packed into higher bits
+     *                    the upper word.
+     * @param value       value to mix in
+     * @return            new length and coder
+     * @since 21
+     */
+    @PreviewFeature(feature=PreviewFeature.Feature.STRING_TEMPLATES)
+    static long mix(long lengthCoder, FormatConcatItem value) {
+        lengthCoder = value.mix(lengthCoder);
+
+        return checkOverflow(lengthCoder);
+    }
+
     /**
      * Prepends the stringly representation of boolean value into buffer,
      * given the coder and final index. Index is measured in chars, not in bytes!
@@ -319,6 +345,49 @@ final class StringConcatHelper {
         return indexCoder;
     }
 
+    /**
+     * Prepends the stringly representation of FormatConcatItem value into buffer,
+     * given the coder and final index. Index is measured in chars, not in bytes!
+     *
+     * @param indexCoder final char index in the buffer, along with coder packed
+     *                   into higher bits.
+     * @param buf        buffer to append to
+     * @param value      String value to encode
+     * @return           updated index (coder value retained)
+     * @since 21
+     */
+    @PreviewFeature(feature=PreviewFeature.Feature.STRING_TEMPLATES)
+    private static long prepend(long indexCoder, byte[] buf,
+                                FormatConcatItem value) {
+        try {
+            return value.prepend(indexCoder, buf);
+        } catch (Error ex) {
+            throw ex;
+        } catch (Throwable ex) {
+            throw new AssertionError("FormatConcatItem prepend error", ex);
+        }
+    }
+
+    /**
+     * Prepends constant and the stringly representation of value into buffer,
+     * given the coder and final index. Index is measured in chars, not in bytes!
+     *
+     * @param indexCoder final char index in the buffer, along with coder packed
+     *                   into higher bits.
+     * @param buf        buffer to append to
+     * @param value      boolean value to encode
+     * @param prefix     a constant to prepend before value
+     * @return           updated index (coder value retained)
+     * @since 21
+     */
+    @PreviewFeature(feature=PreviewFeature.Feature.STRING_TEMPLATES)
+    static long prepend(long indexCoder, byte[] buf,
+                        FormatConcatItem value, String prefix) {
+        indexCoder = prepend(indexCoder, buf, value);
+        if (prefix != null) indexCoder = prepend(indexCoder, buf, prefix);
+        return indexCoder;
+    }
+
     /**
      * Instantiates the String with given buffer and coder
      * @param buf           buffer to use
@@ -332,7 +401,8 @@ final class StringConcatHelper {
         } else if (indexCoder == UTF16) {
             return new String(buf, String.UTF16);
         } else {
-            throw new InternalError("Storage is not completely initialized, " + (int)indexCoder + " bytes left");
+            throw new InternalError("Storage is not completely initialized, " +
+                    (int)indexCoder + " bytes left");
         }
     }
 
@@ -449,6 +519,71 @@ final class StringConcatHelper {
         return String.COMPACT_STRINGS ? LATIN1 : UTF16;
     }
 
+    /*
+     * Initialize after phase1.
+     */
+    private static class LateInit {
+        static final MethodHandle GETCHAR_LATIN1_MH;
+
+        static final MethodHandle GETCHAR_UTF16_MH;
+
+        static final MethodHandle PUTCHAR_LATIN1_MH;
+
+        static final MethodHandle PUTCHAR_UTF16_MH;
+
+        static {
+            MethodType getCharMT =
+                MethodType.methodType(char.class,
+                        byte[].class, int.class);
+            MethodType putCharMT =
+                MethodType.methodType(void.class,
+                        byte[].class, int.class, int.class);
+            GETCHAR_LATIN1_MH = lookupStatic("getCharLatin1", getCharMT);
+            GETCHAR_UTF16_MH = lookupStatic("getCharUTF16", getCharMT);
+            PUTCHAR_LATIN1_MH = lookupStatic("putCharLatin1", putCharMT);
+            PUTCHAR_UTF16_MH = lookupStatic("putCharUTF16", putCharMT);
+        }
+
+    }
+
+    @ForceInline
+    @PreviewFeature(feature=PreviewFeature.Feature.STRING_TEMPLATES)
+    static char getCharLatin1(byte[] buffer, int index) {
+        return (char)buffer[index];
+    }
+
+    @ForceInline
+    @PreviewFeature(feature=PreviewFeature.Feature.STRING_TEMPLATES)
+    static char getCharUTF16(byte[] buffer, int index) {
+        return StringUTF16.getChar(buffer, index);
+    }
+
+    @ForceInline
+    @PreviewFeature(feature=PreviewFeature.Feature.STRING_TEMPLATES)
+    static void putCharLatin1(byte[] buffer, int index, int ch) {
+        buffer[index] = (byte)ch;
+    }
+
+    @ForceInline
+    @PreviewFeature(feature=PreviewFeature.Feature.STRING_TEMPLATES)
+    static void putCharUTF16(byte[] buffer, int index, int ch) {
+        StringUTF16.putChar(buffer, index, ch);
+    }
+
+    @ForceInline
+    @PreviewFeature(feature=PreviewFeature.Feature.STRING_TEMPLATES)
+    static MethodHandle selectGetChar(long indexCoder) {
+        return indexCoder < UTF16 ? LateInit.GETCHAR_LATIN1_MH :
+                                    LateInit.GETCHAR_UTF16_MH;
+    }
+
+    @ForceInline
+    @PreviewFeature(feature=PreviewFeature.Feature.STRING_TEMPLATES)
+    static MethodHandle selectPutChar(long indexCoder) {
+        return indexCoder < UTF16 ? LateInit.PUTCHAR_LATIN1_MH :
+                                    LateInit.PUTCHAR_UTF16_MH;
+    }
+
     static MethodHandle lookupStatic(String name, MethodType methodType) {
         try {
             return MethodHandles.lookup().findStatic(StringConcatHelper.class, name, methodType);

src/java.base/share/classes/java/lang/StringTemplate.java

@@ -0,0 +1,621 @@
+/*
+ * Copyright (c) 2023, Oracle and/or its affiliates. All rights reserved.
+ * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
+ *
+ * This code is free software; you can redistribute it and/or modify it
+ * under the terms of the GNU General Public License version 2 only, as
+ * published by the Free Software Foundation.  Oracle designates this
+ * particular file as subject to the "Classpath" exception as provided
+ * by Oracle in the LICENSE file that accompanied this code.
+ *
+ * This code is distributed in the hope that it will be useful, but WITHOUT
+ * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
+ * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
+ * version 2 for more details (a copy is included in the LICENSE file that
+ * accompanied this code).
+ *
+ * You should have received a copy of the GNU General Public License version
+ * 2 along with this work; if not, write to the Free Software Foundation,
+ * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
+ *
+ * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
+ * or visit www.oracle.com if you need additional information or have any
+ * questions.
+ */
+
+package java.lang;
+
+import java.lang.invoke.MethodHandle;
+import java.lang.invoke.MethodType;
+import java.util.FormatProcessor;
+import java.util.function.Function;
+import java.util.List;
+import java.util.Objects;
+
+import jdk.internal.access.JavaTemplateAccess;
+import jdk.internal.access.SharedSecrets;
+import jdk.internal.javac.PreviewFeature;
+
+/**
+ * {@link StringTemplate} is the run-time representation of a string template or
+ * text block template in a template expression.
+ * <p>
+ * In the source code of a Java program, a string template or text block template
+ * contains an interleaved succession of <em>fragment literals</em> and <em>embedded
+ * expressions</em>. The {@link StringTemplate#fragments()} method returns the
+ * fragment literals, and the {@link StringTemplate#values()} method returns the
+ * results of evaluating the embedded expressions. {@link StringTemplate} does not
+ * provide access to the source code of the embedded expressions themselves; it is
+ * not a compile-time representation of a string template or text block template.
+ * <p>
+ * {@link StringTemplate} is primarily used in conjunction with a template processor
+ * to produce a string or other meaningful value. Evaluation of a template expression
+ * first produces an instance of {@link StringTemplate}, representing the right hand side
+ * of the template expression, and then passes the instance to the template processor
+ * given by the template expression.
+ * <p>
+ * For example, the following code contains a template expression that uses the template
+ * processor {@code RAW}, which simply yields the {@link StringTemplate} passed to it:
+ * {@snippet :
+ * int x = 10;
+ * int y = 20;
+ * StringTemplate st = RAW."\{x} + \{y} = \{x + y}";
+ * List<String> fragments = st.fragments();
+ * List<Object> values = st.values();
+ * }
+ * {@code fragments} will be equivalent to {@code List.of("", " + ", " = ", "")},
+ * which includes the empty first and last fragments. {@code values} will be the
+ * equivalent of {@code List.of(10, 20, 30)}.
+ * <p>
+ * The following code contains a template expression with the same template but with a
+ * different template processor, {@code STR}:
+ * {@snippet :
+ * int x = 10;
+ * int y = 20;
+ * String s = STR."\{x} + \{y} = \{x + y}";
+ * }
+ * When the template expression is evaluated, an instance of {@link StringTemplate} is
+ * produced that returns the same lists from {@link StringTemplate#fragments()} and
+ * {@link StringTemplate#values()} as shown above. The {@link StringTemplate#STR} template
+ * processor uses these lists to yield an interpolated string. The value of {@code s} will
+ * be equivalent to {@code "10 + 20 = 30"}.
+ * <p>
+ * The {@code interpolate()} method provides a direct way to perform string interpolation
+ * of a {@link StringTemplate}. Template processors can use the following code pattern:
+ * {@snippet :
+ * List<String> fragments = st.fragments();
+ * List<Object> values    = st.values();
+ * ... check or manipulate the fragments and/or values ...
+ * String result = StringTemplate.interpolate(fragments, values);
+ * }
+ * The {@link StringTemplate#process(Processor)} method, in conjunction with
+ * the {@link StringTemplate#RAW} processor, may be used to defer processing of a
+ * {@link StringTemplate}.
+ * {@snippet :
+ * StringTemplate st = RAW."\{x} + \{y} = \{x + y}";
+ * ...other steps...
+ * String result = st.process(STR);
+ * }
+ * The factory methods {@link StringTemplate#of(String)} and
+ * {@link StringTemplate#of(List, List)} can be used to construct a {@link StringTemplate}.
+ *
+ * @see Processor
+ * @see java.util.FormatProcessor
+ *
+ * @implNote Implementations of {@link StringTemplate} must minimally implement the
+ * methods {@link StringTemplate#fragments()} and {@link StringTemplate#values()}.
+ * Instances of {@link StringTemplate} are considered immutable. To preserve the
+ * semantics of string templates and text block templates, the list returned by
+ * {@link StringTemplate#fragments()} must be one element larger than the list returned
+ * by {@link StringTemplate#values()}.
+ *
+ * @since 21
+ *
+ * @jls 15.8.6 Process Template Expressions
+ */
+@PreviewFeature(feature=PreviewFeature.Feature.STRING_TEMPLATES)
+public interface StringTemplate {
+    /**
+     * Returns a list of fragment literals for this {@link StringTemplate}.
+     * The fragment literals are the character sequences preceding each of the embedded
+     * expressions in source code, plus the character sequence following the last
+     * embedded expression. Such character sequences may be zero-length if an embedded
+     * expression appears at the beginning or end of a template, or if two embedded
+     * expressions are directly adjacent in a template.
+     * In the example: {@snippet :
+     * String student = "Mary";
+     * String teacher = "Johnson";
+     * StringTemplate st = RAW."The student \{student} is in \{teacher}'s classroom.";
+     * List<String> fragments = st.fragments(); // @highlight substring="fragments()"
+     * }
+     * {@code fragments} will be equivalent to
+     * {@code List.of("The student ", " is in ", "'s classroom.")}
+     *
+     * @return list of string fragments
+     *
+     * @implSpec the list returned is immutable
+     */
+    List<String> fragments();
+
+    /**
+     * Returns a list of embedded expression results for this {@link StringTemplate}.
+     * In the example:
+     * {@snippet :
+     * String student = "Mary";
+     * String teacher = "Johnson";
+     * StringTemplate st = RAW."The student \{student} is in \{teacher}'s classroom.";
+     * List<Object> values = st.values(); // @highlight substring="values()"
+     * }
+     * {@code values} will be equivalent to {@code List.of(student, teacher)}
+     *
+     * @return list of expression values
+     *
+     * @implSpec the list returned is immutable
+     */
+    List<Object> values();
+
+    /**
+     * Returns the string interpolation of the fragments and values for this
+     * {@link StringTemplate}.
+     * @apiNote For better visibility and when practical, it is recommended to use the
+     * {@link StringTemplate#STR} processor instead of invoking the
+     * {@link StringTemplate#interpolate()} method.
+     * {@snippet :
+     * String student = "Mary";
+     * String teacher = "Johnson";
+     * StringTemplate st = RAW."The student \{student} is in \{teacher}'s classroom.";
+     * String result = st.interpolate(); // @highlight substring="interpolate()"
+     * }
+     * In the above example, the value of  {@code result} will be
+     * {@code "The student Mary is in Johnson's classroom."}. This is
+     * produced by the interleaving concatenation of fragments and values from the supplied
+     * {@link StringTemplate}. To accommodate concatenation, values are converted to strings
+     * as if invoking {@link String#valueOf(Object)}.
+     *
+     * @return interpolation of this {@link StringTemplate}
+     *
+     * @implSpec The default implementation returns the result of invoking
+     * {@code StringTemplate.interpolate(this.fragments(), this.values())}.
+     */
+    default String interpolate() {
+        return StringTemplate.interpolate(fragments(), values());
+    }
+
+    /**
+     * Returns the result of applying the specified processor to this {@link StringTemplate}.
+     * This method can be used as an alternative to string template expressions. For example,
+     * {@snippet :
+     * String student = "Mary";
+     * String teacher = "Johnson";
+     * String result1 = STR."The student \{student} is in \{teacher}'s classroom.";
+     * String result2 = RAW."The student \{student} is in \{teacher}'s classroom.".process(STR); // @highlight substring="process"
+     * }
+     * Produces an equivalent result for both {@code result1} and {@code result2}.
+     *
+     * @param processor the {@link Processor} instance to process
+     *
+     * @param <R>  Processor's process result type.
+     * @param <E>  Exception thrown type.
+     *
+     * @return constructed object of type {@code R}
+     *
+     * @throws E exception thrown by the template processor when validation fails
+     * @throws NullPointerException if processor is null
+     *
+     * @implSpec The default implementation returns the result of invoking
+     * {@code processor.process(this)}. If the invocation throws an exception that
+     * exception is forwarded to the caller.
+     */
+    default <R, E extends Throwable> R
+    process(Processor<? extends R, ? extends E> processor) throws E {
+        Objects.requireNonNull(processor, "processor should not be null");
+
+        return processor.process(this);
+    }
+
+    /**
+     * Produces a diagnostic string that describes the fragments and values of the supplied
+     * {@link StringTemplate}.
+     *
+     * @param stringTemplate  the {@link StringTemplate} to represent
+     *
+     * @return diagnostic string representing the supplied string template
+     *
+     * @throws NullPointerException if stringTemplate is null
+     */
+    static String toString(StringTemplate stringTemplate) {
+        Objects.requireNonNull(stringTemplate, "stringTemplate should not be null");
+        return "StringTemplate{ fragments = [ \"" +
+                String.join("\", \"", stringTemplate.fragments()) +
+                "\" ], values = " +
+                stringTemplate.values() +
+                " }";
+    }
+
+    /**
+     * Returns a {@link StringTemplate} as if constructed by invoking
+     * {@code StringTemplate.of(List.of(string), List.of())}. That is, a {@link StringTemplate}
+     * with one fragment and no values.
+     *
+     * @param string  single string fragment
+     *
+     * @return StringTemplate composed from string
+     *
+     * @throws NullPointerException if string is null
+     */
+    static StringTemplate of(String string) {
+        Objects.requireNonNull(string, "string must not be null");
+        JavaTemplateAccess JTA = SharedSecrets.getJavaTemplateAccess();
+        return JTA.of(List.of(string), List.of());
+    }
+
+    /**
+     * Returns a StringTemplate with the given fragments and values.
+     *
+     * @implSpec The {@code fragments} list size must be one more that the
+     * {@code values} list size.
+     *
+     * @param fragments list of string fragments
+     * @param values    list of expression values
+     *
+     * @return StringTemplate composed from string
+     *
+     * @throws IllegalArgumentException if fragments list size is not one more
+     *         than values list size
+     * @throws NullPointerException if fragments is null or values is null or if any fragment is null.
+     *
+     * @implNote Contents of both lists are copied to construct immutable lists.
+     */
+    static StringTemplate of(List<String> fragments, List<?> values) {
+        Objects.requireNonNull(fragments, "fragments must not be null");
+        Objects.requireNonNull(values, "values must not be null");
+        if (values.size() + 1 != fragments.size()) {
+            throw new IllegalArgumentException(
+                    "fragments list size is not one more than values list size");
+        }
+        JavaTemplateAccess JTA = SharedSecrets.getJavaTemplateAccess();
+        return JTA.of(fragments, values);
+    }
+
+    /**
+     * Creates a string that interleaves the elements of values between the
+     * elements of fragments. To accommodate interpolation, values are converted to strings
+     * as if invoking {@link String#valueOf(Object)}.
+     *
+     * @param fragments  list of String fragments
+     * @param values     list of expression values
+     *
+     * @return String interpolation of fragments and values
+     *
+     * @throws IllegalArgumentException if fragments list size is not one more
+     *         than values list size
+     * @throws NullPointerException fragments or values is null or if any of the fragments is null
+     */
+    static String interpolate(List<String> fragments, List<?> values) {
+        Objects.requireNonNull(fragments, "fragments must not be null");
+        Objects.requireNonNull(values, "values must not be null");
+        int fragmentsSize = fragments.size();
+        int valuesSize = values.size();
+        if (fragmentsSize != valuesSize + 1) {
+            throw new IllegalArgumentException("fragments must have one more element than values");
+        }
+        JavaTemplateAccess JTA = SharedSecrets.getJavaTemplateAccess();
+        return JTA.interpolate(fragments, values);
+    }
+
+    /**
+     * Combine zero or more {@link StringTemplate StringTemplates} into a single
+     * {@link StringTemplate}.
+     * {@snippet :
+     * StringTemplate st = StringTemplate.combine(RAW."\{a}", RAW."\{b}", RAW."\{c}");
+     * assert st.interpolate().equals(STR."\{a}\{b}\{c}");
+     * }
+     * Fragment lists from the {@link StringTemplate StringTemplates} are combined end to
+     * end with the last fragment from each {@link StringTemplate} concatenated with the
+     * first fragment of the next. To demonstrate, if we were to take two strings and we
+     * combined them as follows: {@snippet lang = "java":
+     * String s1 = "abc";
+     * String s2 = "xyz";
+     * String sc = s1 + s2;
+     * assert Objects.equals(sc, "abcxyz");
+     * }
+     * the last character {@code "c"} from the first string is juxtaposed with the first
+     * character {@code "x"} of the second string. The same would be true of combining
+     * {@link StringTemplate StringTemplates}.
+     * {@snippet lang ="java":
+     * StringTemplate st1 = RAW."a\{}b\{}c";
+     * StringTemplate st2 = RAW."x\{}y\{}z";
+     * StringTemplate st3 = RAW."a\{}b\{}cx\{}y\{}z";
+     * StringTemplate stc = StringTemplate.combine(st1, st2);
+     *
+     * assert Objects.equals(st1.fragments(), List.of("a", "b", "c"));
+     * assert Objects.equals(st2.fragments(), List.of("x", "y", "z"));
+     * assert Objects.equals(st3.fragments(), List.of("a", "b", "cx", "y", "z"));
+     * assert Objects.equals(stc.fragments(), List.of("a", "b", "cx", "y", "z"));
+     * }
+     * Values lists are simply concatenated to produce a single values list.
+     * The result is a well-formed {@link StringTemplate} with n+1 fragments and n values, where
+     * n is the total of number of values across all the supplied
+     * {@link StringTemplate StringTemplates}.
+     *
+     * @param stringTemplates  zero or more {@link StringTemplate}
+     *
+     * @return combined {@link StringTemplate}
+     *
+     * @throws NullPointerException if stringTemplates is null or if any of the
+     * {@code stringTemplates} are null
+     *
+     * @implNote If zero {@link StringTemplate} arguments are provided then a
+     * {@link StringTemplate} with an empty fragment and no values is returned, as if invoking
+     * <code>StringTemplate.of("")</code> . If only one {@link StringTemplate} argument is provided
+     * then it is returned unchanged.
+     */
+    static StringTemplate combine(StringTemplate... stringTemplates) {
+        JavaTemplateAccess JTA = SharedSecrets.getJavaTemplateAccess();
+        return JTA.combine(stringTemplates);
+    }
+
+    /**
+     * Combine a list of {@link StringTemplate StringTemplates} into a single
+     * {@link StringTemplate}.
+     * {@snippet :
+     * StringTemplate st = StringTemplate.combine(List.of(RAW."\{a}", RAW."\{b}", RAW."\{c}"));
+     * assert st.interpolate().equals(STR."\{a}\{b}\{c}");
+     * }
+     * Fragment lists from the {@link StringTemplate StringTemplates} are combined end to
+     * end with the last fragment from each {@link StringTemplate} concatenated with the
+     * first fragment of the next. To demonstrate, if we were to take two strings and we
+     * combined them as follows: {@snippet lang = "java":
+     * String s1 = "abc";
+     * String s2 = "xyz";
+     * String sc = s1 + s2;
+     * assert Objects.equals(sc, "abcxyz");
+     * }
+     * the last character {@code "c"} from the first string is juxtaposed with the first
+     * character {@code "x"} of the second string. The same would be true of combining
+     * {@link StringTemplate StringTemplates}.
+     * {@snippet lang ="java":
+     * StringTemplate st1 = RAW."a\{}b\{}c";
+     * StringTemplate st2 = RAW."x\{}y\{}z";
+     * StringTemplate st3 = RAW."a\{}b\{}cx\{}y\{}z";
+     * StringTemplate stc = StringTemplate.combine(List.of(st1, st2));
+     *
+     * assert Objects.equals(st1.fragments(), List.of("a", "b", "c"));
+     * assert Objects.equals(st2.fragments(), List.of("x", "y", "z"));
+     * assert Objects.equals(st3.fragments(), List.of("a", "b", "cx", "y", "z"));
+     * assert Objects.equals(stc.fragments(), List.of("a", "b", "cx", "y", "z"));
+     * }
+     * Values lists are simply concatenated to produce a single values list.
+     * The result is a well-formed {@link StringTemplate} with n+1 fragments and n values, where
+     * n is the total of number of values across all the supplied
+     * {@link StringTemplate StringTemplates}.
+     *
+     * @param stringTemplates  list of {@link StringTemplate}
+     *
+     * @return combined {@link StringTemplate}
+     *
+     * @throws NullPointerException if stringTemplates is null or if any of the
+     * its elements are null
+     *
+     * @implNote If {@code stringTemplates.size() == 0} then a {@link StringTemplate} with
+     * an empty fragment and no values is returned, as if invoking
+     * <code>StringTemplate.of("")</code> . If {@code stringTemplates.size() == 1}
+     * then the first element of the list is returned unchanged.
+     */
+    static StringTemplate combine(List<StringTemplate> stringTemplates) {
+        JavaTemplateAccess JTA = SharedSecrets.getJavaTemplateAccess();
+        return JTA.combine(stringTemplates.toArray(new StringTemplate[0]));
+    }
+
+    /**
+     * This {@link Processor} instance is conventionally used for the string interpolation
+     * of a supplied {@link StringTemplate}.
+     * <p>
+     * For better visibility and when practical, it is recommended that users use the
+     * {@link StringTemplate#STR} processor instead of invoking the
+     * {@link StringTemplate#interpolate()} method.
+     * Example: {@snippet :
+     * int x = 10;
+     * int y = 20;
+     * String result = STR."\{x} + \{y} = \{x + y}"; // @highlight substring="STR"
+     * }
+     * In the above example, the value of {@code result} will be {@code "10 + 20 = 30"}. This is
+     * produced by the interleaving concatenation of fragments and values from the supplied
+     * {@link StringTemplate}. To accommodate concatenation, values are converted to strings
+     * as if invoking {@link String#valueOf(Object)}.
+     * @apiNote {@link StringTemplate#STR} is statically imported implicitly into every
+     * Java compilation unit.
+     */
+    Processor<String, RuntimeException> STR = StringTemplate::interpolate;
+
+    /**
+     * This {@link Processor} instance is conventionally used to indicate that the
+     * processing of the {@link StringTemplate} is to be deferred to a later time. Deferred
+     * processing can be resumed by invoking the
+     * {@link StringTemplate#process(Processor)} or
+     * {@link Processor#process(StringTemplate)} methods.
+     * {@snippet :
+     * import static java.lang.StringTemplate.RAW;
+     * ...
+     * StringTemplate st = RAW."\{x} + \{y} = \{x + y}";
+     * ...other steps...
+     * String result = STR.process(st);
+     * }
+     * @implNote Unlike {@link StringTemplate#STR}, {@link StringTemplate#RAW} must be
+     * statically imported explicitly.
+     */
+    Processor<StringTemplate, RuntimeException> RAW = st -> st;
+
+    /**
+     * This interface describes the methods provided by a generalized string template processor. The
+     * primary method {@link Processor#process(StringTemplate)} is used to validate
+     * and compose a result using a {@link StringTemplate StringTemplate's} fragments and values lists.
+     * <p>
+     * For example:
+     * {@snippet :
+     * class MyProcessor implements Processor<String, IllegalArgumentException> {
+     *     @Override
+     *     public String process(StringTemplate st) throws IllegalArgumentException {
+     *          StringBuilder sb = new StringBuilder();
+     *          Iterator<String> fragmentsIter = st.fragments().iterator();
+     *
+     *          for (Object value : st.values()) {
+     *              sb.append(fragmentsIter.next());
+     *
+     *              if (value instanceof Boolean) {
+     *                  throw new IllegalArgumentException("I don't like Booleans");
+     *              }
+     *
+     *              sb.append(value);
+     *          }
+     *
+     *          sb.append(fragmentsIter.next());
+     *
+     *          return sb.toString();
+     *     }
+     * }
+     *
+     * MyProcessor myProcessor = new MyProcessor();
+     * try {
+     *     int x = 10;
+     *     int y = 20;
+     *     String result = myProcessor."\{x} + \{y} = \{x + y}";
+     *     ...
+     * } catch (IllegalArgumentException ex) {
+     *     ...
+     * }
+     * }
+     * Implementations of this interface may provide, but are not limited to, validating
+     * inputs, composing inputs into a result, and transforming an intermediate string
+     * result to a non-string value before delivering the final result.
+     * <p>
+     * The user has the option of validating inputs used in composition. For example an SQL
+     * processor could prevent injection vulnerabilities by sanitizing inputs or throwing an
+     * exception of type {@code E} if an SQL statement is a potential vulnerability.
+     * <p>
+     * Composing allows user control over how the result is assembled. Most often, a
+     * user will construct a new string from the string template, with placeholders
+     * replaced by string representations of value list elements. These string
+     * representations are created as if invoking {@link String#valueOf}.
+     * <p>
+     * Transforming allows the processor to return something other than a string. For
+     * instance, a JSON processor could return a JSON object, by parsing the string created
+     * by composition, instead of the composed string.
+     * <p>
+     * {@link Processor} is a {@link FunctionalInterface}. This permits
+     * declaration of a processor using lambda expressions;
+     * {@snippet :
+     * Processor<String, RuntimeException> processor = st -> {
+     *     List<String> fragments = st.fragments();
+     *     List<Object> values = st.values();
+     *     // check or manipulate the fragments and/or values
+     *     ...
+     *     return StringTemplate.interpolate(fragments, values);
+     * };
+     * }
+     * The {@link StringTemplate#interpolate()} method is available for those processors
+     * that just need to work with the string interpolation;
+     * {@snippet :
+     * Processor<String, RuntimeException> processor = StringTemplate::interpolate;
+     * }
+     * or simply transform the string interpolation into something other than
+     * {@link String};
+     * {@snippet :
+     * Processor<JSONObject, RuntimeException> jsonProcessor = st -> new JSONObject(st.interpolate());
+     * }
+     * @implNote The Java compiler automatically imports {@link StringTemplate#STR}
+     *
+     * @param <R>  Processor's process result type
+     * @param <E>  Exception thrown type
+     *
+     * @see StringTemplate
+     * @see java.util.FormatProcessor
+     *
+     * @since 21
+     *
+     * @jls 15.8.6 Process Template Expressions
+     */
+    @PreviewFeature(feature=PreviewFeature.Feature.STRING_TEMPLATES)
+    @FunctionalInterface
+    public interface Processor<R, E extends Throwable> {
+
+        /**
+         * Constructs a result based on the template fragments and values in the
+         * supplied {@link StringTemplate stringTemplate} object.
+         * @apiNote Processing of a {@link StringTemplate} may include validation according to the particular facts relating
+         * to each situation. The {@code E} type parameter indicates the type of checked exception that is thrown by
+         * {@link #process} if validation fails, ex. {@code java.sql.SQLException}. If no checked exception is expected
+         * then {@link RuntimeException} may be used. Note that unchecked exceptions, such as {@link RuntimeException},
+         * {@link NullPointerException} or {@link IllegalArgumentException} may be thrown as part of the normal
+         * method arguments processing. Details of which exceptions are thrown will be found in the documentation
+         * of the specific implementation.
+         *
+         * @param stringTemplate  a {@link StringTemplate} instance
+         *
+         * @return constructed object of type R
+         *
+         * @throws E exception thrown by the template processor when validation fails
+         */
+        R process(StringTemplate stringTemplate) throws E;
+
+        /**
+         * This factory method can be used to create a {@link Processor} containing a
+         * {@link Processor#process} method derived from a lambda expression. As an example;
+         * {@snippet :
+         * Processor<String, RuntimeException> mySTR = Processor.of(StringTemplate::interpolate);
+         * int x = 10;
+         * int y = 20;
+         * String str = mySTR."\{x} + \{y} = \{x + y}";
+         * }
+         * The result type of the constructed {@link Processor} may be derived from
+         * the lambda expression, thus this method may be used in a var
+         * statement. For example, {@code mySTR} from above can also be declared using;
+         * {@snippet :
+         * var mySTR = Processor.of(StringTemplate::interpolate);
+         * }
+         * {@link RuntimeException} is the assumed exception thrown type.
+         *
+         * @param process a function that takes a {@link StringTemplate} as an argument
+         *                and returns the inferred result type
+         *
+         * @return a {@link Processor}
+         *
+         * @param <T>  Processor's process result type
+         */
+        static <T> Processor<T, RuntimeException> of(Function<? super StringTemplate, ? extends T> process) {
+            return process::apply;
+        }
+
+        /**
+         * Built-in policies using this additional interface have the flexibility to
+         * specialize the composition of the templated string by returning a customized
+         * {@link MethodHandle} from {@link Linkage#linkage linkage}.
+         * These specializations are typically implemented to improve performance;
+         * specializing value types or avoiding boxing and vararg arrays.
+         *
+         * @implNote This interface is sealed to only allow standard processors.
+         *
+         * @since 21
+         */
+        @PreviewFeature(feature=PreviewFeature.Feature.STRING_TEMPLATES)
+        public sealed interface Linkage permits FormatProcessor {
+            /**
+             * This method creates a {@link MethodHandle} that when invoked with arguments of
+             * those specified in {@code type} returns a result that equals that returned by
+             * the template processor's process method. The difference being that this method
+             * can preview the template's fragments and value types in advance of usage and
+             * thereby has the opportunity to produce a specialized implementation.
+             *
+             * @param fragments  string template fragments
+             * @param type       method type, includes the StringTemplate receiver as
+             * well as the value types
+             *
+             * @return {@link MethodHandle} for the processor applied to template
+             *
+             * @throws NullPointerException if any of the arguments are null
+             */
+            MethodHandle linkage(List<String> fragments, MethodType type);
+        }
+    }
+
+}

src/java.base/share/classes/java/lang/System.java

@@ -77,10 +77,11 @@ import jdk.internal.reflect.CallerSensitive;
 import jdk.internal.reflect.Reflection;
 import jdk.internal.access.JavaLangAccess;
 import jdk.internal.access.SharedSecrets;
-import jdk.internal.misc.VM;
+import jdk.internal.javac.PreviewFeature;
 import jdk.internal.logger.LoggerFinderLoader;
 import jdk.internal.logger.LazyLoggers;
 import jdk.internal.logger.LocalizedLoggerWrapper;
+import jdk.internal.misc.VM;
 import jdk.internal.util.SystemProps;
 import jdk.internal.vm.Continuation;
 import jdk.internal.vm.ContinuationScope;
@@ -2522,6 +2523,23 @@ public final class System {
                 return StringConcatHelper.mix(lengthCoder, constant);
             }
 
+            @PreviewFeature(feature=PreviewFeature.Feature.STRING_TEMPLATES)
+            public long stringConcatCoder(char value) {
+                return StringConcatHelper.coder(value);
+            }
+
+            @PreviewFeature(feature=PreviewFeature.Feature.STRING_TEMPLATES)
+            public long stringBuilderConcatMix(long lengthCoder,
+                                               StringBuilder sb) {
+                return sb.mix(lengthCoder);
+            }
+
+            @PreviewFeature(feature=PreviewFeature.Feature.STRING_TEMPLATES)
+            public long stringBuilderConcatPrepend(long lengthCoder, byte[] buf,
+                                                   StringBuilder sb) {
+                return sb.prepend(lengthCoder, buf);
+            }
+
             public String join(String prefix, String suffix, String delimiter, String[] elements, int size) {
                 return String.join(prefix, suffix, delimiter, elements, size);
             }

src/java.base/share/classes/java/lang/invoke/StringConcatFactory.java

@@ -27,10 +27,15 @@ package java.lang.invoke;
 
 import jdk.internal.access.JavaLangAccess;
 import jdk.internal.access.SharedSecrets;
+import jdk.internal.javac.PreviewFeature;
+import jdk.internal.util.FormatConcatItem;
 import jdk.internal.vm.annotation.Stable;
 import sun.invoke.util.Wrapper;
 
 import java.lang.invoke.MethodHandles.Lookup;
+import java.util.ArrayList;
+import java.util.Iterator;
+import java.util.List;
 import java.util.Objects;
 
 import static java.lang.invoke.MethodType.methodType;
@@ -110,8 +115,14 @@ public final class StringConcatFactory {
      * While the maximum number of argument slots that indy call can handle is 253,
      * we do not use all those slots, to let the strategies with MethodHandle
      * combinators to use some arguments.
+     *
+     * @since 21
      */
-    private static final int MAX_INDY_CONCAT_ARG_SLOTS = 200;
+    @PreviewFeature(feature=PreviewFeature.Feature.STRING_TEMPLATES)
+    public static final int MAX_INDY_CONCAT_ARG_SLOTS;
+    // Use static initialize block to avoid MAX_INDY_CONCAT_ARG_SLOTS being treating
+    // as a constant for constant folding.
+    static { MAX_INDY_CONCAT_ARG_SLOTS = 200; }
 
     private static final JavaLangAccess JLA = SharedSecrets.getJavaLangAccess();
 
@@ -321,6 +332,7 @@ public final class StringConcatFactory {
     {
         Objects.requireNonNull(lookup, "Lookup is null");
         Objects.requireNonNull(name, "Name is null");
+        Objects.requireNonNull(recipe, "Recipe is null");
         Objects.requireNonNull(concatType, "Concat type is null");
         Objects.requireNonNull(constants, "Constants are null");
 
@@ -488,14 +500,12 @@ public final class StringConcatFactory {
             // Use int as the logical type for subword integral types
             // (byte and short). char and boolean require special
             // handling so don't change the logical type of those
-            if (cl == byte.class || cl == short.class) {
+            ptypes[i] = promoteToIntType(ptypes[i]);
-                ptypes[i] = int.class;
-            }
             // Object, float and double will be eagerly transformed
             // into a (non-null) String as a first step after invocation.
             // Set up to use String as the logical type for such arguments
             // internally.
-            else if (cl == Object.class) {
+            if (cl == Object.class) {
                 if (objFilters == null) {
                     objFilters = new MethodHandle[ptypes.length];
                 }
@@ -664,7 +674,6 @@ public final class StringConcatFactory {
         return argPositions;
     }
 
-
     private static MethodHandle foldInLastMixers(MethodHandle mh, long initialLengthCoder, int pos, Class<?>[] ptypes, int count) {
         MethodHandle mix = switch (count) {
             case 1 -> mixer(ptypes[pos]);
@@ -710,6 +719,9 @@ public final class StringConcatFactory {
         int idx = classIndex(cl);
         MethodHandle prepend = PREPENDERS[idx];
         if (prepend == null) {
+            if (idx == STRING_CONCAT_ITEM) {
+                cl = FormatConcatItem.class;
+            }
             PREPENDERS[idx] = prepend = JLA.stringConcatHelper("prepend",
                     methodType(long.class, long.class, byte[].class,
                             Wrapper.asPrimitiveType(cl), String.class)).rebind();
@@ -722,13 +734,15 @@ public final class StringConcatFactory {
             LONG_IDX = 2,
             BOOLEAN_IDX = 3,
             STRING_IDX = 4,
-            TYPE_COUNT = 5;
+            STRING_CONCAT_ITEM = 5,
+            TYPE_COUNT = 6;
     private static int classIndex(Class<?> cl) {
-        if (cl == String.class)  return STRING_IDX;
+        if (cl == String.class)                          return STRING_IDX;
-        if (cl == int.class)     return INT_IDX;
+        if (cl == int.class)                             return INT_IDX;
-        if (cl == boolean.class) return BOOLEAN_IDX;
+        if (cl == boolean.class)                         return BOOLEAN_IDX;
-        if (cl == char.class)    return CHAR_IDX;
+        if (cl == char.class)                            return CHAR_IDX;
-        if (cl == long.class)    return LONG_IDX;
+        if (cl == long.class)                            return LONG_IDX;
+        if (FormatConcatItem.class.isAssignableFrom(cl)) return STRING_CONCAT_ITEM;
         throw new IllegalArgumentException("Unexpected class: " + cl);
     }
 
@@ -986,6 +1000,33 @@ public final class StringConcatFactory {
     private static final @Stable MethodHandle[] MIXERS          = new MethodHandle[TYPE_COUNT];
     private static final long INITIAL_CODER = JLA.stringConcatInitialCoder();
 
+    /**
+     * Promote integral types to int.
+     */
+    private static Class<?> promoteToIntType(Class<?> t) {
+        // use int for subword integral types; still need special mixers
+        // and prependers for char, boolean
+        return t == byte.class || t == short.class ? int.class : t;
+    }
+
+    /**
+     * Returns a stringifier for references and floats/doubles only.
+     * Always returns null for other primitives.
+     *
+     * @param t class to stringify
+     * @return stringifier; null, if not available
+     */
+    private static MethodHandle stringifierFor(Class<?> t) {
+        if (t == Object.class) {
+            return objectStringifier();
+        } else if (t == float.class) {
+            return floatStringifier();
+        } else if (t == double.class) {
+            return doubleStringifier();
+        }
+        return null;
+    }
+
     private static MethodHandle stringValueOf(Class<?> ptype) {
         try {
             return MethodHandles.publicLookup()
@@ -998,4 +1039,304 @@ public final class StringConcatFactory {
     private StringConcatFactory() {
         // no instantiation
     }
+
+    /**
+     * Simplified concatenation method to facilitate {@link StringTemplate}
+     * concatenation. This method returns a single concatenation method that
+     * interleaves fragments and values. fragment|value|fragment|value|...|value|fragment.
+     * The number of fragments must be one more that the number of ptypes.
+     * The total number of slots used by the ptypes must be less than or equal
+     * to {@link #MAX_INDY_CONCAT_ARG_SLOTS}.
+     *
+     * @param fragments list of string fragments
+     * @param ptypes    list of expression types
+     *
+     * @return the {@link MethodHandle} for concatenation
+     *
+     * @throws StringConcatException If any of the linkage invariants are violated.
+     * @throws NullPointerException If any of the incoming arguments is null.
+     * @throws IllegalArgumentException If the number of value slots exceed {@link #MAX_INDY_CONCAT_ARG_SLOTS}.
+     *
+     * @since 21
+     */
+    @PreviewFeature(feature=PreviewFeature.Feature.STRING_TEMPLATES)
+    public static MethodHandle makeConcatWithTemplate(
+            List<String> fragments,
+            List<Class<?>> ptypes)
+            throws StringConcatException
+    {
+        Objects.requireNonNull(fragments, "fragments is null");
+        Objects.requireNonNull(ptypes, "ptypes is null");
+        ptypes = List.copyOf(ptypes);
+
+        if (fragments.size() != ptypes.size() + 1) {
+            throw new IllegalArgumentException("fragments size not equal ptypes size plus one");
+        }
+
+        if (ptypes.isEmpty()) {
+            return MethodHandles.constant(String.class, fragments.get(0));
+        }
+
+        Class<?>[] ttypes = new Class<?>[ptypes.size()];
+        MethodHandle[] filters = new MethodHandle[ptypes.size()];
+        int slots = 0;
+
+        int pos = 0;
+        for (Class<?> ptype : ptypes) {
+            slots += ptype == long.class || ptype == double.class ? 2 : 1;
+
+            if (MAX_INDY_CONCAT_ARG_SLOTS < slots) {
+                throw new StringConcatException("Too many concat argument slots: " +
+                        slots + ", can only accept " + MAX_INDY_CONCAT_ARG_SLOTS);
+            }
+
+            boolean isSpecialized = ptype.isPrimitive();
+            boolean isFormatConcatItem = FormatConcatItem.class.isAssignableFrom(ptype);
+            Class<?> ttype = isSpecialized ? promoteToIntType(ptype) :
+                             isFormatConcatItem ? FormatConcatItem.class : Object.class;
+            MethodHandle filter = isFormatConcatItem ? null : stringifierFor(ttype);
+
+            if (filter != null) {
+                filters[pos] = filter;
+                ttype = String.class;
+            }
+
+            ttypes[pos++] = ttype;
+        }
+
+        MethodHandle mh = MethodHandles.dropArguments(newString(), 2, ttypes);
+
+        long initialLengthCoder = INITIAL_CODER;
+        String lastFragment = "";
+        pos = 0;
+        for (String fragment : fragments) {
+            lastFragment = fragment;
+
+            if (ttypes.length <= pos) {
+                break;
+            }
+
+            Class<?> ttype = ttypes[pos];
+            // (long,byte[],ttype) -> long
+            MethodHandle prepender = prepender(lastFragment.isEmpty() ? null : fragment, ttype);
+            initialLengthCoder = JLA.stringConcatMix(initialLengthCoder, fragment);
+            // (byte[],long,ttypes...) -> String (unchanged)
+            mh = MethodHandles.filterArgumentsWithCombiner(mh, 1, prepender,1, 0, 2 + pos);
+
+            pos++;
+        }
+
+        MethodHandle newArrayCombinator = lastFragment.isEmpty() ? newArray() :
+                newArrayWithSuffix(lastFragment);
+        // (long,ttypes...) -> String
+        mh = MethodHandles.foldArgumentsWithCombiner(mh, 0, newArrayCombinator,
+                1 // index
+        );
+
+        pos = 0;
+        for (Class<?> ttype : ttypes) {
+            // (long,ttype) -> long
+            MethodHandle mix = mixer(ttypes[pos]);
+            boolean lastPType = pos == ttypes.length - 1;
+
+            if (lastPType) {
+                // (ttype) -> long
+                mix = MethodHandles.insertArguments(mix, 0, initialLengthCoder);
+                // (ttypes...) -> String
+                mh = MethodHandles.foldArgumentsWithCombiner(mh, 0, mix,
+                        1 + pos // selected argument
+                );
+            } else {
+                // (long,ttypes...) -> String
+                mh = MethodHandles.filterArgumentsWithCombiner(mh, 0, mix,
+                        0, // old-index
+                        1 + pos // selected argument
+                );
+            }
+
+            pos++;
+        }
+
+        mh = MethodHandles.filterArguments(mh, 0, filters);
+        MethodType mt = MethodType.methodType(String.class, ptypes);
+        mh = mh.viewAsType(mt, true);
+
+        return mh;
+    }
+
+    /**
+     * This method breaks up large concatenations into separate
+     * {@link MethodHandle MethodHandles} based on the number of slots required
+     * per {@link MethodHandle}. Each {@link MethodHandle} after the first will
+     * have an extra {@link String} slot for the result from the previous
+     * {@link MethodHandle}.
+     * {@link #makeConcatWithTemplate}
+     * is used to construct the {@link MethodHandle MethodHandles}. The total
+     * number of slots used by the ptypes is open ended. However, care must
+     * be given when combining the {@link MethodHandle MethodHandles} so that
+     * the combine total does not exceed the 255 slot limit.
+     *
+     * @param fragments list of string fragments
+     * @param ptypes    list of expression types
+     * @param maxSlots  maximum number of slots per {@link MethodHandle}.
+     *
+     * @return List of {@link MethodHandle MethodHandles}
+     *
+     * @throws IllegalArgumentException If maxSlots is not between 1 and
+     *                                  MAX_INDY_CONCAT_ARG_SLOTS.
+     * @throws StringConcatException If any of the linkage invariants are violated.
+     * @throws NullPointerException If any of the incoming arguments is null.
+     * @throws IllegalArgumentException If the number of value slots exceed {@link #MAX_INDY_CONCAT_ARG_SLOTS}.
+     *
+     * @since 21
+     */
+    @PreviewFeature(feature=PreviewFeature.Feature.STRING_TEMPLATES)
+    public static List<MethodHandle> makeConcatWithTemplateCluster(
+            List<String> fragments,
+            List<Class<?>> ptypes,
+            int maxSlots)
+            throws StringConcatException
+    {
+        Objects.requireNonNull(fragments, "fragments is null");
+        Objects.requireNonNull(ptypes, "ptypes is null");
+
+        if (fragments.size() != ptypes.size() + 1) {
+            throw new StringConcatException("fragments size not equal ptypes size plus one");
+        }
+
+        if (maxSlots < 1 || MAX_INDY_CONCAT_ARG_SLOTS < maxSlots) {
+            throw new IllegalArgumentException("maxSlots must be between 1 and " +
+                    MAX_INDY_CONCAT_ARG_SLOTS);
+
+        }
+
+        if (ptypes.isEmpty()) {
+            return List.of(MethodHandles.constant(String.class, fragments.get(0)));
+        }
+
+        List<MethodHandle> mhs = new ArrayList<>();
+        List<String> fragmentsSection = new ArrayList<>();
+        List<Class<?>> ptypeSection = new ArrayList<>();
+        int slots = 0;
+
+        int pos = 0;
+        for (Class<?> ptype : ptypes) {
+            boolean lastPType = pos == ptypes.size() - 1;
+            fragmentsSection.add(fragments.get(pos));
+            ptypeSection.add(ptype);
+
+            slots += ptype == long.class || ptype == double.class ? 2 : 1;
+
+            if (maxSlots <= slots || lastPType) {
+                fragmentsSection.add(lastPType ? fragments.get(pos + 1) : "");
+                MethodHandle mh = makeConcatWithTemplate(fragmentsSection,
+                        ptypeSection);
+                mhs.add(mh);
+                fragmentsSection.clear();
+                fragmentsSection.add("");
+                ptypeSection.clear();
+                ptypeSection.add(String.class);
+                slots = 1;
+            }
+
+            pos++;
+        }
+
+        return mhs;
+    }
+
+    /**
+     * This method creates a {@link MethodHandle} expecting one input, the
+     * receiver of the supplied getters. This method uses
+     * {@link #makeConcatWithTemplateCluster}
+     * to create the intermediate {@link MethodHandle MethodHandles}.
+     *
+     * @param fragments list of string fragments
+     * @param getters   list of getter {@link MethodHandle MethodHandles}
+     * @param maxSlots  maximum number of slots per {@link MethodHandle} in
+     *                  cluster.
+     *
+     * @return the {@link MethodHandle} for concatenation
+     *
+     * @throws IllegalArgumentException If maxSlots is not between 1 and
+     *                                  MAX_INDY_CONCAT_ARG_SLOTS or if the
+     *                                  getters don't use the same argument type
+     * @throws StringConcatException If any of the linkage invariants are violated
+     * @throws NullPointerException If any of the incoming arguments is null
+     * @throws IllegalArgumentException If the number of value slots exceed {@link #MAX_INDY_CONCAT_ARG_SLOTS}.
+     *
+     * @since 21
+     */
+    @PreviewFeature(feature=PreviewFeature.Feature.STRING_TEMPLATES)
+    public static MethodHandle makeConcatWithTemplateGetters(
+            List<String> fragments,
+            List<MethodHandle> getters,
+            int maxSlots)
+            throws StringConcatException
+    {
+        Objects.requireNonNull(fragments, "fragments is null");
+        Objects.requireNonNull(getters, "getters is null");
+
+        if (fragments.size() != getters.size() + 1) {
+            throw new StringConcatException("fragments size not equal getters size plus one");
+        }
+
+        if (maxSlots < 1 || MAX_INDY_CONCAT_ARG_SLOTS < maxSlots) {
+            throw new IllegalArgumentException("maxSlots must be between 1 and " +
+                    MAX_INDY_CONCAT_ARG_SLOTS);
+
+        }
+
+        if (getters.size() == 0) {
+            throw new StringConcatException("no getters supplied");
+        }
+
+        Class<?> receiverType = null;
+        List<Class<?>> ptypes = new ArrayList<>();
+
+        for (MethodHandle getter : getters) {
+            MethodType mt = getter.type();
+            Class<?> returnType = mt.returnType();
+
+            if (returnType == void.class || mt.parameterCount() != 1) {
+                throw new StringConcatException("not a getter " + mt);
+            }
+
+            if (receiverType == null) {
+                receiverType = mt.parameterType(0);
+            } else if (receiverType != mt.parameterType(0)) {
+                throw new StringConcatException("not the same receiever type " +
+                        mt + " needs " + receiverType);
+            }
+
+            ptypes.add(returnType);
+        }
+
+        MethodType resultType = MethodType.methodType(String.class, receiverType);
+        List<MethodHandle> clusters = makeConcatWithTemplateCluster(fragments, ptypes,
+                maxSlots);
+
+        MethodHandle mh = null;
+        Iterator<MethodHandle> getterIterator = getters.iterator();
+
+        for (MethodHandle cluster : clusters) {
+            MethodType mt = cluster.type();
+            MethodHandle[] filters = new MethodHandle[mt.parameterCount()];
+            int pos = 0;
+
+            if (mh != null) {
+                filters[pos++] = mh;
+            }
+
+            while (pos < filters.length) {
+                filters[pos++] = getterIterator.next();
+            }
+
+            cluster = MethodHandles.filterArguments(cluster, 0, filters);
+            mh = MethodHandles.permuteArguments(cluster, resultType,
+                    new int[filters.length]);
+        }
+
+        return mh;
+    }
 }

src/java.base/share/classes/java/lang/runtime/ReferenceKey.java

@@ -0,0 +1,230 @@
+/*
+ * Copyright (c) 2023, Oracle and/or its affiliates. All rights reserved.
+ * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
+ *
+ * This code is free software; you can redistribute it and/or modify it
+ * under the terms of the GNU General Public License version 2 only, as
+ * published by the Free Software Foundation.  Oracle designates this
+ * particular file as subject to the "Classpath" exception as provided
+ * by Oracle in the LICENSE file that accompanied this code.
+ *
+ * This code is distributed in the hope that it will be useful, but WITHOUT
+ * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
+ * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
+ * version 2 for more details (a copy is included in the LICENSE file that
+ * accompanied this code).
+ *
+ * You should have received a copy of the GNU General Public License version
+ * 2 along with this work; if not, write to the Free Software Foundation,
+ * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
+ *
+ * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
+ * or visit www.oracle.com if you need additional information or have any
+ * questions.
+ */
+
+package java.lang.runtime;
+
+import java.lang.ref.Reference;
+import java.lang.ref.ReferenceQueue;
+import java.lang.ref.SoftReference;
+import java.lang.ref.WeakReference;
+import java.util.Objects;
+
+/**
+ * View/wrapper of keys used by the backing {@link ReferencedKeyMap}.
+ * There are two style of keys; one for entries in the backing map and
+ * one for queries to the backing map. This second style avoids the
+ * overhead of a {@link Reference} object.
+ *
+ * @param <T> key type
+ *
+ * @since 21
+ *
+ * Warning: This class is part of PreviewFeature.Feature.STRING_TEMPLATES.
+ *          Do not rely on its availability.
+ */
+interface ReferenceKey<T> {
+    /**
+     * {@return the value of the unwrapped key}
+     */
+    T get();
+
+    /**
+     * Cleanup unused key.
+     */
+    void unused();
+
+    /**
+     * {@link WeakReference} wrapper key for entries in the backing map.
+     *
+     * @param <T> key type
+     *
+     * @since 21
+     */
+    class WeakKey<T> extends WeakReference<T> implements ReferenceKey<T> {
+        /**
+         * Saved hashcode of the key. Used when {@link WeakReference} is
+         * null.
+         */
+        private final int hashcode;
+
+        /**
+         * Private constructor.
+         *
+         * @param key   unwrapped key value
+         * @param queue reference queue
+         */
+        WeakKey(T key, ReferenceQueue<T> queue) {
+            super(key, queue);
+            this.hashcode = Objects.hashCode(key);
+        }
+
+        /**
+         * Cleanup unused key. No need to enqueue since the key did not make it
+         * into the map.
+         */
+        @Override
+        public void unused() {
+            clear();
+        }
+
+        @Override
+        public boolean equals(Object obj) {
+            // Necessary when removing a null reference
+            if (obj == this) {
+                return true;
+            }
+            // Necessary when comparing an unwrapped key
+            if (obj instanceof ReferenceKey<?> key) {
+                obj = key.get();
+            }
+            return Objects.equals(get(), obj);
+        }
+
+        @Override
+        public int hashCode() {
+            // Use saved hashcode
+            return hashcode;
+        }
+
+        @Override
+        public String toString() {
+            return this.getClass().getCanonicalName() + "#" + System.identityHashCode(this);
+        }
+    }
+
+    /**
+     * {@link SoftReference} wrapper key for entries in the backing map.
+     *
+     * @param <T> key type
+     *
+     * @since 21
+     */
+    class SoftKey<T> extends SoftReference<T> implements ReferenceKey<T> {
+        /**
+         * Saved hashcode of the key. Used when {@link SoftReference} is
+         * null.
+         */
+        private final int hashcode;
+
+        /**
+         * Private constructor.
+         *
+         * @param key   unwrapped key value
+         * @param queue reference queue
+         */
+        SoftKey(T key, ReferenceQueue<T> queue) {
+            super(key, queue);
+            this.hashcode = Objects.hashCode(key);
+        }
+
+        /**
+         * Cleanup unused key. No need to enqueue since the key did not make it
+         * into the map.
+         */
+        @Override
+        public void unused() {
+            clear();
+        }
+
+        @Override
+        public boolean equals(Object obj) {
+            // Necessary when removing a null reference
+            if (obj == this) {
+                return true;
+            }
+            // Necessary when comparing an unwrapped key
+            if (obj instanceof ReferenceKey<?> key) {
+                obj = key.get();
+            }
+            return Objects.equals(get(), obj);
+        }
+
+        @Override
+        public int hashCode() {
+            // Use saved hashcode
+            return hashcode;
+        }
+
+        @Override
+        public String toString() {
+            return this.getClass().getCanonicalName() + "#" + System.identityHashCode(this);
+        }
+    }
+
+    /**
+     * Wrapper for querying the backing map. Avoids the overhead of an
+     * {@link Reference} object.
+     *
+     * @param <T> key type
+     *
+     * @since 21
+     */
+    class StrongKey<T> implements ReferenceKey<T> {
+        T key;
+
+        /**
+         * Private constructor.
+         *
+         * @param key unwrapped key value
+         */
+        StrongKey(T key) {
+            this.key = key;
+        }
+
+        /**
+         * {@return the unwrapped key}
+         */
+        @Override
+        public T get() {
+            return key;
+        }
+
+        @Override
+        public void unused() {
+            key = null;
+        }
+
+        @Override
+        public boolean equals(Object obj) {
+            // Necessary when comparing an unwrapped key
+            if (obj instanceof ReferenceKey<?> key) {
+                obj = key.get();
+            }
+            return Objects.equals(get(), obj);
+        }
+
+        @Override
+        public int hashCode() {
+            // Use unwrapped key hash code
+            return get().hashCode();
+        }
+
+        @Override
+        public String toString() {
+            return this.getClass().getCanonicalName() + "#" + System.identityHashCode(this);
+        }
+    }
+
+}

src/java.base/share/classes/java/lang/runtime/ReferencedKeyMap.java

@@ -0,0 +1,334 @@
+/*
+ * Copyright (c) 2023, Oracle and/or its affiliates. All rights reserved.
+ * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
+ *
+ * This code is free software; you can redistribute it and/or modify it
+ * under the terms of the GNU General Public License version 2 only, as
+ * published by the Free Software Foundation.  Oracle designates this
+ * particular file as subject to the "Classpath" exception as provided
+ * by Oracle in the LICENSE file that accompanied this code.
+ *
+ * This code is distributed in the hope that it will be useful, but WITHOUT
+ * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
+ * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
+ * version 2 for more details (a copy is included in the LICENSE file that
+ * accompanied this code).
+ *
+ * You should have received a copy of the GNU General Public License version
+ * 2 along with this work; if not, write to the Free Software Foundation,
+ * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
+ *
+ * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
+ * or visit www.oracle.com if you need additional information or have any
+ * questions.
+ */
+
+package java.lang.runtime;
+
+import java.lang.ref.Reference;
+import java.lang.ref.ReferenceQueue;
+import java.lang.ref.SoftReference;
+import java.lang.ref.WeakReference;
+import java.util.AbstractMap;
+import java.util.Collection;
+import java.util.HashMap;
+import java.util.Objects;
+import java.util.Map;
+import java.util.Set;
+import java.util.concurrent.ConcurrentHashMap;
+import java.util.function.Supplier;
+import java.util.stream.Collectors;
+import java.util.stream.Stream;
+
+/**
+ * This class provides management of {@link Map maps} where it is desirable to
+ * remove entries automatically when the key is garbage collected. This is
+ * accomplished by using a backing map where the keys are either a
+ * {@link WeakReference} or a {@link SoftReference}.
+ * <p>
+ * To create a {@link ReferencedKeyMap} the user must provide a {@link Supplier}
+ * of the backing map and whether {@link WeakReference} or
+ * {@link SoftReference} is to be used.
+ *
+ * {@snippet :
+ * // Use HashMap and WeakReference
+ * Map<Long, String> map = ReferencedKeyMap.create(false, HashMap::new);
+ * map.put(10_000_000L, "a");
+ * map.put(10_000_001L, "b");
+ * map.put(10_000_002L, "c");
+ * map.put(10_000_003L, "d");
+ * map.put(10_000_004L, "e");
+ *
+ * // Use ConcurrentHashMap and SoftReference
+ * map = ReferencedKeyMap.create(true, ConcurrentHashMap::new);
+ * map.put(20_000_000L, "v");
+ * map.put(20_000_001L, "w");
+ * map.put(20_000_002L, "x");
+ * map.put(20_000_003L, "y");
+ * map.put(20_000_004L, "z");
+ * }
+ *
+ * @implNote Care must be given that the backing map does replacement by
+ * replacing the value in the map entry instead of deleting the old entry and
+ * adding a new entry, otherwise replaced entries may end up with a strongly
+ * referenced key. {@link HashMap} and {@link ConcurrentHashMap} are known
+ * to be safe.
+ *
+ * @param <K> the type of keys maintained by this map
+ * @param <V> the type of mapped values
+ *
+ * @since 21
+ *
+ * Warning: This class is part of PreviewFeature.Feature.STRING_TEMPLATES.
+ *          Do not rely on its availability.
+ */
+final class ReferencedKeyMap<K, V> implements Map<K, V> {
+    /**
+     * true if {@link SoftReference} keys are to be used,
+     * {@link WeakReference} otherwise.
+     */
+    private final boolean isSoft;
+
+    /**
+     * Backing {@link Map}.
+     */
+    private final Map<ReferenceKey<K>, V> map;
+
+    /**
+     * {@link ReferenceQueue} for cleaning up {@link ReferenceKey.WeakKey EntryKeys}.
+     */
+    private final ReferenceQueue<K> stale;
+
+    /**
+     * Private constructor.
+     *
+     * @param isSoft  true if {@link SoftReference} keys are to
+     *                be used, {@link WeakReference} otherwise.
+     * @param map     backing map
+     */
+    private ReferencedKeyMap(boolean isSoft, Map<ReferenceKey<K>, V> map) {
+        this.isSoft = isSoft;
+        this.map = map;
+        this.stale = new ReferenceQueue<>();
+    }
+
+    /**
+     * Create a new {@link ReferencedKeyMap} map.
+     *
+     * @param isSoft    true if {@link SoftReference} keys are to
+     *                  be used, {@link WeakReference} otherwise.
+     * @param supplier  {@link Supplier} of the backing map
+     *
+     * @return a new map with {@link Reference} keys
+     *
+     * @param <K> the type of keys maintained by the new map
+     * @param <V> the type of mapped values
+     */
+    static <K, V> ReferencedKeyMap<K, V>
+    create(boolean isSoft, Supplier<Map<ReferenceKey<K>, V>> supplier) {
+        return new ReferencedKeyMap<K, V>(isSoft, supplier.get());
+    }
+
+    /**
+     * Create a new {@link ReferencedKeyMap} map using
+     * {@link WeakReference} keys.
+     *
+     * @param supplier  {@link Supplier} of the backing map
+     *
+     * @return a new map with {@link Reference} keys
+     *
+     * @param <K> the type of keys maintained by the new map
+     * @param <V> the type of mapped values
+     */
+    static <K, V> ReferencedKeyMap<K, V>
+    create(Supplier<Map<ReferenceKey<K>, V>> supplier) {
+        return new ReferencedKeyMap<K, V>(false, supplier.get());
+    }
+
+    /**
+     * {@return a key suitable for a map entry}
+     *
+     * @param key unwrapped key
+     */
+    @SuppressWarnings("unchecked")
+    private ReferenceKey<K> entryKey(Object key) {
+        if (isSoft) {
+            return new ReferenceKey.SoftKey<>((K)key, stale);
+        } else {
+            return new ReferenceKey.WeakKey<>((K)key, stale);
+        }
+    }
+
+    /**
+     * {@return a key suitable for lookup}
+     *
+     * @param key unwrapped key
+     */
+    @SuppressWarnings("unchecked")
+    private ReferenceKey<K> lookupKey(Object key) {
+        return new ReferenceKey.StrongKey<>((K)key);
+    }
+
+    @Override
+    public int size() {
+        removeStaleReferences();
+        return map.size();
+    }
+
+    @Override
+    public boolean isEmpty() {
+        removeStaleReferences();
+        return map.isEmpty();
+    }
+
+    @Override
+    public boolean containsKey(Object key) {
+        Objects.requireNonNull(key, "key must not be null");
+        removeStaleReferences();
+        return map.containsKey(lookupKey(key));
+    }
+
+    @Override
+    public boolean containsValue(Object value) {
+        Objects.requireNonNull(value, "value must not be null");
+        removeStaleReferences();
+        return map.containsValue(value);
+    }
+
+    @Override
+    public V get(Object key) {
+        Objects.requireNonNull(key, "key must not be null");
+        removeStaleReferences();
+        return map.get(lookupKey(key));
+    }
+
+    @Override
+    public V put(K key, V newValue) {
+        Objects.requireNonNull(key, "key must not be null");
+        Objects.requireNonNull(newValue, "value must not be null");
+        removeStaleReferences();
+        ReferenceKey<K> entryKey = entryKey(key);
+        // If {@code put} returns non-null then was actually a {@code replace}
+        // and older key was used. In that case the new key was not used and the
+        // reference marked stale.
+        V oldValue = map.put(entryKey, newValue);
+        if (oldValue != null) {
+            entryKey.unused();
+        }
+        return oldValue;
+    }
+
+    @Override
+    public V remove(Object key) {
+        // Rely on gc to clean up old key.
+        return map.remove(lookupKey(key));
+    }
+
+    @Override
+    public void putAll(Map<? extends K, ? extends V> m) {
+        removeStaleReferences();
+        for (Entry<? extends K, ? extends V> entry : m.entrySet()) {
+            K key = entry.getKey();
+            V value = entry.getValue();
+            put(key, value);
+        }
+    }
+
+    @Override
+    public void clear() {
+        removeStaleReferences();
+        // Rely on gc to clean up old keys.
+        map.clear();
+    }
+
+    /**
+     * Common routine for collecting the current set of keys.
+     *
+     * @return {@link Stream} of valid keys (unwrapped)
+     */
+    private Stream<K> filterKeySet() {
+        return map.keySet()
+                .stream()
+                .map(ReferenceKey::get)
+                .filter(Objects::nonNull);
+    }
+
+    @Override
+    public Set<K> keySet() {
+        removeStaleReferences();
+        return filterKeySet().collect(Collectors.toSet());
+    }
+
+    @Override
+    public Collection<V> values() {
+        removeStaleReferences();
+        return map.values();
+    }
+
+    @Override
+    public Set<Entry<K, V>> entrySet() {
+        removeStaleReferences();
+        return filterKeySet()
+                .map(k -> new AbstractMap.SimpleEntry<>(k, get(k)))
+                .collect(Collectors.toSet());
+    }
+
+    @Override
+    public V putIfAbsent(K key, V newValue) {
+        removeStaleReferences();
+        ReferenceKey<K> entryKey = entryKey(key);
+        // If {@code putIfAbsent} returns non-null then was actually a
+        // {@code replace}  and older key was used. In that case the new key was
+        // not used and the reference marked stale.
+        V oldValue = map.putIfAbsent(entryKey, newValue);
+        if (oldValue != null) {
+            entryKey.unused();
+        }
+        return oldValue;
+    }
+
+    @Override
+    public boolean remove(Object key, Object value) {
+        // Rely on gc to clean up old key.
+        return map.remove(lookupKey(key), value);
+    }
+
+    @Override
+    public boolean replace(K key, V oldValue, V newValue) {
+        removeStaleReferences();
+        // If replace is successful then the older key will be used and the
+        // lookup key will suffice.
+        return map.replace(lookupKey(key), oldValue, newValue);
+    }
+
+    @Override
+    public V replace(K key, V value) {
+        removeStaleReferences();
+        // If replace is successful then the older key will be used and the
+        // lookup key will suffice.
+        return map.replace(lookupKey(key), value);
+    }
+
+    @Override
+    public String toString() {
+        removeStaleReferences();
+        return filterKeySet()
+                .map(k -> k + "=" + get(k))
+                .collect(Collectors.joining(", ", "{", "}"));
+    }
+
+    /**
+     * Removes enqueued weak references from map.
+     */
+    @SuppressWarnings("unchecked")
+    public void removeStaleReferences() {
+        while (true) {
+            ReferenceKey.WeakKey<K> key = (ReferenceKey.WeakKey<K>)stale.poll();
+            if (key == null) {
+                break;
+            }
+            map.remove(key);
+        }
+    }
+
+}

src/java.base/share/classes/java/lang/runtime/StringTemplateImpl.java

@@ -0,0 +1,134 @@
+/*
+ * Copyright (c) 2023, Oracle and/or its affiliates. All rights reserved.
+ * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
+ *
+ * This code is free software; you can redistribute it and/or modify it
+ * under the terms of the GNU General Public License version 2 only, as
+ * published by the Free Software Foundation.  Oracle designates this
+ * particular file as subject to the "Classpath" exception as provided
+ * by Oracle in the LICENSE file that accompanied this code.
+ *
+ * This code is distributed in the hope that it will be useful, but WITHOUT
+ * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
+ * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
+ * version 2 for more details (a copy is included in the LICENSE file that
+ * accompanied this code).
+ *
+ * You should have received a copy of the GNU General Public License version
+ * 2 along with this work; if not, write to the Free Software Foundation,
+ * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
+ *
+ * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
+ * or visit www.oracle.com if you need additional information or have any
+ * questions.
+ */
+
+package java.lang.runtime;
+
+import java.lang.invoke.MethodHandle;
+import java.util.List;
+import java.util.Objects;
+
+/**
+ * This class implements specialized {@link StringTemplate StringTemplates} produced by
+ * string template bootstrap method callsites generated by the compiler. Instances of this
+ * class are produced by {@link StringTemplateImplFactory}.
+ * <p>
+ * Values are stored by subclassing {@link Carriers.CarrierObject}. This allows specializations
+ * and sharing of value shapes without creating a new class for each shape.
+ * <p>
+ * {@link StringTemplate} fragments are shared via binding to the
+ * {@link java.lang.invoke.CallSite CallSite's} {@link MethodHandle}.
+ * <p>
+ * The {@link StringTemplateImpl} instance also carries
+ * specialized {@link MethodHandle MethodHandles} for producing the values list and interpolation.
+ * These {@link MethodHandle MethodHandles} are  also shared by binding to the
+ * {@link java.lang.invoke.CallSite CallSite}.
+ *
+ * @since 21
+ *
+ * Warning: This class is part of PreviewFeature.Feature.STRING_TEMPLATES.
+ *          Do not rely on its availability.
+ */
+final class StringTemplateImpl extends Carriers.CarrierObject implements StringTemplate {
+    /**
+     * List of string fragments for the string template. This value of this list is shared by
+     * all instances created at the {@link java.lang.invoke.CallSite CallSite}.
+     */
+    private final List<String> fragments;
+
+    /**
+     * Specialized {@link MethodHandle} used to implement the {@link StringTemplate StringTemplate's}
+     * {@code values} method. This {@link MethodHandle} is shared by all instances created at the
+     * {@link java.lang.invoke.CallSite CallSite}.
+     */
+    private final MethodHandle valuesMH;
+
+    /**
+     * Specialized {@link MethodHandle} used to implement the {@link StringTemplate StringTemplate's}
+     * {@code interpolate} method. This {@link MethodHandle} is shared by all instances created at the
+     * {@link java.lang.invoke.CallSite CallSite}.
+     */
+    private final MethodHandle interpolateMH;
+
+    /**
+     * Constructor.
+     *
+     * @param primitiveCount  number of primitive slots required (bound at callsite)
+     * @param objectCount     number of object slots required (bound at callsite)
+     * @param fragments       list of string fragments (bound in (bound at callsite)
+     * @param valuesMH        {@link MethodHandle} to produce list of values (bound at callsite)
+     * @param interpolateMH   {@link MethodHandle} to produce interpolation (bound at callsite)
+     */
+    StringTemplateImpl(int primitiveCount, int objectCount,
+                       List<String> fragments, MethodHandle valuesMH, MethodHandle interpolateMH) {
+        super(primitiveCount, objectCount);
+        this.fragments = fragments;
+        this.valuesMH = valuesMH;
+        this.interpolateMH = interpolateMH;
+    }
+
+    @Override
+    public List<String> fragments() {
+        return fragments;
+    }
+
+    @Override
+    public List<Object> values() {
+        try {
+            return (List<Object>)valuesMH.invokeExact(this);
+        } catch (RuntimeException | Error ex) {
+            throw ex;
+        } catch (Throwable ex) {
+            throw new RuntimeException("string template values failure", ex);
+        }
+    }
+
+    @Override
+    public String interpolate() {
+        try {
+            return (String)interpolateMH.invokeExact(this);
+        } catch (RuntimeException | Error ex) {
+            throw ex;
+        } catch (Throwable ex) {
+            throw new RuntimeException("string template interpolate failure", ex);
+        }
+    }
+
+    @Override
+    public boolean equals(Object other) {
+        return other instanceof StringTemplate st &&
+                Objects.equals(fragments(), st.fragments()) &&
+                Objects.equals(values(), st.values());
+    }
+
+    @Override
+    public int hashCode() {
+        return Objects.hash(fragments(), values());
+    }
+
+    @Override
+    public String toString() {
+        return StringTemplate.toString(this);
+    }
+}

src/java.base/share/classes/java/lang/runtime/StringTemplateImplFactory.java

@@ -0,0 +1,204 @@
+/*
+ * Copyright (c) 2023, Oracle and/or its affiliates. All rights reserved.
+ * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
+ *
+ * This code is free software; you can redistribute it and/or modify it
+ * under the terms of the GNU General Public License version 2 only, as
+ * published by the Free Software Foundation.  Oracle designates this
+ * particular file as subject to the "Classpath" exception as provided
+ * by Oracle in the LICENSE file that accompanied this code.
+ *
+ * This code is distributed in the hope that it will be useful, but WITHOUT
+ * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
+ * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
+ * version 2 for more details (a copy is included in the LICENSE file that
+ * accompanied this code).
+ *
+ * You should have received a copy of the GNU General Public License version
+ * 2 along with this work; if not, write to the Free Software Foundation,
+ * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
+ *
+ * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
+ * or visit www.oracle.com if you need additional information or have any
+ * questions.
+ */
+
+package java.lang.runtime;
+
+import java.lang.invoke.MethodHandle;
+import java.lang.invoke.MethodHandles;
+import java.lang.invoke.MethodType;
+import java.lang.invoke.StringConcatException;
+import java.lang.invoke.StringConcatFactory;
+import java.util.Arrays;
+import java.util.List;
+
+/**
+ * This class synthesizes {@link StringTemplate StringTemplates} based on
+ * fragments and bootstrap method type. Usage is primarily from
+ * {@link java.lang.runtime.TemplateRuntime}.
+ *
+ * @since 21
+ *
+ * Warning: This class is part of PreviewFeature.Feature.STRING_TEMPLATES.
+ *          Do not rely on its availability.
+ */
+final class StringTemplateImplFactory {
+
+    /**
+     * Private constructor.
+     */
+    StringTemplateImplFactory() {
+        throw new AssertionError("private constructor");
+    }
+
+    /*
+     * {@link StringTemplateImpl} constructor MethodHandle.
+     */
+    private static final MethodHandle CONSTRUCTOR;
+
+
+    /*
+     * Frequently used method types.
+     */
+    private static final MethodType MT_STRING_STIMPL =
+            MethodType.methodType(String.class, StringTemplateImpl.class);
+    private static final MethodType MT_LIST_STIMPL =
+            MethodType.methodType(List.class, StringTemplateImpl.class);
+
+    /**
+     * List (for nullable) of MethodHandle;
+     */
+    private static final MethodHandle TO_LIST;
+
+    static {
+        try {
+            MethodHandles.Lookup lookup = MethodHandles.lookup();
+
+            MethodType mt = MethodType.methodType(void.class, int.class, int.class, List.class,
+                    MethodHandle.class, MethodHandle.class);
+            CONSTRUCTOR = lookup.findConstructor(StringTemplateImpl.class, mt)
+                    .asType(mt.changeReturnType(Carriers.CarrierObject.class));
+
+            mt = MethodType.methodType(List.class, Object[].class);
+            TO_LIST = lookup.findStatic(StringTemplateImplFactory.class, "toList", mt);
+        } catch(ReflectiveOperationException ex) {
+            throw new AssertionError("carrier static init fail", ex);
+        }
+    }
+
+    /**
+     * Create a new {@link StringTemplateImpl} constructor.
+     *
+     * @param fragments  string template fragments
+     * @param type       values types with StringTemplate return
+     *
+     * @return {@link MethodHandle} that can construct a {@link StringTemplateImpl} with arguments
+     * used as values.
+     */
+    static MethodHandle createStringTemplateImplMH(List<String> fragments, MethodType type) {
+        Carriers.CarrierElements elements = Carriers.CarrierFactory.of(type);
+        MethodHandle[] components = elements
+                .components()
+                .stream()
+                .map(c -> c.asType(c.type().changeParameterType(0, StringTemplateImpl.class)))
+                .toArray(MethodHandle[]::new);
+        Class<?>[] ptypes = elements
+                .components()
+                .stream()
+                .map(c -> c.type().returnType())
+                .toArray(Class<?>[]::new);
+        int[] permute = new int[ptypes.length];
+
+        MethodHandle interpolateMH;
+        MethodType mt;
+        try {
+            interpolateMH = StringConcatFactory.makeConcatWithTemplate(fragments, List.of(ptypes));
+        } catch (StringConcatException ex) {
+            throw new RuntimeException("constructing internal string template", ex);
+        }
+        interpolateMH = MethodHandles.filterArguments(interpolateMH, 0, components);
+        interpolateMH = MethodHandles.permuteArguments(interpolateMH, MT_STRING_STIMPL, permute);
+
+        mt = MethodType.methodType(List.class, ptypes);
+        MethodHandle valuesMH = TO_LIST.asCollector(Object[].class, components.length).asType(mt);
+        valuesMH = MethodHandles.filterArguments(valuesMH, 0, components);
+        valuesMH = MethodHandles.permuteArguments(valuesMH, MT_LIST_STIMPL, permute);
+
+        MethodHandle constructor = MethodHandles.insertArguments(CONSTRUCTOR, 0,
+                elements.primitiveCount(), elements.objectCount(),
+                fragments, valuesMH, interpolateMH);
+        constructor = MethodHandles.foldArguments(elements.initializer(), 0, constructor);
+
+        mt = MethodType.methodType(StringTemplate.class, ptypes);
+        constructor = constructor.asType(mt);
+
+        return constructor;
+    }
+
+    /**
+     * Generic {@link StringTemplate}.
+     *
+     * @param fragments  immutable list of string fragments from string template
+     * @param values     immutable list of expression values
+     */
+    private record SimpleStringTemplate(List<String> fragments, List<Object> values)
+            implements StringTemplate {
+        @Override
+        public String toString() {
+            return StringTemplate.toString(this);
+        }
+    }
+
+    /**
+     * Returns a new StringTemplate composed from fragments and values.
+     *
+     * @param fragments array of string fragments
+     * @param values    array of expression values
+     *
+     * @return StringTemplate composed from fragments and values
+     */
+    static StringTemplate newTrustedStringTemplate(String[] fragments, Object[] values) {
+        return new SimpleStringTemplate(List.of(fragments), toList(values));
+    }
+
+    /**
+     * Returns a new StringTemplate composed from fragments and values.
+     *
+     * @param fragments list of string fragments
+     * @param values    array of expression values
+     *
+     * @return StringTemplate composed from fragments and values
+     */
+    static StringTemplate newTrustedStringTemplate(List<String> fragments, Object[] values) {
+        return new SimpleStringTemplate(List.copyOf(fragments), toList(values));
+    }
+
+    /**
+     * Returns a new StringTemplate composed from fragments and values.
+     *
+     * @param fragments list of string fragments
+     * @param values    list of expression values
+     *
+     * @return StringTemplate composed from fragments and values
+     */
+
+    static StringTemplate newStringTemplate(List<String> fragments, List<?> values) {
+        @SuppressWarnings("unchecked")
+        List<Object> copy = (List<Object>)values.stream().toList();
+        return new SimpleStringTemplate(List.copyOf(fragments), copy);
+    }
+
+    /**
+     * Collect nullable elements from an array into a unmodifiable list.
+     * Elements are guaranteed to be safe.
+     *
+     * @param elements  elements to place in list
+     *
+     * @return unmodifiable list.
+     */
+    private static List<Object> toList(Object[] elements) {
+        return Arrays.stream(elements).toList();
+    }
+
+}

src/java.base/share/classes/java/lang/runtime/TemplateRuntime.java

@@ -0,0 +1,269 @@
+/*
+ * Copyright (c) 2023, Oracle and/or its affiliates. All rights reserved.
+ * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
+ *
+ * This code is free software; you can redistribute it and/or modify it
+ * under the terms of the GNU General Public License version 2 only, as
+ * published by the Free Software Foundation.  Oracle designates this
+ * particular file as subject to the "Classpath" exception as provided
+ * by Oracle in the LICENSE file that accompanied this code.
+ *
+ * This code is distributed in the hope that it will be useful, but WITHOUT
+ * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
+ * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
+ * version 2 for more details (a copy is included in the LICENSE file that
+ * accompanied this code).
+ *
+ * You should have received a copy of the GNU General Public License version
+ * 2 along with this work; if not, write to the Free Software Foundation,
+ * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
+ *
+ * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
+ * or visit www.oracle.com if you need additional information or have any
+ * questions.
+ */
+
+package java.lang.runtime;
+
+import java.lang.invoke.CallSite;
+import java.lang.invoke.ConstantCallSite;
+import java.lang.invoke.MethodHandle;
+import java.lang.invoke.MethodHandles;
+import java.lang.invoke.MethodType;
+import java.lang.StringTemplate.Processor;
+import java.lang.StringTemplate.Processor.Linkage;
+import java.util.ArrayList;
+import java.util.Arrays;
+import java.util.Collections;
+import java.util.List;
+import java.util.Objects;
+
+import jdk.internal.access.JavaTemplateAccess;
+import jdk.internal.access.SharedSecrets;
+import jdk.internal.javac.PreviewFeature;
+
+/**
+ * Manages string template bootstrap methods. These methods may be used, for example,
+ * by Java compiler implementations to create {@link StringTemplate} instances. For example,
+ * the java compiler will translate the following code;
+ * {@snippet :
+ * int x = 10;
+ * int y = 20;
+ * StringTemplate st = RAW."\{x} + \{y} = \{x + y}";
+ * }
+ * to byte code that invokes the {@link java.lang.runtime.TemplateRuntime#newStringTemplate}
+ * bootstrap method to construct a {@link CallSite} that accepts two integers and produces a new
+ * {@link StringTemplate} instance.
+ * {@snippet :
+ * MethodHandles.Lookup lookup = MethodHandles.lookup();
+ * MethodType mt = MethodType.methodType(StringTemplate.class, int.class, int.class);
+ * CallSite cs = TemplateRuntime.newStringTemplate(lookup, "", mt, "", " + ", " = ", "");
+ * ...
+ * int x = 10;
+ * int y = 20;
+ * StringTemplate st = (StringTemplate)cs.getTarget().invokeExact(x, y);
+ * }
+ * If the string template requires more than
+ * {@link java.lang.invoke.StringConcatFactory#MAX_INDY_CONCAT_ARG_SLOTS} value slots,
+ * then the java compiler will use the
+ * {@link java.lang.runtime.TemplateRuntime#newLargeStringTemplate} bootstrap method
+ * instead. For example, the java compiler will translate the following code;
+ * {@snippet :
+ * int[] a = new int[1000], b = new int[1000];
+ * ...
+ * StringTemplate st = """
+ *      \{a[0]} - \{b[0]}
+ *      \{a[1]} - \{b[1]}
+ *      ...
+ *      \{a[999]} - \{b[999]}
+ *      """;
+ * }
+ * to byte code that invokes the {@link java.lang.runtime.TemplateRuntime#newLargeStringTemplate}
+ * bootstrap method to construct a {@link CallSite} that accepts an array of integers and produces a new
+ * {@link StringTemplate} instance.
+ * {@snippet :
+ * MethodType mt = MethodType.methodType(StringTemplate.class, String[].class, Object[].class);
+ * CallSite cs = TemplateRuntime.newStringTemplate(lookup, "", mt);
+ * ...
+ * int[] a = new int[1000], b = new int[1000];
+ * ...
+ * StringTemplate st = (StringTemplate)cs.getTarget().invokeExact(
+ *         new String[] { "", " - ", "\n", " - ", "\n", ... " - ", "\n" },
+ *         new Object[] { a[0], b[0], a[1], b[1], ..., a[999], b[999]}
+ *         );
+ * }
+ *
+ * @since 21
+ */
+@PreviewFeature(feature=PreviewFeature.Feature.STRING_TEMPLATES)
+public final class TemplateRuntime {
+    private static final JavaTemplateAccess JTA = SharedSecrets.getJavaTemplateAccess();
+
+    /**
+     * {@link MethodHandle} to {@link TemplateRuntime#defaultProcess}.
+     */
+    private static final MethodHandle DEFAULT_PROCESS_MH;
+
+    /**
+     * {@link MethodHandle} to {@link TemplateRuntime#newTrustedStringTemplate}.
+     */
+    private static final MethodHandle NEW_TRUSTED_STRING_TEMPLATE;
+
+    /**
+     * Initialize {@link MethodHandle MethodHandles}.
+     */
+    static {
+        try {
+            MethodHandles.Lookup lookup = MethodHandles.lookup();
+
+            MethodType mt = MethodType.methodType(Object.class,
+                    List.class, Processor.class, Object[].class);
+            DEFAULT_PROCESS_MH =
+                lookup.findStatic(TemplateRuntime.class, "defaultProcess", mt);
+
+            mt = MethodType.methodType(StringTemplate.class, String[].class, Object[].class);
+            NEW_TRUSTED_STRING_TEMPLATE =
+                lookup.findStatic(StringTemplateImplFactory.class, "newTrustedStringTemplate", mt);
+        } catch (ReflectiveOperationException ex) {
+            throw new AssertionError("string bootstrap fail", ex);
+        }
+    }
+
+    /**
+     * Private constructor.
+     */
+    private TemplateRuntime() {
+        throw new AssertionError("private constructor");
+    }
+
+    /**
+     * String template bootstrap method for creating string templates.
+     * The static arguments include the fragments list.
+     * The non-static arguments are the values.
+     *
+     * @param lookup          method lookup from call site
+     * @param name            method name - not used
+     * @param type            method type
+     *                        (ptypes...) -> StringTemplate
+     * @param fragments       fragment array for string template
+     *
+     * @return {@link CallSite} to handle create string template
+     *
+     * @throws NullPointerException if any of the arguments is null
+     * @throws Throwable            if linkage fails
+     */
+    public static CallSite newStringTemplate(MethodHandles.Lookup lookup,
+                                             String name,
+                                             MethodType type,
+                                             String... fragments) throws Throwable {
+        Objects.requireNonNull(lookup, "lookup is null");
+        Objects.requireNonNull(name, "name is null");
+        Objects.requireNonNull(type, "type is null");
+        Objects.requireNonNull(fragments, "fragments is null");
+
+        MethodHandle mh = StringTemplateImplFactory
+                .createStringTemplateImplMH(List.of(fragments), type).asType(type);
+
+        return new ConstantCallSite(mh);
+    }
+
+    /**
+     * String template bootstrap method for creating large string templates,
+     * i.e., when the number of value slots exceeds
+     * {@link java.lang.invoke.StringConcatFactory#MAX_INDY_CONCAT_ARG_SLOTS}.
+     * The non-static arguments are the fragments array and values array.
+     *
+     * @param lookup          method lookup from call site
+     * @param name            method name - not used
+     * @param type            method type
+     *                        (String[], Object[]) -> StringTemplate
+     *
+     * @return {@link CallSite} to handle create large string template
+     *
+     * @throws NullPointerException if any of the arguments is null
+     * @throws Throwable            if linkage fails
+     */
+    public static CallSite newLargeStringTemplate(MethodHandles.Lookup lookup,
+                                                  String name,
+                                                  MethodType type) throws Throwable {
+        Objects.requireNonNull(lookup, "lookup is null");
+        Objects.requireNonNull(name, "name is null");
+        Objects.requireNonNull(type, "type is null");
+
+        return new ConstantCallSite(NEW_TRUSTED_STRING_TEMPLATE.asType(type));
+    }
+
+    /**
+     * String template bootstrap method for static final processors.
+     * The static arguments include the fragments array  and a {@link MethodHandle}
+     * to retrieve the value of the static final processor.
+     * The non-static arguments are the values.
+     *
+     * @param lookup          method lookup from call site
+     * @param name            method name - not used
+     * @param type            method type
+     *                        (ptypes...) -> Object
+     * @param processorGetter {@link MethodHandle} to get static final processor
+     * @param fragments       fragments from string template
+     *
+     * @return {@link CallSite} to handle string template processing
+     *
+     * @throws NullPointerException if any of the arguments is null
+     * @throws Throwable            if linkage fails
+     *
+     * @implNote this method is likely to be revamped before exiting preview.
+     */
+    public static CallSite processStringTemplate(MethodHandles.Lookup lookup,
+                                                 String name,
+                                                 MethodType type,
+                                                 MethodHandle processorGetter,
+                                                 String... fragments) throws Throwable {
+        Objects.requireNonNull(lookup, "lookup is null");
+        Objects.requireNonNull(name, "name is null");
+        Objects.requireNonNull(type, "type is null");
+        Objects.requireNonNull(processorGetter, "processorGetter is null");
+        Objects.requireNonNull(fragments, "fragments is null");
+
+        Processor<?, ?> processor = (Processor<?, ?>)processorGetter.invoke();
+        MethodHandle mh = processor instanceof Linkage linkage
+                ? linkage.linkage(List.of(fragments), type)
+                : defaultProcessMethodHandle(type, processor, List.of(fragments));
+
+        return new ConstantCallSite(mh);
+    }
+
+    /**
+     * Creates a simple {@link StringTemplate} and then invokes the processor's process method.
+     *
+     * @param fragments fragments from string template
+     * @param processor {@link Processor} to process
+     * @param values    array of expression values
+     *
+     * @return result of processing the string template
+     *
+     * @throws Throwable when {@link Processor#process(StringTemplate)} throws
+     */
+    private static Object defaultProcess(
+            List<String> fragments,
+            Processor<?, ?> processor,
+            Object[] values
+    ) throws Throwable {
+        return processor.process(StringTemplate.of(fragments, Arrays.stream(values).toList()));
+    }
+
+    /**
+     * Generate a {@link MethodHandle} which is effectively invokes
+     * {@code processor.process(new StringTemplate(fragments, values...)}.
+     *
+     * @return default process {@link MethodHandle}
+     */
+    private static MethodHandle defaultProcessMethodHandle(
+            MethodType type,
+            Processor<?, ?> processor,
+            List<String> fragments
+    ) {
+        MethodHandle mh = MethodHandles.insertArguments(DEFAULT_PROCESS_MH, 0, fragments, processor);
+        return mh.asCollector(Object[].class, type.parameterCount()).asType(type);
+    }
+}
+

src/java.base/share/classes/java/lang/runtime/TemplateSupport.java

@@ -0,0 +1,152 @@
+/*
+ * Copyright (c) 2023, Oracle and/or its affiliates. All rights reserved.
+ * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
+ *
+ * This code is free software; you can redistribute it and/or modify it
+ * under the terms of the GNU General Public License version 2 only, as
+ * published by the Free Software Foundation.  Oracle designates this
+ * particular file as subject to the "Classpath" exception as provided
+ * by Oracle in the LICENSE file that accompanied this code.
+ *
+ * This code is distributed in the hope that it will be useful, but WITHOUT
+ * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
+ * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
+ * version 2 for more details (a copy is included in the LICENSE file that
+ * accompanied this code).
+ *
+ * You should have received a copy of the GNU General Public License version
+ * 2 along with this work; if not, write to the Free Software Foundation,
+ * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
+ *
+ * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
+ * or visit www.oracle.com if you need additional information or have any
+ * questions.
+ */
+
+package java.lang.runtime;
+
+import java.util.Iterator;
+import java.util.List;
+import java.util.Objects;
+
+import jdk.internal.access.JavaLangAccess;
+import jdk.internal.access.JavaTemplateAccess;
+import jdk.internal.access.SharedSecrets;
+
+/**
+ * This class provides runtime support for string templates. The methods within
+ * are intended for internal use only.
+ *
+ * @since 21
+ *
+ * Warning: This class is part of PreviewFeature.Feature.STRING_TEMPLATES.
+ *          Do not rely on its availability.
+ */
+final class TemplateSupport implements JavaTemplateAccess {
+
+    /**
+     * Private constructor.
+     */
+    private TemplateSupport() {
+    }
+
+    static {
+        SharedSecrets.setJavaTemplateAccess(new TemplateSupport());
+    }
+
+    private static final JavaLangAccess JLA = SharedSecrets.getJavaLangAccess();
+
+    /**
+     * Returns a StringTemplate composed from fragments and values.
+     *
+     * @implSpec The {@code fragments} list size must be one more that the
+     * {@code values} list size.
+     *
+     * @param fragments list of string fragments
+     * @param values    list of expression values
+     *
+     * @return StringTemplate composed from fragments and values
+     *
+     * @throws IllegalArgumentException if fragments list size is not one more
+     *         than values list size
+     * @throws NullPointerException if fragments is null or values is null or if any fragment is null.
+     *
+     * @implNote Contents of both lists are copied to construct immutable lists.
+     */
+    @Override
+    public StringTemplate of(List<String> fragments, List<?> values) {
+        return StringTemplateImplFactory.newStringTemplate(fragments, values);
+    }
+
+    /**
+     * Creates a string that interleaves the elements of values between the
+     * elements of fragments.
+     *
+     * @param fragments  list of String fragments
+     * @param values     list of expression values
+     *
+     * @return String interpolation of fragments and values
+     */
+    @Override
+    public String interpolate(List<String> fragments, List<?> values) {
+        int fragmentsSize = fragments.size();
+        int valuesSize = values.size();
+        if (fragmentsSize == 1) {
+            return fragments.get(0);
+        }
+        int size = fragmentsSize + valuesSize;
+        String[] strings = new String[size];
+        int i = 0, j = 0;
+        for (; j < valuesSize; j++) {
+            strings[i++] = fragments.get(j);
+            strings[i++] = String.valueOf(values.get(j));
+        }
+        strings[i] = fragments.get(j);
+        return JLA.join("", "", "", strings, size);
+    }
+
+    /**
+     * Combine one or more {@link StringTemplate StringTemplates} to produce a combined {@link StringTemplate}.
+     * {@snippet :
+     * StringTemplate st = StringTemplate.combine("\{a}", "\{b}", "\{c}");
+     * assert st.interpolate().equals("\{a}\{b}\{c}");
+     * }
+     *
+     * @param sts  zero or more {@link StringTemplate}
+     *
+     * @return combined {@link StringTemplate}
+     *
+     * @throws NullPointerException if sts is null or if any element of sts is null
+     */
+    @Override
+    public StringTemplate combine(StringTemplate... sts) {
+        Objects.requireNonNull(sts, "sts must not be null");
+        if (sts.length == 0) {
+            return StringTemplate.of("");
+        } else if (sts.length == 1) {
+            return Objects.requireNonNull(sts[0], "string templates should not be null");
+        }
+        int size = 0;
+        for (StringTemplate st : sts) {
+            Objects.requireNonNull(st, "string templates should not be null");
+            size += st.values().size();
+        }
+        String[] combinedFragments = new String[size + 1];
+        Object[] combinedValues = new Object[size];
+        combinedFragments[0] = "";
+        int fragmentIndex = 1;
+        int valueIndex = 0;
+        for (StringTemplate st : sts) {
+            Iterator<String> iterator = st.fragments().iterator();
+            combinedFragments[fragmentIndex - 1] += iterator.next();
+            while (iterator.hasNext()) {
+                combinedFragments[fragmentIndex++] = iterator.next();
+            }
+            for (Object value : st.values()) {
+                combinedValues[valueIndex++] = value;
+            }
+        }
+        return StringTemplateImplFactory.newTrustedStringTemplate(combinedFragments, combinedValues);
+    }
+
+}

src/java.base/share/classes/java/util/Digits.java

@@ -0,0 +1,283 @@
+/*
+ * Copyright (c) 2023, Oracle and/or its affiliates. All rights reserved.
+ * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
+ *
+ * This code is free software; you can redistribute it and/or modify it
+ * under the terms of the GNU General Public License version 2 only, as
+ * published by the Free Software Foundation.  Oracle designates this
+ * particular file as subject to the "Classpath" exception as provided
+ * by Oracle in the LICENSE file that accompanied this code.
+ *
+ * This code is distributed in the hope that it will be useful, but WITHOUT
+ * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
+ * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
+ * version 2 for more details (a copy is included in the LICENSE file that
+ * accompanied this code).
+ *
+ * You should have received a copy of the GNU General Public License version
+ * 2 along with this work; if not, write to the Free Software Foundation,
+ * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
+ *
+ * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
+ * or visit www.oracle.com if you need additional information or have any
+ * questions.
+ */
+
+package java.util;
+
+import java.lang.invoke.MethodHandle;
+
+import jdk.internal.vm.annotation.Stable;
+
+/**
+ * Digits provides a fast methodology for converting integers and longs to
+ * ASCII strings.
+ *
+ * @since 21
+ */
+sealed interface Digits permits Digits.DecimalDigits, Digits.HexDigits, Digits.OctalDigits {
+    /**
+     * Insert digits for long value in buffer from high index to low index.
+     *
+     * @param value      value to convert
+     * @param buffer     byte buffer to copy into
+     * @param index      insert point + 1
+     * @param putCharMH  method to put character
+     *
+     * @return the last index used
+     *
+     * @throws Throwable if putCharMH fails (unusual).
+     */
+    int digits(long value, byte[] buffer, int index,
+               MethodHandle putCharMH) throws Throwable;
+
+    /**
+     * Calculate the number of digits required to represent the long.
+     *
+     * @param value value to convert
+     *
+     * @return number of digits
+     */
+    int size(long value);
+
+    /**
+     * Digits class for decimal digits.
+     */
+    final class DecimalDigits implements Digits {
+        @Stable
+        private static final short[] DIGITS;
+
+        /**
+         * Singleton instance of DecimalDigits.
+         */
+        static final Digits INSTANCE = new DecimalDigits();
+
+        static {
+            short[] digits = new short[10 * 10];
+
+            for (int i = 0; i < 10; i++) {
+                short hi = (short) ((i + '0') << 8);
+
+                for (int j = 0; j < 10; j++) {
+                    short lo = (short) (j + '0');
+                    digits[i * 10 + j] = (short) (hi | lo);
+                }
+            }
+
+            DIGITS = digits;
+        }
+
+        /**
+         * Constructor.
+         */
+        private DecimalDigits() {
+        }
+
+        @Override
+        public int digits(long value, byte[] buffer, int index,
+                          MethodHandle putCharMH) throws Throwable {
+            boolean negative = value < 0;
+            if (!negative) {
+                value = -value;
+            }
+
+            long q;
+            int r;
+            while (value <= Integer.MIN_VALUE) {
+                q = value / 100;
+                r = (int)((q * 100) - value);
+                value = q;
+                int digits = DIGITS[r];
+
+                putCharMH.invokeExact(buffer, --index, digits & 0xFF);
+                putCharMH.invokeExact(buffer, --index, digits >> 8);
+            }
+
+            int iq, ivalue = (int)value;
+            while (ivalue <= -100) {
+                iq = ivalue / 100;
+                r = (iq * 100) - ivalue;
+                ivalue = iq;
+                int digits = DIGITS[r];
+                putCharMH.invokeExact(buffer, --index, digits & 0xFF);
+                putCharMH.invokeExact(buffer, --index, digits >> 8);
+            }
+
+            if (ivalue < 0) {
+                ivalue = -ivalue;
+            }
+
+            int digits = DIGITS[ivalue];
+            putCharMH.invokeExact(buffer, --index, digits & 0xFF);
+
+            if (9 < ivalue) {
+                putCharMH.invokeExact(buffer, --index, digits >> 8);
+            }
+
+            if (negative) {
+                putCharMH.invokeExact(buffer, --index, (int)'-');
+            }
+
+            return index;
+        }
+
+        @Override
+        public int size(long value) {
+            boolean negative = value < 0;
+            int sign = negative ? 1 : 0;
+
+            if (!negative) {
+                value = -value;
+            }
+
+            long precision = -10;
+            for (int i = 1; i < 19; i++) {
+                if (value > precision)
+                    return i + sign;
+
+                precision = 10 * precision;
+            }
+
+            return 19 + sign;
+        }
+    }
+
+    /**
+     * Digits class for hexadecimal digits.
+     */
+    final class HexDigits implements Digits {
+        @Stable
+        private static final short[] DIGITS;
+
+        /**
+         * Singleton instance of HexDigits.
+         */
+        static final Digits INSTANCE = new HexDigits();
+
+        static {
+            short[] digits = new short[16 * 16];
+
+            for (int i = 0; i < 16; i++) {
+                short hi = (short) ((i < 10 ? i + '0' : i - 10 + 'a') << 8);
+
+                for (int j = 0; j < 16; j++) {
+                    short lo = (short) (j < 10 ? j + '0' : j - 10 + 'a');
+                    digits[(i << 4) + j] = (short) (hi | lo);
+                }
+            }
+
+            DIGITS = digits;
+        }
+
+        /**
+         * Constructor.
+         */
+        private HexDigits() {
+        }
+
+        @Override
+        public int digits(long value, byte[] buffer, int index,
+                          MethodHandle putCharMH) throws Throwable {
+            while ((value & ~0xFF) != 0) {
+                int digits = DIGITS[(int) (value & 0xFF)];
+                value >>>= 8;
+                putCharMH.invokeExact(buffer, --index, digits & 0xFF);
+                putCharMH.invokeExact(buffer, --index, digits >> 8);
+            }
+
+            int digits = DIGITS[(int) (value & 0xFF)];
+            putCharMH.invokeExact(buffer, --index, digits & 0xFF);
+
+            if (0xF < value) {
+                putCharMH.invokeExact(buffer, --index, digits >> 8);
+            }
+
+            return index;
+        }
+
+        @Override
+        public int size(long value) {
+            return value == 0 ? 1 :
+                    67 - Long.numberOfLeadingZeros(value) >> 2;
+        }
+    }
+
+    /**
+     * Digits class for octal digits.
+     */
+    final class OctalDigits implements Digits {
+        @Stable
+        private static final short[] DIGITS;
+
+        /**
+         * Singleton instance of OctalDigits.
+         */
+        static final Digits INSTANCE = new OctalDigits();
+
+        static {
+            short[] digits = new short[8 * 8];
+
+            for (int i = 0; i < 8; i++) {
+                short hi = (short) ((i + '0') << 8);
+
+                for (int j = 0; j < 8; j++) {
+                    short lo = (short) (j + '0');
+                    digits[(i << 3) + j] = (short) (hi | lo);
+                }
+            }
+
+            DIGITS = digits;
+        }
+
+        /**
+         * Constructor.
+         */
+        private OctalDigits() {
+        }
+
+        @Override
+        public int digits(long value, byte[] buffer, int index,
+                          MethodHandle putCharMH) throws Throwable {
+            while ((value & ~0x3F) != 0) {
+                int digits = DIGITS[(int) (value & 0x3F)];
+                value >>>= 6;
+                putCharMH.invokeExact(buffer, --index, digits & 0xFF);
+                putCharMH.invokeExact(buffer, --index, digits >> 8);
+            }
+
+            int digits = DIGITS[(int) (value & 0x3F)];
+            putCharMH.invokeExact(buffer, --index, digits & 0xFF);
+
+            if (7 < value) {
+                putCharMH.invokeExact(buffer, --index, digits >> 8);
+            }
+
+            return index;
+        }
+
+        @Override
+        public int size(long value) {
+            return (66 - Long.numberOfLeadingZeros(value)) / 3;
+        }
+    }
+}

src/java.base/share/classes/java/util/FormatItem.java

@@ -0,0 +1,539 @@
+/*
+ * Copyright (c) 2023, Oracle and/or its affiliates. All rights reserved.
+ * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
+ *
+ * This code is free software; you can redistribute it and/or modify it
+ * under the terms of the GNU General Public License version 2 only, as
+ * published by the Free Software Foundation.  Oracle designates this
+ * particular file as subject to the "Classpath" exception as provided
+ * by Oracle in the LICENSE file that accompanied this code.
+ *
+ * This code is distributed in the hope that it will be useful, but WITHOUT
+ * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
+ * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
+ * version 2 for more details (a copy is included in the LICENSE file that
+ * accompanied this code).
+ *
+ * You should have received a copy of the GNU General Public License version
+ * 2 along with this work; if not, write to the Free Software Foundation,
+ * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
+ *
+ * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
+ * or visit www.oracle.com if you need additional information or have any
+ * questions.
+ */
+
+package java.util;
+
+import java.io.IOException;
+import java.lang.invoke.*;
+import java.lang.invoke.MethodHandles.Lookup;
+import java.nio.ByteOrder;
+import java.nio.charset.StandardCharsets;
+import java.text.DecimalFormatSymbols;
+import java.util.Digits.*;
+import java.util.Formatter.FormatSpecifier;
+
+import jdk.internal.access.JavaLangAccess;
+import jdk.internal.access.SharedSecrets;
+import jdk.internal.util.FormatConcatItem;
+
+import static java.lang.invoke.MethodType.methodType;
+
+/**
+ * A specialized objects used by FormatterBuilder that knows how to insert
+ * themselves into a concatenation performed by StringConcatFactory.
+ *
+ * @since 21
+ *
+ * Warning: This class is part of PreviewFeature.Feature.STRING_TEMPLATES.
+ *          Do not rely on its availability.
+ */
+class FormatItem {
+    private static final JavaLangAccess JLA = SharedSecrets.getJavaLangAccess();
+
+    private static final MethodHandle CHAR_MIX =
+            JLA.stringConcatHelper("mix",
+                    MethodType.methodType(long.class, long.class,char.class));
+
+    private static final MethodHandle STRING_PREPEND =
+            JLA.stringConcatHelper("prepend",
+                    MethodType.methodType(long.class, long.class, byte[].class,
+                            String.class, String.class));
+
+    private static final MethodHandle SELECT_GETCHAR_MH =
+            JLA.stringConcatHelper("selectGetChar",
+                    MethodType.methodType(MethodHandle.class, long.class));
+
+    private static final MethodHandle SELECT_PUTCHAR_MH =
+            JLA.stringConcatHelper("selectPutChar",
+                    MethodType.methodType(MethodHandle.class, long.class));
+
+    private static long charMix(long lengthCoder, char value) {
+        try {
+            return (long)CHAR_MIX.invokeExact(lengthCoder, value);
+        } catch (Error | RuntimeException ex) {
+            throw ex;
+        } catch (Throwable ex) {
+            throw new RuntimeException(ex);
+        }
+    }
+
+    private static long stringMix(long lengthCoder, String value) {
+        return JLA.stringConcatMix(lengthCoder, value);
+    }
+
+    private static long stringPrepend(long lengthCoder, byte[] buffer,
+                                            String value) throws Throwable {
+        return (long)STRING_PREPEND.invokeExact(lengthCoder, buffer, value,
+                (String)null);
+    }
+
+    private static MethodHandle selectGetChar(long indexCoder) throws Throwable {
+        return (MethodHandle)SELECT_GETCHAR_MH.invokeExact(indexCoder);
+    }
+
+    private static MethodHandle selectPutChar(long indexCoder) throws Throwable {
+        return (MethodHandle)SELECT_PUTCHAR_MH.invokeExact(indexCoder);
+    }
+
+    private static final MethodHandle PUT_CHAR_DIGIT;
+
+    static {
+        try {
+            Lookup lookup = MethodHandles.lookup();
+            PUT_CHAR_DIGIT = lookup.findStatic(FormatItem.class, "putByte",
+                    MethodType.methodType(void.class,
+                            byte[].class, int.class, int.class));
+        } catch (ReflectiveOperationException ex) {
+            throw new AssertionError("putByte lookup failed", ex);
+        }
+    }
+
+    private static void putByte(byte[] buffer, int index, int ch) {
+        buffer[index] = (byte)ch;
+    }
+
+    private FormatItem() {
+        throw new AssertionError("private constructor");
+    }
+
+    /**
+     * Decimal value format item.
+     */
+    static final class FormatItemDecimal implements FormatConcatItem {
+        private final char groupingSeparator;
+        private final char zeroDigit;
+        private final char minusSign;
+        private final int digitOffset;
+        private final byte[] digits;
+        private final int length;
+        private final boolean isNegative;
+        private final int width;
+        private final byte prefixSign;
+        private final int groupSize;
+        private final long value;
+        private final boolean parentheses;
+
+        FormatItemDecimal(DecimalFormatSymbols dfs, int width, char sign,
+                          boolean parentheses, int groupSize, long value) throws Throwable {
+            this.groupingSeparator = dfs.getGroupingSeparator();
+            this.zeroDigit = dfs.getZeroDigit();
+            this.minusSign = dfs.getMinusSign();
+            this.digitOffset = this.zeroDigit - '0';
+            int length = DecimalDigits.INSTANCE.size(value);
+            this.digits = new byte[length];
+            DecimalDigits.INSTANCE.digits(value, this.digits, length, PUT_CHAR_DIGIT);
+            this.isNegative = value < 0L;
+            this.length = this.isNegative ? length - 1 : length;
+            this.width = width;
+            this.groupSize = groupSize;
+            this.value = value;
+            this.parentheses = parentheses && isNegative;
+            this.prefixSign = (byte)(isNegative ? (parentheses ? '\0' : minusSign) : sign);
+        }
+
+        private int signLength() {
+            return (prefixSign != '\0' ? 1 : 0) + (parentheses ? 2 : 0);
+        }
+
+        private int groupLength() {
+            return 0 < groupSize ? (length - 1) / groupSize : 0;
+        }
+
+        @Override
+        public long mix(long lengthCoder) {
+            return JLA.stringConcatCoder(zeroDigit) |
+                    (lengthCoder +
+                     Integer.max(length + signLength() + groupLength(), width));
+        }
+
+        @Override
+        public long prepend(long lengthCoder, byte[] buffer) throws Throwable {
+            MethodHandle putCharMH = selectPutChar(lengthCoder);
+
+            if (parentheses) {
+                putCharMH.invokeExact(buffer, (int)--lengthCoder, (int)')');
+            }
+
+            if (0 < groupSize) {
+                int groupIndex = groupSize;
+
+                for (int i = 1; i <= length; i++) {
+                    if (groupIndex-- == 0) {
+                        putCharMH.invokeExact(buffer, (int)--lengthCoder,
+                                (int)groupingSeparator);
+                        groupIndex = groupSize - 1;
+                    }
+
+                    putCharMH.invokeExact(buffer, (int)--lengthCoder,
+                            digits[digits.length - i] + digitOffset);
+                }
+            } else {
+                for (int i = 1; i <= length; i++) {
+                    putCharMH.invokeExact(buffer, (int)--lengthCoder,
+                            digits[digits.length - i] + digitOffset);
+                }
+            }
+
+            for (int i = length + signLength() + groupLength(); i < width; i++) {
+                putCharMH.invokeExact(buffer, (int)--lengthCoder, (int)'0');
+            }
+
+            if (parentheses) {
+                putCharMH.invokeExact(buffer, (int)--lengthCoder, (int)'(');
+            }
+            if (prefixSign != '\0') {
+                putCharMH.invokeExact(buffer, (int)--lengthCoder, (int)prefixSign);
+            }
+
+            return lengthCoder;
+        }
+    }
+
+    /**
+     * Hexadecimal format item.
+     */
+    static final class FormatItemHexadecimal implements FormatConcatItem {
+        private final int width;
+        private final boolean hasPrefix;
+        private final long value;
+        private final int length;
+
+        FormatItemHexadecimal(int width, boolean hasPrefix, long value) {
+            this.width = width;
+            this.hasPrefix = hasPrefix;
+            this.value = value;
+            this.length = HexDigits.INSTANCE.size(value);
+        }
+
+        private int prefixLength() {
+            return hasPrefix ? 2 : 0;
+        }
+
+        private int zeroesLength() {
+            return Integer.max(0, width - length - prefixLength());
+        }
+
+        @Override
+        public long mix(long lengthCoder) {
+            return lengthCoder + length + prefixLength() + zeroesLength();
+        }
+
+        @Override
+        public long prepend(long lengthCoder, byte[] buffer) throws Throwable {
+            MethodHandle putCharMH = selectPutChar(lengthCoder);
+            HexDigits.INSTANCE.digits(value, buffer, (int)lengthCoder, putCharMH);
+            lengthCoder -= length;
+
+            for (int i = 0; i < zeroesLength(); i++) {
+                putCharMH.invokeExact(buffer, (int)--lengthCoder, (int)'0');
+            }
+
+            if (hasPrefix) {
+                putCharMH.invokeExact(buffer, (int)--lengthCoder, (int)'x');
+                putCharMH.invokeExact(buffer, (int)--lengthCoder, (int)'0');
+            }
+
+            return lengthCoder;
+        }
+    }
+
+    /**
+     * Hexadecimal format item.
+     */
+    static final class FormatItemOctal implements FormatConcatItem {
+        private final int width;
+        private final boolean hasPrefix;
+        private final long value;
+        private final int length;
+
+        FormatItemOctal(int width, boolean hasPrefix, long value) {
+            this.width = width;
+            this.hasPrefix = hasPrefix;
+            this.value = value;
+            this.length = OctalDigits.INSTANCE.size(value);
+        }
+
+        private int prefixLength() {
+            return hasPrefix && value != 0 ? 1 : 0;
+        }
+
+        private int zeroesLength() {
+            return Integer.max(0, width - length - prefixLength());
+        }
+
+        @Override
+        public long mix(long lengthCoder) {
+            return lengthCoder + length + prefixLength() + zeroesLength();
+        }
+
+        @Override
+        public long prepend(long lengthCoder, byte[] buffer) throws Throwable {
+            MethodHandle putCharMH = selectPutChar(lengthCoder);
+            OctalDigits.INSTANCE.digits(value, buffer, (int)lengthCoder, putCharMH);
+            lengthCoder -= length;
+
+            for (int i = 0; i < zeroesLength(); i++) {
+                putCharMH.invokeExact(buffer, (int)--lengthCoder, (int)'0');
+            }
+
+            if (hasPrefix && value != 0) {
+                putCharMH.invokeExact(buffer, (int)--lengthCoder, (int)'0');
+            }
+
+            return lengthCoder;
+        }
+    }
+
+    /**
+     * Boolean format item.
+     */
+    static final class FormatItemBoolean implements FormatConcatItem {
+        private final boolean value;
+
+        FormatItemBoolean(boolean value) {
+            this.value = value;
+        }
+
+        @Override
+        public long mix(long lengthCoder) {
+            return lengthCoder + (value ? "true".length() : "false".length());
+        }
+
+        @Override
+        public long prepend(long lengthCoder, byte[] buffer) throws Throwable {
+            MethodHandle putCharMH = selectPutChar(lengthCoder);
+
+            if (value) {
+                putCharMH.invokeExact(buffer, (int)--lengthCoder, (int)'e');
+                putCharMH.invokeExact(buffer, (int)--lengthCoder, (int)'u');
+                putCharMH.invokeExact(buffer, (int)--lengthCoder, (int)'r');
+                putCharMH.invokeExact(buffer, (int)--lengthCoder, (int)'t');
+            } else {
+                putCharMH.invokeExact(buffer, (int)--lengthCoder, (int)'e');
+                putCharMH.invokeExact(buffer, (int)--lengthCoder, (int)'s');
+                putCharMH.invokeExact(buffer, (int)--lengthCoder, (int)'l');
+                putCharMH.invokeExact(buffer, (int)--lengthCoder, (int)'a');
+                putCharMH.invokeExact(buffer, (int)--lengthCoder, (int)'f');
+            }
+
+            return lengthCoder;
+         }
+    }
+
+    /**
+     * Character format item.
+     */
+    static final class FormatItemCharacter implements FormatConcatItem {
+        private final char value;
+
+        FormatItemCharacter(char value) {
+            this.value = value;
+        }
+
+        @Override
+        public long mix(long lengthCoder) {
+            return charMix(lengthCoder, value);
+        }
+
+        @Override
+        public long prepend(long lengthCoder, byte[] buffer) throws Throwable {
+            MethodHandle putCharMH = selectPutChar(lengthCoder);
+            putCharMH.invokeExact(buffer, (int)--lengthCoder, (int)value);
+
+            return lengthCoder;
+        }
+    }
+
+    /**
+     * String format item.
+     */
+    static final class FormatItemString implements FormatConcatItem {
+        private String value;
+
+        FormatItemString(String value) {
+            this.value = value;
+        }
+
+        @Override
+        public long mix(long lengthCoder) {
+            return stringMix(lengthCoder, value);
+        }
+
+        @Override
+        public long prepend(long lengthCoder, byte[] buffer) throws Throwable {
+            return stringPrepend(lengthCoder, buffer, value);
+        }
+    }
+
+    /**
+     * FormatSpecifier format item.
+     */
+    static final class FormatItemFormatSpecifier implements FormatConcatItem {
+        private StringBuilder sb;
+
+        FormatItemFormatSpecifier(FormatSpecifier fs, Locale locale, Object value) {
+            this.sb = new StringBuilder(64);
+            Formatter formatter = new Formatter(this.sb, locale);
+
+            try {
+                fs.print(formatter, value, locale);
+            } catch (IOException ex) {
+                throw new AssertionError("FormatItemFormatSpecifier IOException", ex);
+            }
+        }
+
+        FormatItemFormatSpecifier(Locale locale,
+                                  int flags, int width, int precision,
+                                  Formattable formattable) {
+            this.sb = new StringBuilder(64);
+            Formatter formatter = new Formatter(this.sb, locale);
+            formattable.formatTo(formatter, flags, width, precision);
+        }
+
+        @Override
+        public long mix(long lengthCoder) {
+            return JLA.stringBuilderConcatMix(lengthCoder, sb);
+        }
+
+        @Override
+        public long prepend(long lengthCoder, byte[] buffer) throws Throwable {
+            return JLA.stringBuilderConcatPrepend(lengthCoder, buffer, sb);
+        }
+    }
+
+    protected static abstract sealed class FormatItemModifier implements FormatConcatItem
+        permits FormatItemFillLeft,
+                FormatItemFillRight
+    {
+        private final long itemLengthCoder;
+        protected final FormatConcatItem item;
+
+        FormatItemModifier(FormatConcatItem item) {
+            this.itemLengthCoder = item.mix(0L);
+            this.item = item;
+        }
+
+        int length() {
+            return (int)itemLengthCoder;
+        }
+
+        long coder() {
+            return itemLengthCoder & ~Integer.MAX_VALUE;
+        }
+
+        @Override
+        public abstract long mix(long lengthCoder);
+
+        @Override
+        public abstract long prepend(long lengthCoder, byte[] buffer) throws Throwable;
+    }
+
+    /**
+     * Fill left format item.
+     */
+    static final class FormatItemFillLeft extends FormatItemModifier
+            implements FormatConcatItem {
+        private final int width;
+
+        FormatItemFillLeft(int width, FormatConcatItem item) {
+            super(item);
+            this.width = Integer.max(length(), width);
+        }
+
+        @Override
+        public long mix(long lengthCoder) {
+            return (lengthCoder | coder()) + width;
+        }
+
+        @Override
+        public long prepend(long lengthCoder, byte[] buffer) throws Throwable {
+            MethodHandle putCharMH = selectPutChar(lengthCoder);
+            lengthCoder = item.prepend(lengthCoder, buffer);
+
+            for (int i = length(); i < width; i++) {
+                putCharMH.invokeExact(buffer, (int)--lengthCoder, (int)' ');
+            }
+
+            return lengthCoder;
+        }
+    }
+
+    /**
+     * Fill right format item.
+     */
+    static final class FormatItemFillRight extends FormatItemModifier
+            implements FormatConcatItem {
+        private final int width;
+
+        FormatItemFillRight(int width, FormatConcatItem item) {
+            super(item);
+            this.width = Integer.max(length(), width);
+        }
+
+        @Override
+        public long mix(long lengthCoder) {
+            return (lengthCoder | coder()) + width;
+        }
+
+        @Override
+        public long prepend(long lengthCoder, byte[] buffer) throws Throwable {
+            MethodHandle putCharMH = selectPutChar(lengthCoder);
+
+            for (int i = length(); i < width; i++) {
+                putCharMH.invokeExact(buffer, (int)--lengthCoder, (int)' ');
+            }
+
+            lengthCoder = item.prepend(lengthCoder, buffer);
+
+            return lengthCoder;
+        }
+    }
+
+
+    /**
+     * Null format item.
+     */
+    static final class FormatItemNull implements FormatConcatItem {
+        FormatItemNull() {
+        }
+
+        @Override
+        public long mix(long lengthCoder) {
+            return lengthCoder + "null".length();
+        }
+
+        @Override
+        public long prepend(long lengthCoder, byte[] buffer) throws Throwable {
+            MethodHandle putCharMH = selectPutChar(lengthCoder);
+
+            putCharMH.invokeExact(buffer, (int)--lengthCoder, (int)'l');
+            putCharMH.invokeExact(buffer, (int)--lengthCoder, (int)'l');
+            putCharMH.invokeExact(buffer, (int)--lengthCoder, (int)'u');
+            putCharMH.invokeExact(buffer, (int)--lengthCoder, (int)'n');
+
+            return lengthCoder;
+        }
+    }
+}

src/java.base/share/classes/java/util/FormatProcessor.java

@@ -0,0 +1,286 @@
+/*
+ * Copyright (c) 2023, Oracle and/or its affiliates. All rights reserved.
+ * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
+ *
+ * This code is free software; you can redistribute it and/or modify it
+ * under the terms of the GNU General Public License version 2 only, as
+ * published by the Free Software Foundation.  Oracle designates this
+ * particular file as subject to the "Classpath" exception as provided
+ * by Oracle in the LICENSE file that accompanied this code.
+ *
+ * This code is distributed in the hope that it will be useful, but WITHOUT
+ * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
+ * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
+ * version 2 for more details (a copy is included in the LICENSE file that
+ * accompanied this code).
+ *
+ * You should have received a copy of the GNU General Public License version
+ * 2 along with this work; if not, write to the Free Software Foundation,
+ * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
+ *
+ * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
+ * or visit www.oracle.com if you need additional information or have any
+ * questions.
+ */
+
+package java.util;
+
+import java.lang.invoke.MethodHandle;
+import java.lang.invoke.MethodHandles;
+import java.lang.invoke.MethodType;
+import java.lang.StringTemplate.Processor;
+import java.lang.StringTemplate.Processor.Linkage;
+import java.util.regex.Matcher;
+
+import jdk.internal.javac.PreviewFeature;
+
+/**
+ * This {@link Processor} constructs a {@link String} result using
+ * {@link Formatter} specifications and values found in the {@link StringTemplate}.
+ * Unlike {@link Formatter}, {@link FormatProcessor} uses the value from the
+ * embedded expression that immediately follows, without whitespace, the
+ * <a href="../util/Formatter.html#syntax">format specifier</a>.
+ * For example:
+ * {@snippet :
+ * FormatProcessor fmt = FormatProcessor.create(Locale.ROOT);
+ * int x = 10;
+ * int y = 20;
+ * String result = fmt."%05d\{x} + %05d\{y} = %05d\{x + y}";
+ * }
+ * In the above example, the value of {@code result} will be {@code "00010 + 00020 = 00030"}.
+ * <p>
+ * Embedded expressions without a preceeding format specifier, use {@code %s}
+ * by default.
+ * {@snippet :
+ * FormatProcessor fmt = FormatProcessor.create(Locale.ROOT);
+ * int x = 10;
+ * int y = 20;
+ * String result1 = fmt."\{x} + \{y} = \{x + y}";
+ * String result2 = fmt."%s\{x} + %s\{y} = %s\{x + y}";
+ * }
+ * In the above example, the value of {@code result1} and {@code result2} will
+ * both be {@code "10 + 20 = 30"}.
+ * <p>
+ * The {@link FormatProcessor} format specification used and exceptions thrown are the
+ * same as those of {@link Formatter}.
+ * <p>
+ * However, there are two significant differences related to the position of arguments.
+ * An explict {@code n$} and relative {@code <} index will cause an exception due to
+ * a missing argument list.
+ * Whitespace appearing between the specification and the embedded expression will
+ * also cause an exception.
+ * <p>
+ * {@link FormatProcessor} allows the use of different locales. For example:
+ * {@snippet :
+ * Locale locale = Locale.forLanguageTag("th-TH-u-nu-thai");
+ * FormatProcessor thaiFMT = FormatProcessor.create(locale);
+ * int x = 10;
+ * int y = 20;
+ * String result = thaiFMT."%4d\{x} + %4d\{y} = %5d\{x + y}";
+ * }
+ * In the above example, the value of {@code result} will be
+ * {@code "  \u0E51\u0E50 +   \u0E52\u0E50 =    \u0E53\u0E50"}.
+ * <p>
+ * For day to day use, the predefined {@link FormatProcessor#FMT} {@link FormatProcessor}
+ * is available. {@link FormatProcessor#FMT} is defined using the {@link Locale#ROOT}.
+ * Example: {@snippet :
+ * int x = 10;
+ * int y = 20;
+ * String result = FMT."0x%04x\{x} + 0x%04x\{y} = 0x%04x\{x + y}"; // @highlight substring="FMT"
+ * }
+ * In the above example, the value of {@code result} will be {@code "0x000a + 0x0014 = 0x001E"}.
+ *
+ * @since 21
+ *
+ * @see Processor
+ */
+@PreviewFeature(feature=PreviewFeature.Feature.STRING_TEMPLATES)
+public final class FormatProcessor implements Processor<String, RuntimeException>, Linkage {
+    /**
+     * {@link Locale} used to format
+     */
+    private final Locale locale;
+
+    /**
+     * Constructor.
+     *
+     * @param locale  {@link Locale} used to format
+     */
+    private FormatProcessor(Locale locale) {
+        this.locale = locale;
+    }
+
+    /**
+     * Create a new {@link FormatProcessor} using the specified locale.
+     *
+     * @param locale {@link Locale} used to format
+     *
+     * @return a new instance of {@link FormatProcessor}
+     *
+     * @throws java.lang.NullPointerException if locale is null
+     */
+    public static FormatProcessor create(Locale locale) {
+        Objects.requireNonNull(locale);
+        return new FormatProcessor(locale);
+    }
+
+    /**
+     * Constructs a {@link String} based on the fragments, format
+     * specifications found in the fragments and values in the
+     * supplied {@link StringTemplate} object. This method constructs a
+     * format string from the fragments, gathers up the values and
+     * evaluates the expression asif evaulating
+     * {@code new Formatter(locale).format(format, values).toString()}.
+     * <p>
+     * If an embedded expression is not immediately preceded by a
+     * specifier then a {@code %s} is inserted in the format.
+     *
+     * @param stringTemplate  a {@link StringTemplate} instance
+     *
+     * @return constructed {@link String}
+
+     * @throws  IllegalFormatException
+     *          If a format specifier contains an illegal syntax, a format
+     *          specifier that is incompatible with the given arguments,
+     *          a specifier not followed immediately by an embedded expression or
+     *          other illegal conditions. For specification of all possible
+     *          formatting errors, see the
+     *          <a href="../util/Formatter.html#detail">details</a>
+     *          section of the formatter class specification.
+     * @throws NullPointerException if stringTemplate is null
+     *
+     * @see java.util.Formatter
+     */
+    @Override
+    public final String process(StringTemplate stringTemplate) {
+        Objects.requireNonNull(stringTemplate);
+        String format = stringTemplateFormat(stringTemplate.fragments());
+        Object[] values = stringTemplate.values().toArray();
+
+        return new Formatter(locale).format(format, values).toString();
+    }
+
+    /**
+     * Constructs a {@link MethodHandle} that when supplied with the values from
+     * a {@link StringTemplate} will produce a result equivalent to that provided by
+     * {@link FormatProcessor#process(StringTemplate)}. This {@link MethodHandle}
+     * is used by {@link FormatProcessor#FMT} and the ilk to perform a more
+     * specialized composition of a result. This specialization is done by
+     * prescanning the fragments and value types of a {@link StringTemplate}.
+     * <p>
+     * Process template expressions can be specialized  when the processor is
+     * of type {@link Linkage} and fetched from a static constant as is
+     * {@link FormatProcessor#FMT} ({@code static final FormatProcessor}).
+     * <p>
+     * Other {@link FormatProcessor FormatProcessors} can be specialized when stored in a static
+     * final.
+     * For example:
+     * {@snippet :
+     * FormatProcessor THAI_FMT = FormatProcessor.create(Locale.forLanguageTag("th-TH-u-nu-thai"));
+     * }
+     * {@code THAI_FMT} will now produce specialized {@link MethodHandle MethodHandles} by way
+     * of {@link FormatProcessor#linkage(List, MethodType)}.
+     *
+     * See {@link FormatProcessor#process(StringTemplate)} for more information.
+     *
+     * @throws  IllegalFormatException
+     *          If a format specifier contains an illegal syntax, a format
+     *          specifier that is incompatible with the given arguments,
+     *          a specifier not followed immediately by an embedded expression or
+     *          other illegal conditions. For specification of all possible
+     *          formatting errors, see the
+     *          <a href="../util/Formatter.html#detail">details</a>
+     *          section of the formatter class specification.
+     * @throws NullPointerException if fragments or type is null
+     *
+     * @see java.util.Formatter
+     */
+    @Override
+    public MethodHandle linkage(List<String> fragments, MethodType type) {
+        Objects.requireNonNull(fragments);
+        Objects.requireNonNull(type);
+        String format = stringTemplateFormat(fragments);
+        Class<?>[] ptypes = type.dropParameterTypes(0, 1).parameterArray();
+        MethodHandle mh = new FormatterBuilder(format, locale, ptypes).build();
+        mh = MethodHandles.dropArguments(mh, 0, type.parameterType(0));
+
+        return mh;
+    }
+
+    /**
+     * Find a format specification at the end of a fragment.
+     *
+     * @param fragment  fragment to check
+     * @param needed    if the specification is needed
+     *
+     * @return true if the specification is found and needed
+     *
+     * @throws MissingFormatArgumentException if not at end or found and not needed
+     */
+    private static boolean findFormat(String fragment, boolean needed) {
+        Matcher matcher = Formatter.FORMAT_SPECIFIER_PATTERN.matcher(fragment);
+        String group;
+
+        while (matcher.find()) {
+            group = matcher.group();
+
+            if (!group.equals("%%") && !group.equals("%n")) {
+                if (matcher.end() == fragment.length() && needed) {
+                    return true;
+                }
+
+                throw new MissingFormatArgumentException(group +
+                        " is not immediately followed by an embedded expression");
+            }
+        }
+
+        return false;
+    }
+
+    /**
+     * Convert {@link StringTemplate} fragments, containing format specifications,
+     * to a form that can be passed on to {@link Formatter}. The method scans each fragment,
+     * matching up formatter specifications with the following expression. If no
+     * specification is found, the method inserts "%s".
+     *
+     * @param fragments  string template fragments
+     *
+     * @return  format string
+     */
+    private static String stringTemplateFormat(List<String> fragments) {
+        StringBuilder sb = new StringBuilder();
+        int lastIndex = fragments.size() - 1;
+        List<String> formats = fragments.subList(0, lastIndex);
+        String last = fragments.get(lastIndex);
+
+        for (String format : formats) {
+            if (findFormat(format, true)) {
+                sb.append(format);
+            } else {
+                sb.append(format);
+                sb.append("%s");
+            }
+        }
+
+        if (!findFormat(last, false)) {
+            sb.append(last);
+        }
+
+        return sb.toString();
+    }
+
+    /**
+     * This predefined {@link FormatProcessor} instance constructs a {@link String} result using
+     * the Locale.ROOT {@link Locale}. See {@link FormatProcessor} for more details.
+     * Example: {@snippet :
+     * int x = 10;
+     * int y = 20;
+     * String result = FMT."0x%04x\{x} + 0x%04x\{y} = 0x%04x\{x + y}"; // @highlight substring="FMT"
+     * }
+     * In the above example, the value of {@code result} will be {@code "0x000a + 0x0014 = 0x001E"}.
+     *
+     * @see java.util.FormatProcessor
+     */
+    public static final FormatProcessor FMT = FormatProcessor.create(Locale.ROOT);
+
+}

src/java.base/share/classes/java/util/Formatter.java

@@ -36,6 +36,7 @@ import java.io.OutputStream;
 import java.io.OutputStreamWriter;
 import java.io.PrintStream;
 import java.io.UnsupportedEncodingException;
+import java.lang.invoke.MethodHandle;
 import java.math.BigDecimal;
 import java.math.BigInteger;
 import java.math.MathContext;
@@ -60,6 +61,7 @@ import java.time.temporal.TemporalAccessor;
 import java.time.temporal.TemporalQueries;
 import java.time.temporal.UnsupportedTemporalTypeException;
 
+import jdk.internal.javac.PreviewFeature;
 import jdk.internal.math.DoubleConsts;
 import jdk.internal.math.FormattedFPDecimal;
 import sun.util.locale.provider.LocaleProviderAdapter;
@@ -2770,8 +2772,7 @@ public final class Formatter implements Closeable, Flushable {
         int lasto = -1;
 
         List<FormatString> fsa = parse(format);
-        for (int i = 0; i < fsa.size(); i++) {
+        for (FormatString fs : fsa) {
-            var fs = fsa.get(i);
             int index = fs.index();
             try {
                 switch (index) {
@@ -2789,7 +2790,7 @@ public final class Formatter implements Closeable, Flushable {
                             throw new MissingFormatArgumentException(fs.toString());
                         fs.print(this, (args == null ? null : args[lasto]), l);
                     }
-                    default -> {  // explicit index
+                    default -> { // explicit index
                         last = index - 1;
                         if (args != null && last > args.length - 1)
                             throw new MissingFormatArgumentException(fs.toString());
@@ -2804,15 +2805,15 @@ public final class Formatter implements Closeable, Flushable {
     }
 
     // %[argument_index$][flags][width][.precision][t]conversion
-    private static final String formatSpecifier
+    static final String FORMAT_SPECIFIER
         = "%(\\d+\\$)?([-#+ 0,(\\<]*)?(\\d+)?(\\.\\d+)?([tT])?([a-zA-Z%])";
 
-    private static final Pattern fsPattern = Pattern.compile(formatSpecifier);
+    static final Pattern FORMAT_SPECIFIER_PATTERN = Pattern.compile(FORMAT_SPECIFIER);
 
     /**
      * Finds format specifiers in the format string.
      */
-    private List<FormatString> parse(String s) {
+    static List<FormatString> parse(String s) {
         ArrayList<FormatString> al = new ArrayList<>();
         int i = 0;
         int max = s.length();
@@ -2840,7 +2841,7 @@ public final class Formatter implements Closeable, Flushable {
                 i++;
             } else {
                 if (m == null) {
-                    m = fsPattern.matcher(s);
+                    m = FORMAT_SPECIFIER_PATTERN.matcher(s);
                 }
                 // We have already parsed a '%' at n, so we either have a
                 // match or the specifier at n is invalid
@@ -2855,7 +2856,7 @@ public final class Formatter implements Closeable, Flushable {
         return al;
     }
 
-    private interface FormatString {
+    interface FormatString {
         int index();
         void print(Formatter fmt, Object arg, Locale l) throws IOException;
         String toString();
@@ -2891,14 +2892,15 @@ public final class Formatter implements Closeable, Flushable {
         DECIMAL_FLOAT
     };
 
-    private static class FormatSpecifier implements FormatString {
+    static class FormatSpecifier implements FormatString {
+        private static final double SCALEUP = Math.scalb(1.0, 54);
 
-        private int index = 0;
+        int index = 0;
-        private int flags = Flags.NONE;
+        int flags = Flags.NONE;
-        private int width = -1;
+        int width = -1;
-        private int precision = -1;
+        int precision = -1;
-        private boolean dt = false;
+        boolean dt = false;
-        private char c;
+        char c;
 
         private void index(String s, int start, int end) {
             if (start >= 0) {
@@ -3548,8 +3550,8 @@ public final class Formatter implements Closeable, Flushable {
                 if (width != -1) {
                     newW = adjustWidth(width - exp.length - 1, flags, neg);
                 }
-                localizedMagnitude(fmt, sb, mant, 0, flags, newW, l);
 
+                localizedMagnitude(fmt, sb, mant, 0, flags, newW, l);
                 sb.append(Flags.contains(flags, Flags.UPPERCASE) ? 'E' : 'e');
 
                 char sign = exp[0];
@@ -3719,8 +3721,7 @@ public final class Formatter implements Closeable, Flushable {
                 // If this is subnormal input so normalize (could be faster to
                 // do as integer operation).
                 if (subnormal) {
-                    double scaleUp = Math.scalb(1.0, 54);
+                    d *= SCALEUP;
-                    d *= scaleUp;
                     // Calculate the exponent.  This is not just exponent + 54
                     // since the former is not the normalized exponent.
                     exponent = Math.getExponent(d);
@@ -4623,7 +4624,7 @@ public final class Formatter implements Closeable, Flushable {
         }
     }
 
-    private static class Flags {
+    static class Flags {
 
         static final int NONE          = 0;      // ''
 
@@ -4701,7 +4702,7 @@ public final class Formatter implements Closeable, Flushable {
         }
     }
 
-    private static class Conversion {
+    static class Conversion {
         // Byte, Short, Integer, Long, BigInteger
         // (and associated primitives due to autoboxing)
         static final char DECIMAL_INTEGER     = 'd';
@@ -4826,7 +4827,7 @@ public final class Formatter implements Closeable, Flushable {
         }
     }
 
-    private static class DateTime {
+    static class DateTime {
         static final char HOUR_OF_DAY_0 = 'H'; // (00 - 23)
         static final char HOUR_0        = 'I'; // (01 - 12)
         static final char HOUR_OF_DAY   = 'k'; // (0 - 23) -- like H
@@ -4877,4 +4878,5 @@ public final class Formatter implements Closeable, Flushable {
             };
         }
     }
+
 }

src/java.base/share/classes/java/util/FormatterBuilder.java

@@ -0,0 +1,489 @@
+/*
+ * Copyright (c) 2023, Oracle and/or its affiliates. All rights reserved.
+ * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
+ *
+ * This code is free software; you can redistribute it and/or modify it
+ * under the terms of the GNU General Public License version 2 only, as
+ * published by the Free Software Foundation.  Oracle designates this
+ * particular file as subject to the "Classpath" exception as provided
+ * by Oracle in the LICENSE file that accompanied this code.
+ *
+ * This code is distributed in the hope that it will be useful, but WITHOUT
+ * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
+ * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
+ * version 2 for more details (a copy is included in the LICENSE file that
+ * accompanied this code).
+ *
+ * You should have received a copy of the GNU General Public License version
+ * 2 along with this work; if not, write to the Free Software Foundation,
+ * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
+ *
+ * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
+ * or visit www.oracle.com if you need additional information or have any
+ * questions.
+ */
+
+package java.util;
+
+import java.io.IOException;
+import java.lang.invoke.*;
+import java.lang.invoke.MethodHandles.Lookup;
+import java.text.DecimalFormat;
+import java.text.DecimalFormatSymbols;
+import java.text.NumberFormat;
+import java.text.spi.NumberFormatProvider;
+import java.util.FormatItem.*;
+import java.util.Formatter.*;
+
+import jdk.internal.util.FormatConcatItem;
+
+import sun.invoke.util.Wrapper;
+import sun.util.locale.provider.LocaleProviderAdapter;
+import sun.util.locale.provider.ResourceBundleBasedAdapter;
+
+import static java.util.Formatter.Conversion.*;
+import static java.util.Formatter.Flags.*;
+import static java.lang.invoke.MethodHandles.*;
+import static java.lang.invoke.MethodType.*;
+
+/**
+ * This package private class supports the construction of the {@link MethodHandle}
+ * used by {@link FormatProcessor}.
+ *
+ * @since 21
+ *
+ * Warning: This class is part of PreviewFeature.Feature.STRING_TEMPLATES.
+ *          Do not rely on its availability.
+ */
+final class FormatterBuilder {
+    private static final Lookup LOOKUP = lookup();
+
+    private final String format;
+    private final Locale locale;
+    private final Class<?>[] ptypes;
+    private final DecimalFormatSymbols dfs;
+    private final boolean isGenericDFS;
+
+    FormatterBuilder(String format, Locale locale, Class<?>[] ptypes) {
+        this.format = format;
+        this.locale = locale;
+        this.ptypes = ptypes;
+        this.dfs = DecimalFormatSymbols.getInstance(locale);
+        this.isGenericDFS = isGenericDFS(this.dfs);
+    }
+
+    private static boolean isGenericDFS(DecimalFormatSymbols dfs) {
+        return dfs.getZeroDigit() == '0' &&
+               dfs.getDecimalSeparator() == '.' &&
+               dfs.getGroupingSeparator() == ',' &&
+               dfs.getMinusSign() == '-';
+    }
+
+    private static Class<?> mapType(Class<?> type) {
+        return type.isPrimitive() || type == String.class ? type : Object.class;
+    }
+
+    private static MethodHandle findStringConcatItemConstructor(Class<?> cls,
+                                          Class<?>... ptypes) {
+        MethodType methodType = methodType(void.class, ptypes);
+
+        try {
+            MethodHandle mh = LOOKUP.findConstructor(cls, methodType);
+
+            return mh.asType(mh.type().changeReturnType(FormatConcatItem.class));
+        } catch (ReflectiveOperationException e) {
+            throw new AssertionError("Missing constructor in " +
+                    cls + ": " + methodType);
+        }
+    }
+
+    private static MethodHandle findMethod(Class<?> cls, String name,
+                                           Class<?> rType, Class<?>... ptypes) {
+        MethodType methodType = methodType(rType, ptypes);
+
+        try {
+            return LOOKUP.findVirtual(cls, name, methodType);
+        } catch (ReflectiveOperationException e) {
+            throw new AssertionError("Missing method in " +
+                    cls + ": " + name + " " + methodType);
+        }
+    }
+
+    private static MethodHandle findStaticMethod(Class<?> cls, String name,
+                                                 Class<?> rType, Class<?>... ptypes) {
+        MethodType methodType = methodType(rType, ptypes);
+
+        try {
+            return LOOKUP.findStatic(cls, name, methodType);
+        } catch (ReflectiveOperationException e) {
+            throw new AssertionError("Missing static method in " +
+                    cls + ": " + name + " " + methodType);
+        }
+    }
+
+    private static final MethodHandle FIDecimal_MH =
+            findStringConcatItemConstructor(FormatItemDecimal.class,
+                    DecimalFormatSymbols.class, int.class, char.class, boolean.class,
+                    int.class, long.class);
+
+    private static final MethodHandle FIHexadecimal_MH =
+            findStringConcatItemConstructor(FormatItemHexadecimal.class,
+                    int.class, boolean.class, long.class);
+
+    private static final MethodHandle FIOctal_MH =
+            findStringConcatItemConstructor(FormatItemOctal.class,
+                    int.class, boolean.class, long.class);
+
+    private static final MethodHandle FIBoolean_MH =
+            findStringConcatItemConstructor(FormatItemBoolean.class,
+                    boolean.class);
+
+    private static final MethodHandle FICharacter_MH =
+            findStringConcatItemConstructor(FormatItemCharacter.class,
+                    char.class);
+
+    private static final MethodHandle FIString_MH =
+            findStringConcatItemConstructor(FormatItemString.class,
+                    String.class);
+
+    private static final MethodHandle FIFormatSpecifier_MH =
+            findStringConcatItemConstructor(FormatItemFormatSpecifier.class,
+                    FormatSpecifier.class, Locale.class, Object.class);
+
+    private static final MethodHandle FIFormattable_MH =
+            findStringConcatItemConstructor(FormatItemFormatSpecifier.class,
+                    Locale.class, int.class, int.class, int.class,
+                    Formattable.class);
+
+    private static final MethodHandle FIFillLeft_MH =
+             findStringConcatItemConstructor(FormatItemFillLeft.class,
+                    int.class, FormatConcatItem.class);
+
+    private static final MethodHandle FIFillRight_MH =
+            findStringConcatItemConstructor(FormatItemFillRight.class,
+                     int.class, FormatConcatItem.class);
+
+    private static final MethodHandle FINull_MH =
+            findStringConcatItemConstructor(FormatItemNull.class);
+
+    private static final MethodHandle NullCheck_MH =
+            findStaticMethod(FormatterBuilder.class, "nullCheck", boolean.class,
+                    Object.class);
+
+    private static final MethodHandle FormattableCheck_MH =
+            findStaticMethod(FormatterBuilder.class, "formattableCheck", boolean.class,
+                    Object.class);
+
+    private static final MethodHandle ToLong_MH =
+            findStaticMethod(java.util.FormatterBuilder.class, "toLong", long.class,
+                    int.class);
+
+    private static final MethodHandle ToString_MH =
+            findStaticMethod(String.class, "valueOf", String.class,
+                    Object.class);
+
+    private static final MethodHandle HashCode_MH =
+            findStaticMethod(Objects.class, "hashCode", int.class,
+                    Object.class);
+
+    private static boolean nullCheck(Object object) {
+        return object == null;
+    }
+
+    private static boolean formattableCheck(Object object) {
+        return Formattable.class.isAssignableFrom(object.getClass());
+    }
+
+    private static long toLong(int value) {
+        return (long)value & 0xFFFFFFFFL;
+    }
+
+    private static boolean isFlag(int value, int flags) {
+        return (value & flags) != 0;
+    }
+
+    private static boolean validFlags(int value, int flags) {
+        return (value & ~flags) == 0;
+    }
+
+    private static int groupSize(Locale locale, DecimalFormatSymbols dfs) {
+        if (isGenericDFS(dfs)) {
+            return 3;
+        }
+
+        DecimalFormat df;
+        NumberFormat nf = NumberFormat.getNumberInstance(locale);
+
+        if (nf instanceof DecimalFormat) {
+            df = (DecimalFormat)nf;
+        } else {
+            LocaleProviderAdapter adapter = LocaleProviderAdapter
+                    .getAdapter(NumberFormatProvider.class, locale);
+
+            if (!(adapter instanceof ResourceBundleBasedAdapter)) {
+                adapter = LocaleProviderAdapter.getResourceBundleBased();
+            }
+
+            String[] all = adapter.getLocaleResources(locale)
+                    .getNumberPatterns();
+
+            df = new DecimalFormat(all[0], dfs);
+        }
+
+        return df.isGroupingUsed() ? df.getGroupingSize() : 0;
+    }
+
+    private MethodHandle formatSpecifier(FormatSpecifier fs, Class<?> ptype) {
+        boolean isPrimitive = ptype.isPrimitive();
+        MethodHandle mh = identity(ptype);
+        MethodType mt = mh.type();
+
+//cannot cast to primitive types as it breaks null values formatting
+//        if (ptype == byte.class || ptype == short.class ||
+//            ptype == Byte.class || ptype == Short.class ||
+//            ptype == Integer.class) {
+//            mt = mt.changeReturnType(int.class);
+//        } else if (ptype == Long.class) {
+//            mt = mt.changeReturnType(long.class);
+//        } else if (ptype == float.class || ptype == Float.class ||
+//                   ptype == Double.class) {
+//            mt = mt.changeReturnType(double.class);
+//        } else if (ptype == Boolean.class) {
+//            mt = mt.changeReturnType(boolean.class);
+//        } else if (ptype == Character.class) {
+//            mt = mt.changeReturnType(char.class);
+//        }
+
+        Class<?> itype = mt.returnType();
+
+        if (itype != ptype) {
+            mh = explicitCastArguments(mh, mt);
+        }
+
+        boolean handled = false;
+        int flags = fs.flags;
+        int width = fs.width;
+        int precision = fs.precision;
+        Character conv = fs.dt ? 't' : fs.c;
+
+        switch (Character.toLowerCase(conv)) {
+            case BOOLEAN -> {
+                if (itype == boolean.class && precision == -1) {
+                    if (flags == 0 && width == -1 && isPrimitive) {
+                        return null;
+                    }
+
+                    if (validFlags(flags, LEFT_JUSTIFY)) {
+                        handled = true;
+                        mh = filterReturnValue(mh, FIBoolean_MH);
+                    }
+                }
+            }
+            case STRING -> {
+                if (flags == 0 && width == -1 && precision == -1) {
+                    if (isPrimitive || ptype == String.class) {
+                        return null;
+                    } else if (itype.isPrimitive()) {
+                        return mh;
+                    }
+                }
+
+                if (validFlags(flags, LEFT_JUSTIFY) && precision == -1) {
+                    if (itype == String.class) {
+                        handled = true;
+                        mh = filterReturnValue(mh, FIString_MH);
+                    } else if (!itype.isPrimitive()) {
+                        handled = true;
+                        MethodHandle test = FormattableCheck_MH;
+                        test = test.asType(test.type().changeParameterType(0, ptype));
+                        MethodHandle pass = insertArguments(FIFormattable_MH,
+                                0, locale, flags, width, precision);
+                        pass = pass.asType(pass.type().changeParameterType(0, ptype));
+                        MethodHandle fail = ToString_MH;
+                        fail = filterReturnValue(fail, FIString_MH);
+                        fail = fail.asType(fail.type().changeParameterType(0, ptype));
+                        mh = guardWithTest(test, pass, fail);
+                    }
+                }
+            }
+            case CHARACTER -> {
+                if (itype == char.class && precision == -1) {
+                    if (flags == 0 && width == -1) {
+                        return isPrimitive ? null : mh;
+                    }
+
+                    if (validFlags(flags, LEFT_JUSTIFY)) {
+                        handled = true;
+                        mh = filterReturnValue(mh, FICharacter_MH);
+                    }
+                }
+            }
+            case DECIMAL_INTEGER -> {
+                if ((itype == int.class || itype == long.class) && precision == -1) {
+                    if (itype == int.class) {
+                        mh = explicitCastArguments(mh,
+                                mh.type().changeReturnType(long.class));
+                    }
+
+                    if (flags == 0 && isGenericDFS && width == -1) {
+                        return mh;
+                    } else if (validFlags(flags, PLUS | LEADING_SPACE |
+                                                 ZERO_PAD | GROUP |
+                                                 PARENTHESES)) {
+                        handled = true;
+                        int zeroPad = isFlag(flags, ZERO_PAD) ? width : -1;
+                        char sign = isFlag(flags, PLUS)          ? '+' :
+                                    isFlag(flags, LEADING_SPACE) ? ' ' : '\0';
+                        boolean parentheses = isFlag(flags, PARENTHESES);
+                        int groupSize = isFlag(flags, GROUP) ?
+                                groupSize(locale, dfs) : 0;
+                        mh = filterReturnValue(mh,
+                                insertArguments(FIDecimal_MH, 0, dfs, zeroPad,
+                                        sign, parentheses, groupSize));
+                    }
+                }
+            }
+            case OCTAL_INTEGER -> {
+                if ((itype == int.class || itype == long.class) &&
+                         precision == -1 &&
+                         validFlags(flags, ZERO_PAD | ALTERNATE)) {
+                    handled = true;
+
+                    if (itype == int.class) {
+                        mh = filterReturnValue(mh, ToLong_MH);
+                    }
+
+                    int zeroPad = isFlag(flags, ZERO_PAD) ? width : -1;
+                    boolean hasPrefix = isFlag(flags, ALTERNATE);
+                    mh = filterReturnValue(mh,
+                            insertArguments(FIOctal_MH, 0, zeroPad, hasPrefix));
+                }
+            }
+            case HEXADECIMAL_INTEGER -> {
+                if ((itype == int.class || itype == long.class) &&
+                        precision == -1 &&
+                        validFlags(flags, ZERO_PAD | ALTERNATE)) {
+                    handled = true;
+
+                    if (itype == int.class) {
+                        mh = filterReturnValue(mh, ToLong_MH);
+                    }
+
+                    int zeroPad = isFlag(flags, ZERO_PAD) ? width : -1;
+                    boolean hasPrefix = isFlag(flags, ALTERNATE);
+                    mh = filterReturnValue(mh,
+                            insertArguments(FIHexadecimal_MH, 0, zeroPad, hasPrefix));
+                }
+            }
+            default -> {
+                // pass thru
+            }
+        }
+
+        if (handled) {
+            if (!isPrimitive) {
+                MethodHandle test = NullCheck_MH.asType(
+                        NullCheck_MH.type().changeParameterType(0, ptype));
+                MethodHandle pass = dropArguments(FINull_MH, 0, ptype);
+                mh = guardWithTest(test, pass, mh);
+            }
+
+            if (0 < width) {
+                if (isFlag(flags, LEFT_JUSTIFY)) {
+                    mh = filterReturnValue(mh,
+                            insertArguments(FIFillRight_MH, 0, width));
+                } else {
+                    mh = filterReturnValue(mh,
+                            insertArguments(FIFillLeft_MH, 0, width));
+                }
+            }
+
+            if (!isFlag(flags, UPPERCASE)) {
+                return mh;
+            }
+        }
+
+        mh = insertArguments(FIFormatSpecifier_MH, 0, fs, locale);
+        mh = mh.asType(mh.type().changeParameterType(0, ptype));
+
+        return mh;
+    }
+
+    /**
+     * Construct concat {@link MethodHandle} for based on format.
+     *
+     * @param fsa  list of specifiers
+     *
+     * @return concat {@link MethodHandle} for based on format
+     */
+    private MethodHandle buildFilters(List<FormatString> fsa,
+                                      List<String> segments,
+                                      MethodHandle[] filters) {
+        MethodHandle mh = null;
+        int iParam = 0;
+        StringBuilder segment = new StringBuilder();
+
+        for (FormatString fs : fsa) {
+            int index = fs.index();
+
+            switch (index) {
+                case -2:  // fixed string, "%n", or "%%"
+                    String string = fs.toString();
+
+                    if ("%%".equals(string)) {
+                        segment.append('%');
+                    } else if ("%n".equals(string)) {
+                        segment.append(System.lineSeparator());
+                    } else {
+                        segment.append(string);
+                    }
+                    break;
+                case 0:  // ordinary index
+                    segments.add(segment.toString());
+                    segment.setLength(0);
+
+                    if (iParam < ptypes.length) {
+                        Class<?> ptype = ptypes[iParam];
+                        filters[iParam++] = formatSpecifier((FormatSpecifier)fs, ptype);
+                    } else {
+                        throw new MissingFormatArgumentException(fs.toString());
+                    }
+                    break;
+                case -1:  // relative index
+                default:  // explicit index
+                    throw new IllegalFormatFlagsException("Indexing not allowed: " + fs.toString());
+            }
+        }
+
+        segments.add(segment.toString());
+
+        return mh;
+    }
+
+    /**
+     * Build a {@link MethodHandle} to format arguments.
+     *
+     * @return new {@link MethodHandle} to format arguments
+     */
+    MethodHandle build() {
+        List<String> segments = new ArrayList<>();
+        MethodHandle[] filters = new MethodHandle[ptypes.length];
+        buildFilters(Formatter.parse(format), segments, filters);
+        Class<?>[] ftypes = new Class<?>[filters.length];
+
+        for (int i = 0; i < filters.length; i++) {
+            MethodHandle filter = filters[i];
+            ftypes[i] = filter == null ? ptypes[i] : filter.type().returnType();
+        }
+
+        try {
+            MethodHandle mh = StringConcatFactory.makeConcatWithTemplate(segments,
+                    List.of(ftypes));
+            mh = filterArguments(mh, 0, filters);
+
+            return mh;
+        } catch (StringConcatException ex) {
+            throw new AssertionError("concat fail", ex);
+        }
+    }
+}

src/java.base/share/classes/jdk/internal/access/JavaLangAccess.java

@@ -45,6 +45,7 @@ import java.util.concurrent.ConcurrentHashMap;
 import java.util.concurrent.RejectedExecutionException;
 import java.util.stream.Stream;
 
+import jdk.internal.javac.PreviewFeature;
 import jdk.internal.misc.CarrierThreadLocal;
 import jdk.internal.module.ServicesCatalog;
 import jdk.internal.reflect.ConstantPool;
@@ -420,6 +421,24 @@ public interface JavaLangAccess {
      */
     long stringConcatMix(long lengthCoder, String constant);
 
+   /**
+    * Get the coder for the supplied character.
+    */
+   @PreviewFeature(feature=PreviewFeature.Feature.STRING_TEMPLATES)
+   long stringConcatCoder(char value);
+
+   /**
+    * Update lengthCoder for StringBuilder.
+    */
+   @PreviewFeature(feature=PreviewFeature.Feature.STRING_TEMPLATES)
+   long stringBuilderConcatMix(long lengthCoder, StringBuilder sb);
+
+    /**
+     * Prepend StringBuilder content.
+     */
+    @PreviewFeature(feature=PreviewFeature.Feature.STRING_TEMPLATES)
+   long stringBuilderConcatPrepend(long lengthCoder, byte[] buf, StringBuilder sb);
+
     /**
      * Join strings
      */

src/java.base/share/classes/jdk/internal/access/JavaTemplateAccess.java

@@ -0,0 +1,78 @@
+/*
+ * Copyright (c) 2023, Oracle and/or its affiliates. All rights reserved.
+ * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
+ *
+ * This code is free software; you can redistribute it and/or modify it
+ * under the terms of the GNU General Public License version 2 only, as
+ * published by the Free Software Foundation.  Oracle designates this
+ * particular file as subject to the "Classpath" exception as provided
+ * by Oracle in the LICENSE file that accompanied this code.
+ *
+ * This code is distributed in the hope that it will be useful, but WITHOUT
+ * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
+ * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
+ * version 2 for more details (a copy is included in the LICENSE file that
+ * accompanied this code).
+ *
+ * You should have received a copy of the GNU General Public License version
+ * 2 along with this work; if not, write to the Free Software Foundation,
+ * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
+ *
+ * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
+ * or visit www.oracle.com if you need additional information or have any
+ * questions.
+ */
+
+package jdk.internal.access;
+
+import java.util.List;
+
+public interface JavaTemplateAccess {
+
+    /**
+     * Returns a StringTemplate composed from fragments and values.
+     *
+     * @implSpec The {@code fragments} list size must be one more that the
+     * {@code values} list size.
+     *
+     * @param fragments list of string fragments
+     * @param values    list of expression values
+     *
+     * @return StringTemplate composed from fragments and values
+     *
+     * @throws IllegalArgumentException if fragments list size is not one more
+     *         than values list size
+     * @throws NullPointerException if fragments is null or values is null or if any fragment is null.
+     *
+     * @implNote Contents of both lists are copied to construct immutable lists.
+     */
+    StringTemplate of(List<String> fragments, List<?> values);
+
+    /**
+     * Creates a string that interleaves the elements of values between the
+     * elements of fragments.
+     *
+     * @param fragments  list of String fragments
+     * @param values     list of expression values
+     *
+     * @return String interpolation of fragments and values
+     */
+    String interpolate(List<String> fragments, List<?> values);
+
+    /**
+     * Combine one or more {@link StringTemplate StringTemplates} to produce a combined {@link StringTemplate}.
+     * {@snippet :
+     * StringTemplate st = StringTemplate.combine("\{a}", "\{b}", "\{c}");
+     * assert st.interpolate().equals("\{a}\{b}\{c}");
+     * }
+     *
+     * @param sts  zero or more {@link StringTemplate}
+     *
+     * @return combined {@link StringTemplate}
+     *
+     * @throws NullPointerException if sts is null or if any element of sts is null
+     */
+    StringTemplate combine(StringTemplate... sts);
+
+}
+

src/java.base/share/classes/jdk/internal/access/SharedSecrets.java

@@ -89,6 +89,7 @@ public class SharedSecrets {
     private static JavaSecuritySpecAccess javaSecuritySpecAccess;
     private static JavaxCryptoSealedObjectAccess javaxCryptoSealedObjectAccess;
     private static JavaxCryptoSpecAccess javaxCryptoSpecAccess;
+    private static JavaTemplateAccess javaTemplateAccess;
 
     public static void setJavaUtilCollectionAccess(JavaUtilCollectionAccess juca) {
         javaUtilCollectionAccess = juca;
@@ -516,6 +517,21 @@ public class SharedSecrets {
         return access;
     }
 
+    public static void setJavaTemplateAccess(JavaTemplateAccess jta) {
+        javaTemplateAccess = jta;
+    }
+
+    public static JavaTemplateAccess getJavaTemplateAccess() {
+        var access = javaTemplateAccess;
+        if (access == null) {
+            try {
+                Class.forName("java.lang.runtime.TemplateSupport", true, null);
+                access = javaTemplateAccess;
+            } catch (ClassNotFoundException e) {}
+        }
+        return access;
+    }
+
     private static void ensureClassInitialized(Class<?> c) {
         try {
             MethodHandles.lookup().ensureInitialized(c);

src/java.base/share/classes/jdk/internal/javac/PreviewFeature.java

@@ -72,6 +72,8 @@ public @interface PreviewFeature {
         VIRTUAL_THREADS,
         @JEP(number=442, title="Foreign Function & Memory API", status="Third Preview")
         FOREIGN,
+        @JEP(number=430, title="String Templates", status="First Preview")
+        STRING_TEMPLATES,
         /**
          * A key for testing.
          */

src/java.base/share/classes/jdk/internal/util/FormatConcatItem.java

@@ -0,0 +1,58 @@
+/*
+ * Copyright (c) 2023, Oracle and/or its affiliates. All rights reserved.
+ * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
+ *
+ * This code is free software; you can redistribute it and/or modify it
+ * under the terms of the GNU General Public License version 2 only, as
+ * published by the Free Software Foundation.  Oracle designates this
+ * particular file as subject to the "Classpath" exception as provided
+ * by Oracle in the LICENSE file that accompanied this code.
+ *
+ * This code is distributed in the hope that it will be useful, but WITHOUT
+ * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
+ * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
+ * version 2 for more details (a copy is included in the LICENSE file that
+ * accompanied this code).
+ *
+ * You should have received a copy of the GNU General Public License version
+ * 2 along with this work; if not, write to the Free Software Foundation,
+ * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
+ *
+ * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
+ * or visit www.oracle.com if you need additional information or have any
+ * questions.
+ */
+
+package jdk.internal.util;
+
+/**
+ * Implementations of this class provide information necessary to
+ * assist {@link java.lang.invoke.StringConcatFactory} perform optimal
+ * insertion.
+ *
+ * @since 21
+ *
+ * Warning: This class is part of PreviewFeature.Feature.STRING_TEMPLATES.
+ *          Do not rely on its availability.
+ */
+public interface FormatConcatItem {
+    /**
+     * Calculate the length of the insertion.
+     *
+     * @param lengthCoder current value of the length + coder
+     * @return adjusted value of the length + coder
+     */
+    long mix(long lengthCoder);
+
+    /**
+     * Insert content into buffer prior to the current length.
+     *
+     * @param lengthCoder current value of the length + coder
+     * @param buffer      buffer to append to
+     *
+     * @return adjusted value of the length + coder
+     *
+     * @throws Throwable if fails to prepend value (unusual).
+     */
+    long prepend(long lengthCoder, byte[] buffer) throws Throwable;
+}

src/jdk.compiler/share/classes/com/sun/source/tree/ClassTree.java

@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 2005, 2021, Oracle and/or its affiliates. All rights reserved.
+ * Copyright (c) 2005, 2023, Oracle and/or its affiliates. All rights reserved.
  * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
  *
  * This code is free software; you can redistribute it and/or modify it
@@ -25,7 +25,6 @@
 
 package com.sun.source.tree;
 
-import java.util.Collections;
 import java.util.List;
 import javax.lang.model.element.Name;
 

src/jdk.compiler/share/classes/com/sun/source/tree/StringTemplateTree.java

@@ -0,0 +1,58 @@
+/*
+ * Copyright (c) 2023, Oracle and/or its affiliates. All rights reserved.
+ * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
+ *
+ * This code is free software; you can redistribute it and/or modify it
+ * under the terms of the GNU General Public License version 2 only, as
+ * published by the Free Software Foundation.  Oracle designates this
+ * particular file as subject to the "Classpath" exception as provided
+ * by Oracle in the LICENSE file that accompanied this code.
+ *
+ * This code is distributed in the hope that it will be useful, but WITHOUT
+ * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
+ * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
+ * version 2 for more details (a copy is included in the LICENSE file that
+ * accompanied this code).
+ *
+ * You should have received a copy of the GNU General Public License version
+ * 2 along with this work; if not, write to the Free Software Foundation,
+ * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
+ *
+ * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
+ * or visit www.oracle.com if you need additional information or have any
+ * questions.
+ */
+
+package com.sun.source.tree;
+
+import java.util.List;
+
+import jdk.internal.javac.PreviewFeature;
+
+/**
+ * A tree node for a string template expression.
+ *
+ */
+@PreviewFeature(feature=PreviewFeature.Feature.STRING_TEMPLATES, reflective=true)
+public interface StringTemplateTree extends ExpressionTree {
+    /**
+     * Returns templated string processor (may be qualified) or null.
+     *
+     * @return templated string processor
+     */
+    ExpressionTree getProcessor();
+
+    /**
+     * Returns string fragments.
+     *
+     * @return string fragments
+     */
+    List<String> getFragments();
+
+    /**
+     * Returns list of expressions.
+     *
+     * @return list of expressions
+     */
+    List<? extends ExpressionTree> getExpressions();
+}

src/jdk.compiler/share/classes/com/sun/source/tree/Tree.java

@@ -175,6 +175,12 @@ public interface Tree {
          */
         INSTANCE_OF(InstanceOfTree.class),
 
+        /**
+         * Used for instances of {@link StringTemplateTree}.
+         */
+        @PreviewFeature(feature=PreviewFeature.Feature.STRING_TEMPLATES, reflective=true)
+        TEMPLATE(StringTemplateTree.class),
+
         /**
          * Used for instances of {@link LabeledStatementTree}.
          */

src/jdk.compiler/share/classes/com/sun/source/tree/TreeVisitor.java

@@ -259,6 +259,15 @@ public interface TreeVisitor<R,P> {
      */
     R visitLiteral(LiteralTree node, P p);
 
+    /**
+     * Visits a StringTemplateTree node.
+     * @param node the node being visited
+     * @param p a parameter value
+     * @return a result value
+     */
+    @PreviewFeature(feature=PreviewFeature.Feature.STRING_TEMPLATES, reflective=true)
+    R visitStringTemplate(StringTemplateTree node, P p);
+
     /**
      * Visits a {@code BindingPatternTree} node.
      * @param node the node being visited

src/jdk.compiler/share/classes/com/sun/source/util/SimpleTreeVisitor.java

@@ -628,6 +628,19 @@ public class SimpleTreeVisitor <R,P> implements TreeVisitor<R,P> {
         return defaultAction(node, p);
     }
 
+    /**
+     * {@inheritDoc} This implementation calls {@code defaultAction}.
+     *
+     * @param node {@inheritDoc}
+     * @param p {@inheritDoc}
+     * @return  the result of {@code defaultAction}
+     */
+    @Override
+    @PreviewFeature(feature=PreviewFeature.Feature.STRING_TEMPLATES, reflective=true)
+    public R visitStringTemplate(StringTemplateTree node, P p) {
+        return defaultAction(node, p);
+    }
+
     /**
      * {@inheritDoc}
      *

src/jdk.compiler/share/classes/com/sun/source/util/TreeScanner.java

@@ -759,6 +759,23 @@ public class TreeScanner<R,P> implements TreeVisitor<R,P> {
         return r;
     }
 
+    /**
+     * {@inheritDoc}
+     *
+     * @implSpec This implementation scans the children in left to right order.
+     *
+     * @param node  {@inheritDoc}
+     * @param p  {@inheritDoc}
+     * @return the result of scanning
+     */
+    @Override
+    @PreviewFeature(feature=PreviewFeature.Feature.STRING_TEMPLATES, reflective=true)
+    public R visitStringTemplate(StringTemplateTree node, P p) {
+        R r = scan(node.getProcessor(), p);
+        r = scanAndReduce(node.getExpressions(), p, r);
+        return r;
+    }
+
     /**
      * {@inheritDoc}
      *

src/jdk.compiler/share/classes/com/sun/tools/javac/code/Preview.java

@@ -211,6 +211,7 @@ public class Preview {
         return switch (feature) {
             case CASE_NULL -> true;
             case PATTERN_SWITCH -> true;
+            case STRING_TEMPLATES -> true;
             case UNCONDITIONAL_PATTERN_IN_INSTANCEOF -> true;
             case RECORD_PATTERNS -> true;
 

src/jdk.compiler/share/classes/com/sun/tools/javac/code/Source.java

@@ -235,6 +235,7 @@ public enum Source {
         CASE_NULL(JDK17, Fragments.FeatureCaseNull, DiagKind.NORMAL),
         PATTERN_SWITCH(JDK17, Fragments.FeaturePatternSwitch, DiagKind.PLURAL),
         REDUNDANT_STRICTFP(JDK17),
+        STRING_TEMPLATES(JDK21, Fragments.FeatureStringTemplates, DiagKind.PLURAL),
         UNCONDITIONAL_PATTERN_IN_INSTANCEOF(JDK19, Fragments.FeatureUnconditionalPatternsInInstanceof, DiagKind.PLURAL),
         RECORD_PATTERNS(JDK19, Fragments.FeatureDeconstructionPatterns, DiagKind.PLURAL),
         WARN_ON_ILLEGAL_UTF8(MIN, JDK21),

src/jdk.compiler/share/classes/com/sun/tools/javac/code/Symtab.java

@@ -174,6 +174,7 @@ public class Symtab {
     public final Type serializedLambdaType;
     public final Type varHandleType;
     public final Type methodHandleType;
+    public final Type methodHandlesType;
     public final Type methodHandleLookupType;
     public final Type methodTypeType;
     public final Type nativeHeaderType;
@@ -234,6 +235,12 @@ public class Symtab {
     public final Type objectStreamExceptionType;
     public final Type externalizableType;
 
+    // For string templates
+    public final Type stringTemplateType;
+    public final Type templateRuntimeType;
+    public final Type processorType;
+    public final Type linkageType;
+
     /** The symbol representing the length field of an array.
      */
     public final VarSymbol lengthVar;
@@ -543,6 +550,7 @@ public class Symtab {
         serializedLambdaType = enterClass("java.lang.invoke.SerializedLambda");
         varHandleType = enterClass("java.lang.invoke.VarHandle");
         methodHandleType = enterClass("java.lang.invoke.MethodHandle");
+        methodHandlesType = enterClass("java.lang.invoke.MethodHandles");
         methodHandleLookupType = enterClass("java.lang.invoke.MethodHandles$Lookup");
         methodTypeType = enterClass("java.lang.invoke.MethodType");
         errorType = enterClass("java.lang.Error");
@@ -610,7 +618,6 @@ public class Symtab {
         ioExceptionType = enterClass("java.io.IOException");
         objectStreamExceptionType = enterClass("java.io.ObjectStreamException");
         externalizableType = enterClass("java.io.Externalizable");
-
         synthesizeEmptyInterfaceIfMissing(autoCloseableType);
         synthesizeEmptyInterfaceIfMissing(cloneableType);
         synthesizeEmptyInterfaceIfMissing(serializableType);
@@ -621,6 +628,12 @@ public class Symtab {
         synthesizeBoxTypeIfMissing(floatType);
         synthesizeBoxTypeIfMissing(voidType);
 
+        // For string templates
+        stringTemplateType = enterClass("java.lang.StringTemplate");
+        templateRuntimeType = enterClass("java.lang.runtime.TemplateRuntime");
+        processorType = enterClass("java.lang.StringTemplate$Processor");
+        linkageType = enterClass("java.lang.StringTemplate$Processor$Linkage");
+
         // Enter a synthetic class that is used to mark internal
         // proprietary classes in ct.sym.  This class does not have a
         // class file.

src/jdk.compiler/share/classes/com/sun/tools/javac/comp/Attr.java

@@ -4984,6 +4984,27 @@ public class Attr extends JCTree.Visitor {
         return (tag == CLASS) ? syms.stringType : syms.typeOfTag[tag.ordinal()];
     }
 
+    public void visitStringTemplate(JCStringTemplate tree) {
+        JCExpression processor = tree.processor;
+        Type resultType = syms.stringTemplateType;
+
+        if (processor != null) {
+            resultType = attribTree(processor, env, new ResultInfo(KindSelector.VAL, Type.noType));
+            resultType = chk.checkProcessorType(processor, resultType, env);
+        }
+
+        Env<AttrContext> localEnv = env.dup(tree, env.info.dup());
+
+        for (JCExpression arg : tree.expressions) {
+            chk.checkNonVoid(arg.pos(), attribExpr(arg, localEnv));
+        }
+
+        tree.type = resultType;
+        result = resultType;
+
+        check(tree, resultType, KindSelector.VAL, resultInfo);
+    }
+
     public void visitTypeIdent(JCPrimitiveTypeTree tree) {
         result = check(tree, syms.typeOfTag[tree.typetag.ordinal()], KindSelector.TYP, resultInfo);
     }

src/jdk.compiler/share/classes/com/sun/tools/javac/comp/Check.java

@@ -117,6 +117,8 @@ public class Check {
     private final Preview preview;
     private final boolean warnOnAnyAccessToMembers;
 
+    public boolean disablePreviewCheck;
+
     // The set of lint options currently in effect. It is initialized
     // from the context, and then is set/reset as needed by Attr as it
     // visits all the various parts of the trees during attribution.
@@ -155,6 +157,8 @@ public class Check {
         target = Target.instance(context);
         warnOnAnyAccessToMembers = options.isSet("warnOnAccessToMembers");
 
+        disablePreviewCheck = false;
+
         Target target = Target.instance(context);
         syntheticNameChar = target.syntheticNameChar();
 
@@ -3793,7 +3797,7 @@ public class Check {
     }
 
     void checkPreview(DiagnosticPosition pos, Symbol other, Symbol s) {
-        if ((s.flags() & PREVIEW_API) != 0 && !preview.participatesInPreview(syms, other, s)) {
+        if ((s.flags() & PREVIEW_API) != 0 && !preview.participatesInPreview(syms, other, s) && !disablePreviewCheck) {
             if ((s.flags() & PREVIEW_REFLECTIVE) == 0) {
                 if (!preview.isEnabled()) {
                     log.error(pos, Errors.IsPreview(s));
@@ -4311,6 +4315,27 @@ public class Check {
         }
     }
 
+    public Type checkProcessorType(JCExpression processor, Type resultType, Env<AttrContext> env) {
+        Type processorType = processor.type;
+        Type interfaceType = types.asSuper(processorType, syms.processorType.tsym);
+
+        if (interfaceType != null) {
+            List<Type> typeArguments = interfaceType.getTypeArguments();
+
+            if (typeArguments.size() == 2) {
+                resultType = typeArguments.head;
+            } else {
+                log.error(DiagnosticFlag.RESOLVE_ERROR, processor.pos,
+                        Errors.ProcessorTypeCannotBeARawType(processorType.tsym));
+            }
+        } else {
+            log.error(DiagnosticFlag.RESOLVE_ERROR, processor.pos,
+                    Errors.NotAProcessorType(processorType.tsym));
+        }
+
+        return resultType;
+    }
+
     public void checkLeaksNotAccessible(Env<AttrContext> env, JCClassDecl check) {
         JCCompilationUnit toplevel = env.toplevel;
 

src/jdk.compiler/share/classes/com/sun/tools/javac/comp/CompileStates.java

@@ -59,10 +59,11 @@ public class CompileStates extends HashMap<Env<AttrContext>, CompileStates.Compi
         ATTR(4),
         FLOW(5),
         TRANSTYPES(6),
-        TRANSPATTERNS(7),
+        TRANSLITERALS(7),
-        UNLAMBDA(8),
+        TRANSPATTERNS(8),
-        LOWER(9),
+        UNLAMBDA(9),
-        GENERATE(10);
+        LOWER(10),
+        GENERATE(11);
 
         CompileState(int value) {
             this.value = value;

src/jdk.compiler/share/classes/com/sun/tools/javac/comp/Flow.java

@@ -1528,6 +1528,30 @@ public class Flow {
             }
         }
 
+        @Override
+        public void visitStringTemplate(JCStringTemplate tree) {
+            JCExpression processor = tree.processor;
+
+            if (processor != null) {
+                scan(processor);
+                Type interfaceType = types.asSuper(processor.type, syms.processorType.tsym);
+
+                if (interfaceType != null) {
+                    List<Type> typeArguments = interfaceType.getTypeArguments();
+
+                    if (typeArguments.size() == 2) {
+                        Type throwType = typeArguments.tail.head;
+
+                        if (throwType != null) {
+                            markThrown(tree, throwType);
+                        }
+                    }
+                }
+            }
+
+            scan(tree.expressions);
+        }
+
         void checkCaughtType(DiagnosticPosition pos, Type exc, List<Type> thrownInTry, List<Type> caughtInTry) {
             if (chk.subset(exc, caughtInTry)) {
                 log.error(pos, Errors.ExceptAlreadyCaught(exc));

src/jdk.compiler/share/classes/com/sun/tools/javac/comp/TransLiterals.java

@@ -0,0 +1,344 @@
+/*
+ * Copyright (c) 2023, Oracle and/or its affiliates. All rights reserved.
+ * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
+ *
+ * This code is free software; you can redistribute it and/or modify it
+ * under the terms of the GNU General Public License version 2 only, as
+ * published by the Free Software Foundation.  Oracle designates this
+ * particular file as subject to the "Classpath" exception as provided
+ * by Oracle in the LICENSE file that accompanied this code.
+ *
+ * This code is distributed in the hope that it will be useful, but WITHOUT
+ * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
+ * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
+ * version 2 for more details (a copy is included in the LICENSE file that
+ * accompanied this code).
+ *
+ * You should have received a copy of the GNU General Public License version
+ * 2 along with this work; if not, write to the Free Software Foundation,
+ * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
+ *
+ * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
+ * or visit www.oracle.com if you need additional information or have any
+ * questions.
+ */
+
+package com.sun.tools.javac.comp;
+
+import com.sun.tools.javac.code.Flags;
+import com.sun.tools.javac.code.Symbol;
+import com.sun.tools.javac.code.Symbol.ClassSymbol;
+import com.sun.tools.javac.code.Symbol.DynamicMethodSymbol;
+import com.sun.tools.javac.code.Symbol.MethodSymbol;
+import com.sun.tools.javac.code.Symbol.VarSymbol;
+import com.sun.tools.javac.code.Symtab;
+import com.sun.tools.javac.code.Type;
+import com.sun.tools.javac.code.Type.*;
+import com.sun.tools.javac.code.Types;
+import com.sun.tools.javac.jvm.PoolConstant.LoadableConstant;
+import com.sun.tools.javac.tree.JCTree;
+import com.sun.tools.javac.tree.JCTree.*;
+import com.sun.tools.javac.tree.TreeInfo;
+import com.sun.tools.javac.tree.TreeMaker;
+import com.sun.tools.javac.tree.TreeTranslator;
+import com.sun.tools.javac.util.Context;
+import com.sun.tools.javac.util.JCDiagnostic.DiagnosticPosition;
+import com.sun.tools.javac.util.List;
+import com.sun.tools.javac.util.Name;
+import com.sun.tools.javac.util.Names;
+
+import java.util.Iterator;
+
+/** This pass translates constructed literals (string templates, ...) to conventional Java.
+ *
+ *  <p><b>This is NOT part of any supported API.
+ *  If you write code that depends on this, you do so at your own risk.
+ *  This code and its internal interfaces are subject to change or
+ *  deletion without notice.</b>
+ */
+public final class TransLiterals extends TreeTranslator {
+    /**
+     * The context key for the TransTypes phase.
+     */
+    protected static final Context.Key<TransLiterals> transLiteralsKey = new Context.Key<>();
+
+    /**
+     * Get the instance for this context.
+     */
+    public static TransLiterals instance(Context context) {
+        TransLiterals instance = context.get(transLiteralsKey);
+        if (instance == null)
+            instance = new TransLiterals(context);
+        return instance;
+    }
+
+    private final Symtab syms;
+    private final Resolve rs;
+    private final Types types;
+    private final Operators operators;
+    private final Names names;
+    private TreeMaker make = null;
+    private Env<AttrContext> env = null;
+    private ClassSymbol currentClass = null;
+    private MethodSymbol currentMethodSym = null;
+
+    protected TransLiterals(Context context) {
+        context.put(transLiteralsKey, this);
+        syms = Symtab.instance(context);
+        rs = Resolve.instance(context);
+        make = TreeMaker.instance(context);
+        types = Types.instance(context);
+        operators = Operators.instance(context);
+        names = Names.instance(context);
+    }
+
+    JCExpression makeLit(Type type, Object value) {
+        return make.Literal(type.getTag(), value).setType(type.constType(value));
+    }
+
+    JCExpression makeString(String string) {
+        return makeLit(syms.stringType, string);
+    }
+
+    List<JCExpression> makeStringList(List<String> strings) {
+        List<JCExpression> exprs = List.nil();
+        for (String string : strings) {
+            exprs = exprs.append(makeString(string));
+        }
+        return exprs;
+    }
+
+    JCBinary makeBinary(JCTree.Tag optag, JCExpression lhs, JCExpression rhs) {
+        JCBinary tree = make.Binary(optag, lhs, rhs);
+        tree.operator = operators.resolveBinary(tree, optag, lhs.type, rhs.type);
+        tree.type = tree.operator.type.getReturnType();
+        return tree;
+    }
+
+    MethodSymbol lookupMethod(DiagnosticPosition pos, Name name, Type qual, List<Type> args) {
+        return rs.resolveInternalMethod(pos, env, qual, name, args, List.nil());
+    }
+
+    @Override
+    public void visitClassDef(JCClassDecl tree) {
+        ClassSymbol prevCurrentClass = currentClass;
+        try {
+            currentClass = tree.sym;
+            super.visitClassDef(tree);
+        } finally {
+            currentClass = prevCurrentClass;
+        }
+    }
+
+    @Override
+    public void visitMethodDef(JCMethodDecl tree) {
+        MethodSymbol prevMethodSym = currentMethodSym;
+        try {
+            currentMethodSym = tree.sym;
+            super.visitMethodDef(tree);
+        } finally {
+            currentMethodSym = prevMethodSym;
+        }
+    }
+
+    final class TransStringTemplate {
+        final JCStringTemplate tree;
+        final JCExpression processor;
+        final List<String> fragments;
+        final List<JCExpression> expressions;
+        final List<Type> expressionTypes;
+        final boolean useValuesList;
+
+        TransStringTemplate(JCStringTemplate tree) {
+            this.tree = tree;
+            this.processor = tree.processor;
+            this.fragments = tree.fragments;
+            this.expressions = translate(tree.expressions);
+            this.expressionTypes = expressions.stream()
+                    .map(arg -> arg.type == syms.botType ? syms.objectType : arg.type)
+                    .collect(List.collector());
+            int slots = expressionTypes.stream()
+                    .mapToInt(t -> types.isSameType(t, syms.longType) ||
+                            types.isSameType(t, syms.doubleType) ? 2 : 1).sum();
+            this.useValuesList = 200 < slots; // StringConcatFactory.MAX_INDY_CONCAT_ARG_SLOTS
+         }
+
+        JCExpression concatExpression(List<String> fragments, List<JCExpression> expressions) {
+            JCExpression expr = null;
+            Iterator<JCExpression> iterator = expressions.iterator();
+            for (String fragment : fragments) {
+                expr = expr == null ? makeString(fragment)
+                        : makeBinary(Tag.PLUS, expr, makeString(fragment));
+                if (iterator.hasNext()) {
+                    JCExpression expression = iterator.next();
+                    Type expressionType = expression.type;
+                    expr = makeBinary(Tag.PLUS, expr, expression.setType(expressionType));
+                }
+            }
+            return expr;
+        }
+
+        JCExpression bsmCall(Name name, Name bootstrapName, Type type,
+                             List<JCExpression> args,
+                             List<Type> argTypes,
+                             List<LoadableConstant> staticArgValues,
+                             List<Type> staticArgsTypes) {
+            Symbol bsm = rs.resolveQualifiedMethod(tree.pos(), env,
+                    syms.templateRuntimeType, bootstrapName, staticArgsTypes, List.nil());
+            MethodType indyType = new MethodType(argTypes, type, List.nil(), syms.methodClass);
+            DynamicMethodSymbol dynSym = new DynamicMethodSymbol(
+                    name,
+                    syms.noSymbol,
+                    ((MethodSymbol)bsm).asHandle(),
+                    indyType,
+                    staticArgValues.toArray(new LoadableConstant[0])
+            );
+            JCFieldAccess qualifier = make.Select(make.Type(syms.processorType), dynSym.name);
+            qualifier.sym = dynSym;
+            qualifier.type = type;
+            JCMethodInvocation apply = make.Apply(List.nil(), qualifier, args);
+            apply.type = type;
+            return apply;
+        }
+
+        JCExpression processCall(JCExpression stringTemplate) {
+            MethodSymbol appyMeth = lookupMethod(tree.pos(), names.process,
+                    syms.processorType, List.of(syms.stringTemplateType));
+            JCExpression applySelect = make.Select(processor, appyMeth);
+            JCExpression process = make.Apply(null, applySelect, List.of(stringTemplate))
+                    .setType(syms.objectType);
+            JCTypeCast cast = make.TypeCast(tree.type, process);
+            return cast;
+        }
+
+        JCExpression newStringTemplate() {
+            List<LoadableConstant> staticArgValues = List.nil();
+            List<Type> staticArgsTypes =
+                    List.of(syms.methodHandleLookupType, syms.stringType,
+                            syms.methodTypeType);
+            if (useValuesList) {
+                JCNewArray fragmentArray = make.NewArray(make.Type(syms.stringType),
+                        List.nil(), makeStringList(fragments));
+                fragmentArray.type = new ArrayType(syms.stringType, syms.arrayClass);
+                JCNewArray valuesArray = make.NewArray(make.Type(syms.objectType),
+                        List.nil(), expressions);
+                valuesArray.type = new ArrayType(syms.objectType, syms.arrayClass);
+                return bsmCall(names.process, names.newLargeStringTemplate, syms.stringTemplateType,
+                        List.of(fragmentArray, valuesArray),
+                        List.of(fragmentArray.type, valuesArray.type),
+                        staticArgValues, staticArgsTypes);
+            } else {
+                for (String fragment : fragments) {
+                    staticArgValues = staticArgValues.append(LoadableConstant.String(fragment));
+                    staticArgsTypes = staticArgsTypes.append(syms.stringType);
+                }
+                return bsmCall(names.process, names.newStringTemplate, syms.stringTemplateType,
+                        expressions, expressionTypes, staticArgValues, staticArgsTypes);
+            }
+        }
+
+        JCExpression bsmProcessCall() {
+            List<JCExpression> args = expressions.prepend(processor);
+            List<Type> argTypes = expressionTypes.prepend(processor.type);
+            VarSymbol processorSym = (VarSymbol)TreeInfo.symbol(processor);
+            List<LoadableConstant> staticArgValues = List.of(processorSym.asMethodHandle(true));
+            List<Type> staticArgsTypes =
+                    List.of(syms.methodHandleLookupType, syms.stringType,
+                            syms.methodTypeType, syms.methodHandleType);
+            for (String fragment : fragments) {
+                staticArgValues = staticArgValues.append(LoadableConstant.String(fragment));
+                staticArgsTypes = staticArgsTypes.append(syms.stringType);
+            }
+            return bsmCall(names.process, names.processStringTemplate, tree.type,
+                    args, argTypes, staticArgValues, staticArgsTypes);
+        }
+
+        boolean isNamedProcessor(Name name) {
+            if (processor instanceof JCIdent ident && ident.sym instanceof VarSymbol varSym) {
+                if (varSym.flags() == (Flags.PUBLIC | Flags.FINAL | Flags.STATIC) &&
+                        varSym.name == name &&
+                        types.isSameType(varSym.owner.type, syms.stringTemplateType)) {
+                    return true;
+                }
+            }
+            return false;
+        }
+
+        boolean isLinkageProcessor() {
+            return processor != null &&
+                   !useValuesList &&
+                   types.isSubtype(processor.type, syms.linkageType) &&
+                   processor.type.isFinal() &&
+                   TreeInfo.symbol(processor) instanceof VarSymbol varSymbol &&
+                   varSymbol.isStatic() &&
+                   varSymbol.isFinal();
+        }
+
+        JCExpression visit() {
+            JCExpression result;
+            make.at(tree.pos);
+
+            if (processor == null || isNamedProcessor(names.RAW)) {
+                result = newStringTemplate();
+            } else if (isNamedProcessor(names.STR)) {
+                result = concatExpression(fragments, expressions);
+            } else if (isLinkageProcessor()) {
+                result = bsmProcessCall();
+            } else {
+                result = processCall(newStringTemplate());
+            }
+
+            return result;
+        }
+    }
+
+    public void visitStringTemplate(JCStringTemplate tree) {
+        int prevPos = make.pos;
+        try {
+            tree.processor = translate(tree.processor);
+            tree.expressions = translate(tree.expressions);
+
+            TransStringTemplate transStringTemplate = new TransStringTemplate(tree);
+
+            result = transStringTemplate.visit();
+        } catch (Throwable ex) {
+            ex.printStackTrace();
+            throw ex;
+        } finally {
+            make.at(prevPos);
+        }
+    }
+
+    public void visitVarDef(JCVariableDecl tree) {
+        MethodSymbol prevMethodSym = currentMethodSym;
+        try {
+            tree.mods = translate(tree.mods);
+            tree.vartype = translate(tree.vartype);
+            if (currentMethodSym == null) {
+                // A class or instance field initializer.
+                currentMethodSym =
+                        new MethodSymbol((tree.mods.flags& Flags.STATIC) | Flags.BLOCK,
+                                names.empty, null,
+                                currentClass);
+            }
+            if (tree.init != null) tree.init = translate(tree.init);
+            result = tree;
+        } finally {
+            currentMethodSym = prevMethodSym;
+        }
+    }
+
+    public JCTree translateTopLevelClass(Env<AttrContext> env, JCTree cdef, TreeMaker make) {
+        try {
+            this.make = make;
+            this.env = env;
+            translate(cdef);
+        } finally {
+            this.make = null;
+            this.env = null;
+        }
+
+        return cdef;
+    }
+
+}

src/jdk.compiler/share/classes/com/sun/tools/javac/comp/TransTypes.java

@@ -838,6 +838,13 @@ public class TransTypes extends TreeTranslator {
         }
     }
 
+    public void visitStringTemplate(JCStringTemplate tree) {
+        tree.expressions = tree.expressions.stream()
+                .map(e -> translate(e, erasure(e.type))).collect(List.collector());
+        tree.type = erasure(tree.type);
+        result = tree;
+    }
+
     public void visitSelect(JCFieldAccess tree) {
         Type t = types.skipTypeVars(tree.selected.type, false);
         if (t.isCompound()) {

src/jdk.compiler/share/classes/com/sun/tools/javac/comp/TypeEnter.java

@@ -25,22 +25,23 @@
 
 package com.sun.tools.javac.comp;
 
-import java.util.ArrayList;
 import java.util.HashSet;
 import java.util.Set;
 import java.util.function.BiConsumer;
-import java.util.stream.Collectors;
 
 import javax.tools.JavaFileObject;
 
 import com.sun.tools.javac.code.*;
 import com.sun.tools.javac.code.Lint.LintCategory;
 import com.sun.tools.javac.code.Scope.ImportFilter;
+import com.sun.tools.javac.code.Scope.ImportScope;
 import com.sun.tools.javac.code.Scope.NamedImportScope;
 import com.sun.tools.javac.code.Scope.StarImportScope;
 import com.sun.tools.javac.code.Scope.WriteableScope;
 import com.sun.tools.javac.code.Source.Feature;
 import com.sun.tools.javac.comp.Annotate.AnnotationTypeMetadata;
+import com.sun.tools.javac.parser.Parser;
+import com.sun.tools.javac.parser.ParserFactory;
 import com.sun.tools.javac.tree.*;
 import com.sun.tools.javac.util.*;
 import com.sun.tools.javac.util.DefinedBy.Api;
@@ -113,6 +114,7 @@ public class TypeEnter implements Completer {
     private final Lint lint;
     private final TypeEnvs typeEnvs;
     private final Dependencies dependencies;
+    private final ParserFactory parserFactory;
     private final Preview preview;
 
     public static TypeEnter instance(Context context) {
@@ -141,6 +143,7 @@ public class TypeEnter implements Completer {
         lint = Lint.instance(context);
         typeEnvs = TypeEnvs.instance(context);
         dependencies = Dependencies.instance(context);
+        parserFactory = ParserFactory.instance(context);
         preview = Preview.instance(context);
         Source source = Source.instance(context);
         allowDeprecationOnImport = Feature.DEPRECATION_ON_IMPORT.allowedInSource(source);
@@ -326,6 +329,40 @@ public class TypeEnter implements Completer {
                 sym.owner.complete();
         }
 
+        private void importJavaLang(JCCompilationUnit tree, Env<AttrContext> env, ImportFilter typeImportFilter) {
+            // Import-on-demand java.lang.
+            PackageSymbol javaLang = syms.enterPackage(syms.java_base, names.java_lang);
+            if (javaLang.members().isEmpty() && !javaLang.exists()) {
+                log.error(Errors.NoJavaLang);
+                throw new Abort();
+            }
+            importAll(make.at(tree.pos()).Import(make.Select(make.QualIdent(javaLang.owner), javaLang), false),
+                javaLang, env);
+        }
+
+        private void staticImports(JCCompilationUnit tree, Env<AttrContext> env, ImportFilter staticImportFilter) {
+             if (preview.isEnabled() && preview.isPreview(Feature.STRING_TEMPLATES)) {
+                Lint prevLint = chk.setLint(lint.suppress(LintCategory.DEPRECATION, LintCategory.REMOVAL, LintCategory.PREVIEW));
+                boolean prevPreviewCheck = chk.disablePreviewCheck;
+
+                try {
+                    chk.disablePreviewCheck = true;
+                    String autoImports = """
+                            import static java.lang.StringTemplate.STR;
+                            """;
+                    Parser parser = parserFactory.newParser(autoImports, false, false, false, false);
+                    JCCompilationUnit importTree = parser.parseCompilationUnit();
+
+                    for (JCImport imp : importTree.getImports()) {
+                        doImport(imp);
+                    }
+                } finally {
+                    chk.setLint(prevLint);
+                    chk.disablePreviewCheck = prevPreviewCheck;
+                }
+            }
+        }
+
         private void resolveImports(JCCompilationUnit tree, Env<AttrContext> env) {
             if (tree.starImportScope.isFilled()) {
                 // we must have already processed this toplevel
@@ -348,14 +385,8 @@ public class TypeEnter implements Completer {
                         (origin, sym) -> sym.kind == TYP &&
                                          chk.importAccessible(sym, packge);
 
-                // Import-on-demand java.lang.
+                importJavaLang(tree, env, typeImportFilter);
-                PackageSymbol javaLang = syms.enterPackage(syms.java_base, names.java_lang);
+                staticImports(tree, env, staticImportFilter);
-                if (javaLang.members().isEmpty() && !javaLang.exists()) {
-                    log.error(Errors.NoJavaLang);
-                    throw new Abort();
-                }
-                importAll(make.at(tree.pos()).Import(make.Select(make.QualIdent(javaLang.owner), javaLang), false),
-                    javaLang, env);
 
                 JCModuleDecl decl = tree.getModuleDecl();
 

src/jdk.compiler/share/classes/com/sun/tools/javac/main/JavaCompiler.java

@@ -1594,6 +1594,12 @@ public class JavaCompiler {
             env.tree = transTypes.translateTopLevelClass(env.tree, localMake);
             compileStates.put(env, CompileState.TRANSTYPES);
 
+            if (shouldStop(CompileState.TRANSLITERALS))
+                return;
+
+            env.tree = TransLiterals.instance(context).translateTopLevelClass(env, env.tree, localMake);
+            compileStates.put(env, CompileState.TRANSLITERALS);
+
             if (shouldStop(CompileState.TRANSPATTERNS))
                 return;
 

src/jdk.compiler/share/classes/com/sun/tools/javac/parser/JavaTokenizer.java

@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 1999, 2020, Oracle and/or its affiliates. All rights reserved.
+ * Copyright (c) 1999, 2023, Oracle and/or its affiliates. All rights reserved.
  * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
  *
  * This code is free software; you can redistribute it and/or modify it
@@ -38,8 +38,8 @@ import com.sun.tools.javac.util.*;
 import com.sun.tools.javac.util.JCDiagnostic.*;
 
 import java.nio.CharBuffer;
+import java.util.Iterator;
 import java.util.Set;
-import java.util.regex.Pattern;
 
 import static com.sun.tools.javac.parser.Tokens.*;
 import static com.sun.tools.javac.util.LayoutCharacters.EOI;
@@ -62,17 +62,17 @@ public class JavaTokenizer extends UnicodeReader {
     /**
      * Sentinel for non-value.
      */
-    private int NOT_FOUND = -1;
+    private final static int NOT_FOUND = -1;
 
     /**
      * The source language setting. Copied from scanner factory.
      */
-    private Source source;
+    private final Source source;
 
     /**
      * The preview language setting. Copied from scanner factory.
      */
-    private Preview preview;
+    private final Preview preview;
 
     /**
      * The log to be used for error reporting. Copied from scanner factory.
@@ -89,6 +89,26 @@ public class JavaTokenizer extends UnicodeReader {
      */
     private final Names names;
 
+    /**
+     * Origin scanner factory.
+     */
+    protected final ScannerFactory fac;
+
+    /**
+     * Buffer for building literals, used by nextToken().
+     */
+    protected final StringBuilder sb;
+
+    /**
+     * Tokens pending to be read from string template embedded expressions.
+     */
+    protected List<Token> pendingTokens;
+
+    /**
+     * String template fragment ranges; end-endPos pairs.
+     */
+    protected List<Integer> fragmentRanges;
+
     /**
      * The token kind, set by nextToken().
      */
@@ -120,21 +140,21 @@ public class JavaTokenizer extends UnicodeReader {
     protected boolean hasEscapeSequences;
 
     /**
-     * Buffer for building literals, used by nextToken().
+     * true if contains templated string escape sequences, set by nextToken().
      */
-    protected StringBuilder sb;
+    protected boolean isStringTemplate;
 
     /**
-     * Origin scanner factory.
+     * true if errors are pending from embedded expressions.
      */
-    protected ScannerFactory fac;
+    protected boolean hasStringTemplateErrors;
 
     /**
      * The set of lint options currently in effect. It is initialized
      * from the context, and then is set/reset as needed by Attr as it
      * visits all the various parts of the trees during attribution.
      */
-    protected Lint lint;
+    protected final Lint lint;
 
     /**
      * Construct a Java token scanner from the input character buffer.
@@ -149,9 +169,9 @@ public class JavaTokenizer extends UnicodeReader {
     /**
      * Construct a Java token scanner from the input character array.
      *
-     * @param fac     the factory which created this Scanner
+     * @param fac      factory which created this Scanner
-     * @param array   the input character array.
+     * @param array    input character array
-     * @param length  The length of the meaningful content in the array.
+     * @param length   length of the meaningful content in the array
      */
     protected JavaTokenizer(ScannerFactory fac, char[] array, int length) {
         super(fac, array, length);
@@ -163,6 +183,8 @@ public class JavaTokenizer extends UnicodeReader {
         this.preview = fac.preview;
         this.lint = fac.lint;
         this.sb = new StringBuilder(256);
+        this.pendingTokens = List.nil();
+        this.fragmentRanges = List.nil();
     }
 
     /**
@@ -318,19 +340,106 @@ public class JavaTokenizer extends UnicodeReader {
     }
 
     /**
-     * Processes the current character and places in the literal buffer. If the current
+     * Scan the content of a string template expression.
-     * character is a backslash then the next character is validated as a proper
-     * escape character. Conversion of escape sequences takes place at end of nextToken().
      *
-     * @param pos position of the first character in literal.
+     * @param pos     start of literal
+     * @param endPos  start of embedded expression
+     */
+    private void scanEmbeddedExpression(int pos, int endPos) {
+        // If first embedded expression.
+        if (!isStringTemplate) {
+            checkSourceLevel(pos, Feature.STRING_TEMPLATES);
+            fragmentRanges = fragmentRanges.append(pos);
+            isStringTemplate = true;
+        }
+        // Track end of previous fragment.
+        fragmentRanges = fragmentRanges.append(endPos);
+        // Keep backslash and add rest of placeholder.
+        sb.append("{}");
+
+        // Separate tokenizer for the embedded expression.
+        JavaTokenizer tokenizer = new JavaTokenizer(fac, buffer(), length());
+        tokenizer.reset(position());
+
+        // Track brace depth.
+        int braceCount = 0;
+
+        // Accumulate tokens.
+        List<Token> tokens = List.nil();
+
+        // Stash first left brace.
+        Token token = tokenizer.readToken();
+        tokens = tokens.append(token);
+
+        while (isAvailable()) {
+            // Read and stash next token.
+            token = tokenizer.readToken();
+            tokens = tokens.append(token);
+
+            // Intercept errors
+            if (token.kind == TokenKind.ERROR) {
+                // Track start of next fragment.
+                if (isTextBlock) {
+                    reset(length());
+                } else {
+                    skipToEOLN();
+                }
+                hasStringTemplateErrors = true;
+                return;
+            }
+
+            if (token.kind == TokenKind.RBRACE) {
+                // Potential closing brace.
+                if (braceCount == 0) {
+                    break;
+                }
+
+                braceCount--;
+            } else if (token.kind == TokenKind.LBRACE) {
+                // Nesting deeper.
+                braceCount++;
+            } else if (token.kind == TokenKind.STRINGFRAGMENT) {
+                tokens = tokens.appendList(tokenizer.pendingTokens);
+                tokenizer.pendingTokens = List.nil();
+            } else if (token.kind == TokenKind.EOF) {
+                break;
+            }
+        }
+
+        // If no closing brace will be picked up as an unterminated string.
+
+        // Set main tokenizer to continue at next position.
+        int position = tokenizer.position();
+        reset(position);
+
+        // Track start of next fragment.
+        fragmentRanges = fragmentRanges.append(position);
+
+        // Pend the expression tokens after the STRINGFRAGMENT.
+        pendingTokens = pendingTokens.appendList(tokens);
+    }
+
+    /**
+     * Processes the current character and places in the literal buffer. If the current
+     * character is a backslash then the next character is assumed to be a proper
+     * escape character. Actual conversion of escape sequences takes place
+     * during at the end of readToken.
+     *
+     * @param pos          position of the first character in literal.
      */
     private void scanLitChar(int pos) {
+        int backslash = position();
         if (acceptThenPut('\\')) {
             hasEscapeSequences = true;
-
             switch (get()) {
-                case '0': case '1': case '2': case '3':
+                case '0':
-                case '4': case '5': case '6': case '7':
+                case '1':
+                case '2':
+                case '3':
+                case '4':
+                case '5':
+                case '6':
+                case '7':
                     char leadch = get();
                     putThenNext();
 
@@ -370,6 +479,13 @@ public class JavaTokenizer extends UnicodeReader {
                     }
                     break;
 
+                case '{':
+                    scanEmbeddedExpression(pos, backslash);
+                    if (hasStringTemplateErrors) {
+                        return;
+                    }
+                    break;
+
                 default:
                     lexError(position(), Errors.IllegalEscChar);
                     break;
@@ -385,10 +501,10 @@ public class JavaTokenizer extends UnicodeReader {
      * @param pos  position of the first character in literal.
      */
     private void scanString(int pos) {
-        // Assume the best.
-        tk = Tokens.TokenKind.STRINGLITERAL;
         // Track the end of first line for error recovery.
         int firstEOLN = NOT_FOUND;
+        tk = TokenKind.STRINGLITERAL;
+
         // Check for text block delimiter.
         isTextBlock = accept("\"\"\"");
 
@@ -409,7 +525,13 @@ public class JavaTokenizer extends UnicodeReader {
 
             // While characters are available.
             while (isAvailable()) {
-                if (accept("\"\"\"")) {
+                if (hasStringTemplateErrors) {
+                    break;
+                } else if (accept("\"\"\"")) {
+                    if (isStringTemplate && tk == TokenKind.STRINGLITERAL) {
+                        tk = TokenKind.STRINGFRAGMENT;
+                    }
+
                     return;
                 }
 
@@ -433,7 +555,12 @@ public class JavaTokenizer extends UnicodeReader {
 
             // While characters are available.
             while (isAvailable()) {
-                if (accept('\"')) {
+                if (hasStringTemplateErrors) {
+                    break;
+                } else if (accept('\"')) {
+                    if (isStringTemplate && tk == TokenKind.STRINGLITERAL) {
+                        tk = TokenKind.STRINGFRAGMENT;
+                    }
                     return;
                 }
 
@@ -448,10 +575,18 @@ public class JavaTokenizer extends UnicodeReader {
             }
         }
 
-        // String ended without close delimiter sequence.
+        // String ended without close delimiter sequence or has embedded expression errors.
-        lexError(pos, isTextBlock ? Errors.UnclosedTextBlock : Errors.UnclosedStrLit);
+        if (isStringTemplate) {
+            lexError(pos, isTextBlock ? Errors.TextBlockTemplateIsNotWellFormed
+                                      : Errors.StringTemplateIsNotWellFormed);
+            fragmentRanges = List.nil();
+            pendingTokens = List.nil();
+        } else {
+            lexError(pos, isTextBlock ? Errors.UnclosedTextBlock
+                                      : Errors.UnclosedStrLit);
+        }
 
-        if (firstEOLN  != NOT_FOUND) {
+        if (!hasStringTemplateErrors && firstEOLN  != NOT_FOUND) {
             // Reset recovery position to point after text block open delimiter sequence.
             reset(firstEOLN);
         }
@@ -772,11 +907,20 @@ public class JavaTokenizer extends UnicodeReader {
      * Read token (main entrypoint.)
      */
     public Token readToken() {
+        if (pendingTokens.nonEmpty()) {
+            Token token = pendingTokens.head;
+            pendingTokens = pendingTokens.tail;
+            return token;
+        }
+
         sb.setLength(0);
         name = null;
         radix = 0;
         isTextBlock = false;
         hasEscapeSequences = false;
+        isStringTemplate = false;
+        hasStringTemplateErrors = false;
+        fragmentRanges = List.nil();
 
         int pos;
         List<Comment> comments = null;
@@ -971,6 +1115,7 @@ public class JavaTokenizer extends UnicodeReader {
                             lexError(pos, Errors.IllegalLineEndInCharLit);
                         }
 
+                        int errorPos = position();
                         scanLitChar(pos);
 
                         if (accept('\'')) {
@@ -980,7 +1125,6 @@ public class JavaTokenizer extends UnicodeReader {
                         }
                     }
                     break loop;
-
                 case '\"': // (Spec. 3.10)
                     scanString(pos);
                     break loop;
@@ -1017,8 +1161,8 @@ public class JavaTokenizer extends UnicodeReader {
                                 arg = String.format("\\u%04x\\u%04x", (int) hi, (int) lo);
                             } else {
                                 char ch = get();
-                                arg = (32 < ch && ch < 127) ? String.format("%s", ch) :
+                                arg = (32 < ch && ch < 127) ? String.valueOf(ch) :
-                                                              String.format("\\u%04x", (int) ch);
+                                                              "\\u%04x".formatted((int) ch);
                             }
 
                             lexError(pos, Errors.IllegalChar(arg));
@@ -1031,6 +1175,11 @@ public class JavaTokenizer extends UnicodeReader {
 
             int endPos = position();
 
+            // Track end of final fragment.
+            if (isStringTemplate) {
+                fragmentRanges = fragmentRanges.append(endPos);
+            }
+
             if (tk.tag == Token.Tag.DEFAULT) {
                 return new Token(tk, pos, endPos, comments);
             } else  if (tk.tag == Token.Tag.NAMED) {
@@ -1062,6 +1211,11 @@ public class JavaTokenizer extends UnicodeReader {
                     }
                 }
 
+                if (isStringTemplate) {
+                    // Break string into fragments and then return the first of the framents.
+                    return getFragments(string, comments);
+                }
+
                 // Translate escape sequences if present.
                 if (hasEscapeSequences) {
                     try {
@@ -1091,6 +1245,66 @@ public class JavaTokenizer extends UnicodeReader {
         }
     }
 
+    /**
+     * Convert the string into a list of pending tokens to precede embedded
+     * expressions.
+     *
+     * @param string    string to fragment
+     * @param comments  comments for first token
+     *
+     * @return first pending token.
+     */
+    private Token getFragments(String string, List<Comment> comments) {
+        List<Token> tokens = List.nil();
+        Iterator<Integer> rangeIter = fragmentRanges.iterator();
+        for (String fragment : fragment(string)) {
+            fragment = fragment.translateEscapes();
+            int fragmentPos = rangeIter.next();
+            int fragmentEndPos = rangeIter.next();
+            Token token = new StringToken(TokenKind.STRINGFRAGMENT,
+                    fragmentPos, fragmentEndPos, fragment, comments);
+            comments = null;
+            tokens = tokens.append(token);
+        }
+        pendingTokens = tokens.appendList(pendingTokens);
+        Token first = pendingTokens.head;
+        pendingTokens = pendingTokens.tail;
+        return first;
+    }
+
+    /**
+     * Break string template up into fragments. "\{}" indicates where
+     * embedded expressions occur.
+     *
+     * @param string string template
+     *
+     * @return list of fragment strings
+     */
+    List<String> fragment(String string) {
+        List<String> fragments = List.nil();
+        StringBuilder sb = new StringBuilder();
+        int length = string.length();
+        for (int i = 0; i < length; i++) {
+            char ch = string.charAt(i);
+            if (ch != '\\') {
+                sb.append(ch);
+            } else if (i + 2 < length && string.charAt(i + 1) == '{'
+                    && string.charAt(i + 2) == '}') {
+                fragments = fragments.append(sb.toString());
+                sb.setLength(0);
+                i += 2;
+            } else if (i + 1 < length){
+                sb.append('\\');
+                sb.append(string.charAt(i + 1));
+                i++;
+            } else {
+                // Error already reported.
+            }
+        }
+        fragments = fragments.append(sb.toString());
+        return fragments;
+    }
+
     /**
      * Appends a comment to the list of comments preceding the current token.
      *

src/jdk.compiler/share/classes/com/sun/tools/javac/parser/JavacParser.java

@@ -651,6 +651,59 @@ public class JavacParser implements Parser {
         return t;
     }
 
+    /**
+     * StringTemplate =
+     *    [STRINGFRAGMENT] [EmbeddedExpression]
+     *  | STRINGLITERAL
+     *
+     * EmbeddedExpression =
+     *  LBRACE term RBRACE
+     */
+    JCExpression stringTemplate(JCExpression processor) {
+        checkSourceLevel(Feature.STRING_TEMPLATES);
+        // Disable standalone string templates
+        if (processor == null) {
+            log.error(DiagnosticFlag.SYNTAX, token.pos,
+                    Errors.ProcessorMissingFromStringTemplateExpression);
+        }
+        int oldmode = mode;
+        selectExprMode();
+        Token stringToken = token;
+        int pos = stringToken.pos;
+        int endPos = stringToken.endPos;
+        TokenKind kind = stringToken.kind;
+        String string = token.stringVal();
+        List<String> fragments = List.of(string);
+        List<JCExpression> expressions = List.nil();
+        nextToken();
+        if (kind != STRINGLITERAL) {
+            while (token.kind == STRINGFRAGMENT) {
+                stringToken = token;
+                endPos = stringToken.endPos;
+                string = stringToken.stringVal();
+                fragments = fragments.append(string);
+                nextToken();
+             }
+            while (token.pos < endPos && token.kind != DEFAULT && token.kind != ERROR) {
+                accept(LBRACE);
+                JCExpression expression = token.kind == RBRACE ? F.at(pos).Literal(TypeTag.BOT, null)
+                                                               : term(EXPR);
+                expressions = expressions.append(expression);
+                if (token.kind != ERROR) {
+                    accept(RBRACE);
+                }
+            }
+            // clean up remaining expression tokens if error
+            while (token.pos < endPos && token.kind != DEFAULT) {
+                nextToken();
+            }
+            S.setPrevToken(stringToken);
+        }
+        JCExpression t = toP(F.at(pos).StringTemplate(processor, fragments, expressions));
+        setMode(oldmode);
+        return t;
+    }
+
     JCExpression literal(Name prefix) {
         return literal(prefix, token.pos);
     }
@@ -1279,6 +1332,14 @@ public class JavacParser implements Parser {
                 t = literal(names.empty);
             } else return illegal();
             break;
+         case STRINGFRAGMENT:
+             if (typeArgs == null && isMode(EXPR)) {
+                 selectExprMode();
+                 t = stringTemplate(null);
+             } else {
+                 return illegal();
+             }
+             break;
         case NEW:
             if (typeArgs != null) return illegal();
             if (isMode(EXPR)) {
@@ -1409,6 +1470,12 @@ public class JavacParser implements Parser {
                                 t = innerCreator(pos1, typeArgs, t);
                                 typeArgs = null;
                                 break loop;
+                            case STRINGFRAGMENT:
+                            case STRINGLITERAL:
+                                if (typeArgs != null) return illegal();
+                                t = stringTemplate(t);
+                                typeArgs = null;
+                                break loop;
                             }
                         }
 
@@ -1631,6 +1698,12 @@ public class JavacParser implements Parser {
                     if (token.kind == LT) typeArgs = typeArguments(false);
                     t = innerCreator(pos2, typeArgs, t);
                     typeArgs = null;
+                } else if (token.kind == TokenKind.STRINGFRAGMENT ||
+                           token.kind == TokenKind.STRINGLITERAL) {
+                    if (typeArgs != null) {
+                        return illegal();
+                    }
+                    t = stringTemplate(t);
                 } else {
                     List<JCAnnotation> tyannos = null;
                     if (isMode(TYPE) && token.kind == MONKEYS_AT) {
@@ -1790,6 +1863,7 @@ public class JavacParser implements Parser {
                         case LPAREN: case THIS: case SUPER:
                         case INTLITERAL: case LONGLITERAL: case FLOATLITERAL:
                         case DOUBLELITERAL: case CHARLITERAL: case STRINGLITERAL:
+                        case STRINGFRAGMENT:
                         case TRUE: case FALSE: case NULL:
                         case NEW: case IDENTIFIER: case ASSERT: case ENUM: case UNDERSCORE:
                         case SWITCH:
@@ -2707,6 +2781,7 @@ public class JavacParser implements Parser {
                 boolean isYieldStatement;
                 switch (next.kind) {
                     case PLUS: case SUB: case STRINGLITERAL: case CHARLITERAL:
+                    case STRINGFRAGMENT:
                     case INTLITERAL: case LONGLITERAL: case FLOATLITERAL: case DOUBLELITERAL:
                     case NULL: case IDENTIFIER: case TRUE: case FALSE:
                     case NEW: case SWITCH: case THIS: case SUPER:

src/jdk.compiler/share/classes/com/sun/tools/javac/parser/Lexer.java

@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 2005, 2019, Oracle and/or its affiliates. All rights reserved.
+ * Copyright (c) 2005, 2023, Oracle and/or its affiliates. All rights reserved.
  * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
  *
  * This code is free software; you can redistribute it and/or modify it
@@ -59,6 +59,11 @@ public interface Lexer {
      */
     Token prevToken();
 
+    /**
+     * Sets the previous token.
+     */
+    void setPrevToken(Token prevToken);
+
     /**
      * Splits the current token in two and return the first (split) token.
      * For instance {@literal '<<<'} is split into two tokens

src/jdk.compiler/share/classes/com/sun/tools/javac/parser/Scanner.java

@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 1999, 2013, Oracle and/or its affiliates. All rights reserved.
+ * Copyright (c) 1999, 2023, Oracle and/or its affiliates. All rights reserved.
  * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
  *
  * This code is free software; you can redistribute it and/or modify it
@@ -30,8 +30,6 @@ import java.util.List;
 import java.util.ArrayList;
 
 import com.sun.tools.javac.util.Position.LineMap;
-import com.sun.tools.javac.parser.JavaTokenizer.*;
-
 import static com.sun.tools.javac.parser.Tokens.*;
 
 /** The lexical analyzer maps an input stream consisting of
@@ -44,7 +42,7 @@ import static com.sun.tools.javac.parser.Tokens.*;
  */
 public class Scanner implements Lexer {
 
-    private Tokens tokens;
+    private final Tokens tokens;
 
     /** The token, set by nextToken().
      */
@@ -56,9 +54,9 @@ public class Scanner implements Lexer {
 
     /** Buffer of saved tokens (used during lookahead)
      */
-    private List<Token> savedTokens = new ArrayList<>();
+    private final List<Token> savedTokens = new ArrayList<>();
 
-    private JavaTokenizer tokenizer;
+    private final JavaTokenizer tokenizer;
 
     /**
      * Create a scanner from the input array.  This method might
@@ -98,7 +96,7 @@ public class Scanner implements Lexer {
     }
     //where
         private void ensureLookahead(int lookahead) {
-            for (int i = savedTokens.size() ; i < lookahead ; i ++) {
+            for (int i = savedTokens.size() ; i < lookahead ; i++) {
                 savedTokens.add(tokenizer.readToken());
             }
         }
@@ -107,6 +105,10 @@ public class Scanner implements Lexer {
         return prevToken;
     }
 
+    public void setPrevToken(Token prevToken) {
+        this.prevToken = prevToken;
+    }
+
     public void nextToken() {
         prevToken = token;
         if (!savedTokens.isEmpty()) {

src/jdk.compiler/share/classes/com/sun/tools/javac/parser/Tokens.java

@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 1999, 2021, Oracle and/or its affiliates. All rights reserved.
+ * Copyright (c) 1999, 2023, Oracle and/or its affiliates. All rights reserved.
  * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
  *
  * This code is free software; you can redistribute it and/or modify it
@@ -152,6 +152,7 @@ public class Tokens {
         DOUBLELITERAL(Tag.NUMERIC),
         CHARLITERAL(Tag.NUMERIC),
         STRINGLITERAL(Tag.STRING),
+        STRINGFRAGMENT(Tag.STRING),
         TRUE("true", Tag.NAMED),
         FALSE("false", Tag.NAMED),
         NULL("null", Tag.NAMED),

src/jdk.compiler/share/classes/com/sun/tools/javac/parser/UnicodeReader.java

@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 2011, 2020, Oracle and/or its affiliates. All rights reserved.
+ * Copyright (c) 2011, 2023, Oracle and/or its affiliates. All rights reserved.
  * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
  *
  * This code is free software; you can redistribute it and/or modify it
@@ -147,6 +147,15 @@ public class UnicodeReader {
         nextCodePoint();
     }
 
+    /**
+     * Returns the character buffer.
+     *
+     * @return character buffer.
+     */
+    protected char[] buffer() {
+        return buffer;
+    }
+
     /**
      * Returns the length of the buffer. This is length of meaningful content in buffer and
      * not the length of the buffer array.
@@ -410,6 +419,9 @@ public class UnicodeReader {
     protected boolean isOneOf(char ch1, char ch2, char ch3) {
         return is(ch1) || is(ch2) || is(ch3);
     }
+    protected boolean isOneOf(char ch1, char ch2, char ch3, char ch4) {
+        return is(ch1) || is(ch2) || is(ch3) || is(ch4);
+    }
     protected boolean isOneOf(char ch1, char ch2, char ch3, char ch4, char ch5, char ch6) {
         return is(ch1) || is(ch2) || is(ch3) || is(ch4) || is(ch5) || is(ch6);
     }

src/jdk.compiler/share/classes/com/sun/tools/javac/resources/compiler.properties

@@ -1322,6 +1322,23 @@ compiler.err.unclosed.str.lit=\
 compiler.err.unclosed.text.block=\
     unclosed text block
 
+compiler.err.string.template.is.not.well.formed=\
+    string template is not well formed
+
+compiler.err.text.block.template.is.not.well.formed=\
+    text block template is not well formed
+
+compiler.err.processor.missing.from.string.template.expression=\
+    processor missing from string template expression
+
+# 0: symbol
+compiler.err.processor.type.cannot.be.a.raw.type=\
+    processor type cannot be a raw type: {0}
+
+# 0: symbol
+compiler.err.not.a.processor.type=\
+    not a processor type: {0}
+
 # 0: string
 compiler.err.unsupported.encoding=\
     unsupported encoding: {0}
@@ -3127,6 +3144,9 @@ compiler.misc.feature.case.null=\
 compiler.misc.feature.pattern.switch=\
     patterns in switch statements
 
+compiler.misc.feature.string.templates=\
+    string templates
+
 compiler.misc.feature.unconditional.patterns.in.instanceof=\
     unconditional patterns in instanceof
 

src/jdk.compiler/share/classes/com/sun/tools/javac/tree/JCTree.java

@@ -269,6 +269,10 @@ public abstract class JCTree implements Tree, Cloneable, DiagnosticPosition {
          */
         LITERAL,
 
+        /** String template expression.
+         */
+        STRING_TEMPLATE,
+
         /** Basic type identifiers, of type TypeIdent.
          */
         TYPEIDENT,
@@ -2499,6 +2503,58 @@ public abstract class JCTree implements Tree, Cloneable, DiagnosticPosition {
 
     }
 
+    /**
+     * String template expression.
+     */
+    public static class JCStringTemplate extends JCExpression implements StringTemplateTree {
+        public JCExpression processor;
+        public List<String> fragments;
+        public List<JCExpression> expressions;
+
+        protected JCStringTemplate(JCExpression processor,
+                                   List<String> fragments,
+                                   List<JCExpression> expressions) {
+            this.processor = processor;
+            this.fragments = fragments;
+            this.expressions = expressions;
+        }
+
+        @Override
+        public ExpressionTree getProcessor() {
+            return processor;
+        }
+
+        @Override
+        public List<String> getFragments() {
+            return fragments;
+        }
+
+        @Override
+        public List<? extends ExpressionTree> getExpressions() {
+            return expressions;
+        }
+
+        @Override @DefinedBy(Api.COMPILER_TREE)
+        public Kind getKind() {
+            return Kind.TEMPLATE;
+        }
+
+        @Override @DefinedBy(Api.COMPILER_TREE)
+        public Tag getTag() {
+            return STRING_TEMPLATE;
+        }
+
+        @Override @DefinedBy(Api.COMPILER_TREE)
+        public void accept(Visitor v) {
+            v.visitStringTemplate(this);
+        }
+
+        @Override @DefinedBy(Api.COMPILER_TREE)
+        public <R, D> R accept(TreeVisitor<R, D> v, D d) {
+            return v.visitStringTemplate(this, d);
+        }
+    }
+
     /**
      * An array selection
      */
@@ -3478,6 +3534,9 @@ public abstract class JCTree implements Tree, Cloneable, DiagnosticPosition {
         JCFieldAccess Select(JCExpression selected, Name selector);
         JCIdent Ident(Name idname);
         JCLiteral Literal(TypeTag tag, Object value);
+        JCStringTemplate StringTemplate(JCExpression processor,
+                                        List<String> fragments,
+                                        List<JCExpression> expressions);
         JCPrimitiveTypeTree TypeIdent(TypeTag typetag);
         JCArrayTypeTree TypeArray(JCExpression elemtype);
         JCTypeApply TypeApply(JCExpression clazz, List<JCExpression> arguments);
@@ -3549,6 +3608,7 @@ public abstract class JCTree implements Tree, Cloneable, DiagnosticPosition {
         public void visitReference(JCMemberReference that)   { visitTree(that); }
         public void visitIdent(JCIdent that)                 { visitTree(that); }
         public void visitLiteral(JCLiteral that)             { visitTree(that); }
+        public void visitStringTemplate(JCStringTemplate that) { visitTree(that); }
         public void visitTypeIdent(JCPrimitiveTypeTree that) { visitTree(that); }
         public void visitTypeArray(JCArrayTypeTree that)     { visitTree(that); }
         public void visitTypeApply(JCTypeApply that)         { visitTree(that); }

src/jdk.compiler/share/classes/com/sun/tools/javac/tree/Pretty.java

@@ -26,6 +26,7 @@
 package com.sun.tools.javac.tree;
 
 import java.io.*;
+import java.util.stream.Collectors;
 
 import com.sun.source.tree.MemberReferenceTree.ReferenceMode;
 import com.sun.source.tree.ModuleTree.ModuleKind;
@@ -1474,6 +1475,23 @@ public class Pretty extends JCTree.Visitor {
         }
     }
 
+    public void visitStringTemplate(JCStringTemplate tree) {
+        try {
+            JCExpression processor = tree.processor;
+            print("[");
+            if (processor != null) {
+                printExpr(processor);
+            }
+            print("]");
+            print("\"" + tree.fragments.stream().collect(Collectors.joining("\\{}")) + "\"");
+            print("(");
+            printExprs(tree.expressions);
+            print(")");
+        } catch (IOException e) {
+            throw new UncheckedIOException(e);
+        }
+    }
+
     public void visitTypeIdent(JCPrimitiveTypeTree tree) {
         try {
             switch(tree.typetag) {

src/jdk.compiler/share/classes/com/sun/tools/javac/tree/TreeCopier.java

@@ -282,6 +282,14 @@ public class TreeCopier<P> implements TreeVisitor<JCTree,P> {
         return M.at(t.pos).Literal(t.typetag, t.value);
     }
 
+    @DefinedBy(Api.COMPILER_TREE)
+    public JCTree visitStringTemplate(StringTemplateTree node, P p) {
+        JCStringTemplate t = (JCStringTemplate) node;
+        JCExpression processor = copy(t.processor, p);
+        List<JCExpression> expressions = copy(t.expressions, p);
+        return M.at(t.pos).StringTemplate(processor, t.fragments, expressions);
+    }
+
     @DefinedBy(Api.COMPILER_TREE)
     public JCTree visitMethod(MethodTree node, P p) {
         JCMethodDecl t  = (JCMethodDecl) node;

src/jdk.compiler/share/classes/com/sun/tools/javac/tree/TreeInfo.java

@@ -330,6 +330,7 @@ public class TreeInfo {
             case PLUS_ASG: case MINUS_ASG:
             case MUL_ASG: case DIV_ASG: case MOD_ASG:
             case APPLY: case NEWCLASS:
+            case STRING_TEMPLATE:
             case ERRONEOUS:
                 return true;
             default:
@@ -545,6 +546,14 @@ public class TreeInfo {
                 JCBindingPattern node = (JCBindingPattern)tree;
                 return getStartPos(node.var);
             }
+            case STRING_TEMPLATE: {
+                JCStringTemplate node = (JCStringTemplate) tree;
+                if (node.processor == null) {
+                    return node.pos;
+                } else {
+                    return getStartPos(node.processor);
+                }
+            }
             case ERRONEOUS: {
                 JCErroneous node = (JCErroneous)tree;
                 if (node.errs != null && node.errs.nonEmpty()) {
@@ -973,6 +982,8 @@ public class TreeInfo {
             return symbol(((JCAnnotatedType) tree).underlyingType);
         case REFERENCE:
             return ((JCMemberReference) tree).sym;
+        case CLASSDEF:
+            return ((JCClassDecl) tree).sym;
         default:
             return null;
         }

src/jdk.compiler/share/classes/com/sun/tools/javac/tree/TreeMaker.java

@@ -550,6 +550,14 @@ public class TreeMaker implements JCTree.Factory {
         return tree;
     }
 
+    public JCStringTemplate StringTemplate(JCExpression processor,
+                                           List<String> fragments,
+                                           List<JCExpression> expressions) {
+        JCStringTemplate tree = new JCStringTemplate(processor, fragments, expressions);
+        tree.pos = pos;
+        return tree;
+    }
+
     public JCPrimitiveTypeTree TypeIdent(TypeTag typetag) {
         JCPrimitiveTypeTree tree = new JCPrimitiveTypeTree(typetag);
         tree.pos = pos;

src/jdk.compiler/share/classes/com/sun/tools/javac/tree/TreeScanner.java

@@ -353,6 +353,11 @@ public class TreeScanner extends Visitor {
     public void visitLiteral(JCLiteral tree) {
     }
 
+    public void visitStringTemplate(JCStringTemplate tree) {
+        scan(tree.processor);
+        scan(tree.expressions);
+    }
+
     public void visitTypeIdent(JCPrimitiveTypeTree tree) {
     }
 

src/jdk.compiler/share/classes/com/sun/tools/javac/tree/TreeTranslator.java

@@ -411,6 +411,13 @@ public class TreeTranslator extends JCTree.Visitor {
         result = tree;
     }
 
+    public void visitStringTemplate(JCStringTemplate tree) {
+        tree.processor = translate(tree.processor);
+        tree.expressions = translate(tree.expressions);
+
+        result = tree;
+    }
+
     public void visitTypeIdent(JCPrimitiveTypeTree tree) {
         result = tree;
     }

src/jdk.compiler/share/classes/com/sun/tools/javac/util/Names.java

@@ -222,6 +222,14 @@ public class Names {
     public final Name typeSwitch;
     public final Name enumSwitch;
 
+    // templated string
+    public final Name process;
+    public final Name STR;
+    public final Name RAW;
+    public final Name newStringTemplate;
+    public final Name newLargeStringTemplate;
+    public final Name processStringTemplate;
+
     public final Name.Table table;
 
     @SuppressWarnings("this-escape")
@@ -396,6 +404,14 @@ public class Names {
         permits = fromString("permits");
         sealed = fromString("sealed");
 
+        // templated string
+        process = fromString("process");
+        STR = fromString("STR");
+        RAW = fromString("RAW");
+        newStringTemplate = fromString("newStringTemplate");
+        newLargeStringTemplate = fromString("newLargeStringTemplate");
+        processStringTemplate = fromString("processStringTemplate");
+
         // pattern switches
         typeSwitch = fromString("typeSwitch");
         enumSwitch = fromString("enumSwitch");

src/jdk.jshell/share/classes/jdk/jshell/CompletenessAnalyzer.java

@@ -272,6 +272,7 @@ class CompletenessAnalyzer {
         DOUBLELITERAL(TokenKind.DOUBLELITERAL, XEXPR1|XTERM),  //
         CHARLITERAL(TokenKind.CHARLITERAL, XEXPR1|XTERM),  //
         STRINGLITERAL(TokenKind.STRINGLITERAL, XEXPR1|XTERM),  //
+        STRINGFRAGMENT(TokenKind.STRINGFRAGMENT, XEXPR1|XTERM),
         TRUE(TokenKind.TRUE, XEXPR1|XTERM),  //  true
         FALSE(TokenKind.FALSE, XEXPR1|XTERM),  //  false
         NULL(TokenKind.NULL, XEXPR1|XTERM),  //  null
@@ -479,8 +480,16 @@ class CompletenessAnalyzer {
 
         private Token advance() {
             Token prev = current;
-            scanner.nextToken();
+            if (current != null && current.kind == TokenKind.STRINGFRAGMENT) {
-            current = scanner.token();
+                int endPos = current.endPos;
+                do {
+                    scanner.nextToken();
+                    current = scanner.token();
+                } while (current != null && current.endPos <= endPos && current.kind != TokenKind.EOF);
+            } else {
+                scanner.nextToken();
+                current = scanner.token();
+            }
             return prev;
         }
 

test/jdk/java/lang/String/concat/MakeConcatWithTemplate.java

@@ -0,0 +1,139 @@
+/*
+ * Copyright (c) 2023, Oracle and/or its affiliates. All rights reserved.
+ * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
+ *
+ * This code is free software; you can redistribute it and/or modify it
+ * under the terms of the GNU General Public License version 2 only, as
+ * published by the Free Software Foundation.
+ *
+ * This code is distributed in the hope that it will be useful, but WITHOUT
+ * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
+ * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
+ * version 2 for more details (a copy is included in the LICENSE file that
+ * accompanied this code).
+ *
+ * You should have received a copy of the GNU General Public License version
+ * 2 along with this work; if not, write to the Free Software Foundation,
+ * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
+ *
+ * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
+ * or visit www.oracle.com if you need additional information or have any
+ * questions.
+ */
+
+import java.lang.invoke.MethodHandle;
+import java.lang.invoke.MethodHandles;
+import java.lang.invoke.StringConcatFactory;
+import java.util.ArrayList;
+import java.util.Arrays;
+import java.util.List;
+
+/**
+ * @test
+ * @summary Test StringConcatFactory.makeConcatWithTemplate... methods.
+ * @enablePreview true
+ */
+
+public class MakeConcatWithTemplate {
+    public static void main(String... args) {
+        makeConcatWithTemplate();
+        makeConcatWithTemplateCluster();
+        makeConcatWithTemplateGetters();
+    }
+
+    static List<String> fragments(int n) {
+        String[] array = new String[n];
+        Arrays.fill(array, "abc");
+        return Arrays.asList(array);
+    }
+
+    static List<Class<?>> types(int n) {
+        Class<?>[] array = new Class<?>[n];
+        Arrays.fill(array, int.class);
+        return Arrays.asList(array);
+    }
+
+    static List<Integer> values(int n) {
+        Integer[] array = new Integer[n];
+        Arrays.fill(array, 123);
+        return Arrays.asList(array);
+    }
+
+    static List<MethodHandle> getters(int n) {
+        MethodHandle[] array = new MethodHandle[n];
+        MethodHandle m = MethodHandles.dropArguments(MethodHandles.constant(int.class, 123), 0, Object.class);
+        Arrays.fill(array, m);
+        return Arrays.asList(array);
+    }
+
+    static void makeConcatWithTemplate() {
+        try {
+            int n = StringConcatFactory.MAX_INDY_CONCAT_ARG_SLOTS - 1;
+            MethodHandle m = StringConcatFactory.makeConcatWithTemplate(fragments(n + 1), types(n));
+            m.invokeWithArguments(values(n));
+        } catch (Throwable e) {
+            throw new RuntimeException(e);
+        }
+
+        try {
+            int n = StringConcatFactory.MAX_INDY_CONCAT_ARG_SLOTS;
+            MethodHandle m = StringConcatFactory.makeConcatWithTemplate(fragments(n + 1), types(n));
+            m.invokeWithArguments(values(n));
+        } catch (Throwable e) {
+            throw new RuntimeException(e);
+        }
+
+        boolean threw = false;
+        try {
+            int n = StringConcatFactory.MAX_INDY_CONCAT_ARG_SLOTS + 1;
+            MethodHandle m = StringConcatFactory.makeConcatWithTemplate(fragments(n + 1), types(n));
+            m.invokeWithArguments(values(n));
+        } catch (Throwable e) {
+            threw = true;
+        }
+
+        if (!threw) {
+            throw new RuntimeException("Exception expected - makeConcatWithTemplate");
+        }
+    }
+
+    static void makeConcatWithTemplateCluster() {
+        int n = StringConcatFactory.MAX_INDY_CONCAT_ARG_SLOTS;
+        int c = 3;
+        try {
+            List<MethodHandle> ms = StringConcatFactory.makeConcatWithTemplateCluster(fragments(c * n + 1), types(c * n), n);
+            MethodHandle m0 = ms.get(0);
+            MethodHandle m1 = ms.get(1);
+            MethodHandle m2 = ms.get(2);
+            MethodHandle m3 = ms.get(3);
+
+            String s = (String)m0.invokeWithArguments(values(n));
+            List<Object> args = new ArrayList<>();
+            args.add(s);
+            args.addAll(values(n - 1)); // one less for carry over string
+            s = (String)m1.invokeWithArguments(args);
+            args.clear();
+            args.add(s);
+            args.addAll(values(n - 1)); // one less for carry over string
+            s = (String)m2.invokeWithArguments(args);
+            args.clear();
+            args.add(s);
+            args.addAll(values(2)); // two remaining carry overs
+            s = (String)m3.invokeWithArguments(args);
+        } catch (Throwable e) {
+            throw new RuntimeException(e);
+        }
+    }
+
+    static void makeConcatWithTemplateGetters() {
+        int n = StringConcatFactory.MAX_INDY_CONCAT_ARG_SLOTS;
+        int c = 3;
+        try {
+            MethodHandle m = StringConcatFactory.makeConcatWithTemplateGetters(fragments(c * n + 1), getters(c * n), n);
+            String s = (String)m.invoke(null);
+        } catch (Throwable e) {
+            throw new RuntimeException(e);
+        }
+    }
+
+}

test/jdk/java/lang/runtime/CarriersTest.java

@@ -0,0 +1,166 @@
+/*
+ * Copyright (c) 2023, Oracle and/or its affiliates. All rights reserved.
+ * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
+ *
+ * This code is free software; you can redistribute it and/or modify it
+ * under the terms of the GNU General Public License version 2 only, as
+ * published by the Free Software Foundation.
+ *
+ * This code is distributed in the hope that it will be useful, but WITHOUT
+ * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
+ * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
+ * version 2 for more details (a copy is included in the LICENSE file that
+ * accompanied this code).
+ *
+ * You should have received a copy of the GNU General Public License version
+ * 2 along with this work; if not, write to the Free Software Foundation,
+ * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
+ *
+ * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
+ * or visit www.oracle.com if you need additional information or have any
+ * questions.
+ */
+
+/*
+ * @test
+ * @summary Test features provided by the Carriers class.
+ * @modules java.base/java.lang.runtime
+ * @enablePreview true
+ * @compile --patch-module java.base=${test.src} CarriersTest.java
+ * @run main/othervm --patch-module java.base=${test.class.path} java.lang.runtime.CarriersTest
+ */
+
+package java.lang.runtime;
+
+import java.lang.invoke.MethodHandle;
+import java.lang.invoke.MethodType;
+import java.util.Arrays;
+import java.util.List;
+
+public class CarriersTest {
+    public static void main(String[] args) throws Throwable {
+        primitivesTest();
+        primitivesTestLarge();
+        limitsTest();
+    }
+
+    static void assertTrue(boolean test, String message) {
+        if (!test) {
+            throw new RuntimeException(message);
+        }
+    }
+
+    static final int MAX_COMPONENTS = 254;
+
+    static void primitivesTest() throws Throwable {
+        MethodType methodType =
+                MethodType.methodType(Object.class, byte.class, short.class,
+                        char.class, int.class, long.class,
+                        float.class, double.class,
+                        boolean.class, String.class);
+        MethodHandle constructor = Carriers.initializingConstructor(methodType);
+        Object object = (Object)constructor.invokeExact((byte)0xFF, (short)0xFFFF,
+                'C', 0xFFFFFFFF, 0xFFFFFFFFFFFFFFFFL,
+                1.0f / 3.0f, 1.0 / 3.0,
+                true, "abcde");
+        List<MethodHandle> components = Carriers.components(methodType);
+        assertTrue((byte)components.get(0).invokeExact(object) == (byte)0xFF,
+                "primitive byte test failure");
+        assertTrue((short)components.get(1).invokeExact(object) == (short)0xFFFF,
+                "primitive short test failure");
+        assertTrue((char)components.get(2).invokeExact(object) == 'C',
+                "primitive char test failure");
+        assertTrue((int)components.get(3).invokeExact(object) == 0xFFFFFFFF,
+                "primitive int test failure");
+        assertTrue((long)components.get(4).invokeExact(object) == 0xFFFFFFFFFFFFFFFFL,
+                "primitive long test failure");
+        assertTrue((float)components.get(5).invokeExact(object) == 1.0f / 3.0f,
+                "primitive float test failure");
+        assertTrue((double)components.get(6).invokeExact(object) == 1.0 / 3.0,
+                "primitive double test failure");
+        assertTrue((boolean)components.get(7).invokeExact(object),
+                "primitive boolean test failure");
+        assertTrue("abcde".equals((String)components.get(8).invokeExact(object)),
+                "primitive String test failure");
+    }
+
+    static void primitivesTestLarge() throws Throwable {
+        MethodType methodType =
+                MethodType.methodType(Object.class, byte.class, short.class,
+                        char.class, int.class, long.class,
+                        float.class, double.class,
+                        boolean.class, String.class,
+                        Object.class, Object.class,Object.class,Object.class,
+                        Object.class, Object.class,Object.class,Object.class,
+                        Object.class, Object.class,Object.class,Object.class,
+                        Object.class, Object.class,Object.class,Object.class,
+                        Object.class, Object.class,Object.class,Object.class,
+                        Object.class, Object.class,Object.class,Object.class,
+                        Object.class, Object.class,Object.class,Object.class
+                );
+        MethodHandle constructor = Carriers.initializingConstructor(methodType);
+        Object object = (Object)constructor.invokeExact((byte)0xFF, (short)0xFFFF,
+                'C', 0xFFFFFFFF, 0xFFFFFFFFFFFFFFFFL,
+                1.0f / 3.0f, 1.0 / 3.0,
+                true, "abcde",
+                (Object)null, (Object)null, (Object)null, (Object)null,
+                (Object)null, (Object)null, (Object)null, (Object)null,
+                (Object)null, (Object)null, (Object)null, (Object)null,
+                (Object)null, (Object)null, (Object)null, (Object)null,
+                (Object)null, (Object)null, (Object)null, (Object)null,
+                (Object)null, (Object)null, (Object)null, (Object)null,
+                (Object)null, (Object)null, (Object)null, (Object)null
+        );
+        List<MethodHandle> components = Carriers.components(methodType);
+        assertTrue((byte)components.get(0).invokeExact(object) == (byte)0xFF,
+                "large primitive byte test failure");
+        assertTrue((short)components.get(1).invokeExact(object) == (short)0xFFFF,
+                "large primitive short test failure");
+        assertTrue((char)components.get(2).invokeExact(object) == 'C',
+                "large primitive char test failure");
+        assertTrue((int)components.get(3).invokeExact(object) == 0xFFFFFFFF,
+                "large primitive int test failure");
+        assertTrue((long)components.get(4).invokeExact(object) == 0xFFFFFFFFFFFFFFFFL,
+                "large primitive long test failure");
+        assertTrue((float)components.get(5).invokeExact(object) == 1.0f / 3.0f,
+                "large primitive float test failure");
+        assertTrue((double)components.get(6).invokeExact(object) == 1.0 / 3.0,
+                "large primitive double test failure");
+        assertTrue((boolean)components.get(7).invokeExact(object),
+                "large primitive boolean test failure");
+        assertTrue("abcde".equals((String)components.get(8).invokeExact(object)),
+                "large primitive String test failure");
+    }
+
+    static void limitsTest() {
+        boolean passed;
+
+        passed = false;
+        try {
+            Class<?>[] ptypes = new Class<?>[MAX_COMPONENTS + 1];
+            Arrays.fill(ptypes, Object.class);
+            MethodType methodType = MethodType.methodType(Object.class, ptypes);
+            MethodHandle constructor = Carriers.constructor(methodType);
+        } catch (IllegalArgumentException ex) {
+            passed = true;
+        }
+
+        if (!passed) {
+            throw new RuntimeException("failed to report too many components ");
+        }
+
+        passed = false;
+        try {
+            Class<?>[] ptypes = new Class<?>[MAX_COMPONENTS / 2 + 1];
+            Arrays.fill(ptypes, long.class);
+            MethodType methodType = MethodType.methodType(Object.class, ptypes);
+            MethodHandle constructor = Carriers.constructor(methodType);
+        } catch (IllegalArgumentException ex) {
+            passed = true;
+        }
+
+        if (!passed) {
+            throw new RuntimeException("failed to report too many components ");
+        }
+    }
+}

test/jdk/java/lang/runtime/ReferencedKeyTest.java

@@ -0,0 +1,109 @@
+/*
+ * Copyright (c) 2023, Oracle and/or its affiliates. All rights reserved.
+ * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
+ *
+ * This code is free software; you can redistribute it and/or modify it
+ * under the terms of the GNU General Public License version 2 only, as
+ * published by the Free Software Foundation.
+ *
+ * This code is distributed in the hope that it will be useful, but WITHOUT
+ * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
+ * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
+ * version 2 for more details (a copy is included in the LICENSE file that
+ * accompanied this code).
+ *
+ * You should have received a copy of the GNU General Public License version
+ * 2 along with this work; if not, write to the Free Software Foundation,
+ * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
+ *
+ * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
+ * or visit www.oracle.com if you need additional information or have any
+ * questions.
+ */
+
+/*
+ * @test
+ * @summary Test features provided by the ReferencedKeyMap class.
+ * @modules java.base/java.lang.runtime
+ * @enablePreview
+ * @compile --patch-module java.base=${test.src} ReferencedKeyTest.java
+ * @run main/othervm --patch-module java.base=${test.class.path} java.lang.runtime.ReferencedKeyTest
+ */
+
+package java.lang.runtime;
+
+import java.util.HashMap;
+import java.util.Map;
+import java.util.concurrent.ConcurrentHashMap;
+import java.util.function.Supplier;
+
+public class ReferencedKeyTest {
+    static long BASE_KEY = 10_000_000L;
+
+    public static void main(String[] args) throws Throwable {
+        mapTest(false, HashMap::new);
+        mapTest(true, HashMap::new);
+        mapTest(false, ConcurrentHashMap::new);
+        mapTest(true, ConcurrentHashMap::new);
+    }
+
+    static void assertTrue(boolean test, String message) {
+        if (!test) {
+            throw new RuntimeException(message);
+        }
+    }
+
+    static void  mapTest(boolean isSoft, Supplier<Map<ReferenceKey<Long>, String>> supplier) {
+        Map<Long, String> map = ReferencedKeyMap.create(isSoft, supplier);
+        populate(map);
+        collect();
+        // assertTrue(map.isEmpty() || isSoft, "Weak not collecting");
+        populate(map);
+        methods(map);
+    }
+
+    static void methods(Map<Long, String> map) {
+        assertTrue(map.size() == 26, "missing key");
+        assertTrue(map.containsKey(BASE_KEY + 'a' -'a'), "missing key");
+        assertTrue(map.get(BASE_KEY + 'b' -'a').equals("b"), "wrong key");
+        assertTrue(map.containsValue("c"), "missing value");
+        map.remove(BASE_KEY + 'd' -'a');
+        assertTrue(map.get(BASE_KEY + 'd' -'a') == null, "not removed");
+        map.putAll(Map.of(1L, "A", 2L, "B"));
+        assertTrue(map.get(2L).equals("B"), "collection not added");
+        assertTrue(map.keySet().contains(1L), "key missing");
+        assertTrue(map.values().contains("A"), "key missing");
+        assertTrue(map.entrySet().contains(Map.entry(1L, "A")), "key missing");
+        map.putIfAbsent(3L, "C");
+        assertTrue(map.get(3L).equals("C"), "key missing");
+        map.putIfAbsent(2L, "D");
+        assertTrue(map.get(2L).equals("B"), "key replaced");
+        map.remove(3L);
+        assertTrue(map.get(3L) == null, "key not removed");
+        map.replace(2L, "D");
+        assertTrue(map.get(2L).equals("D"), "key not replaced");
+        map.replace(2L, "B", "E");
+        assertTrue(map.get(2L).equals("D"), "key replaced");
+    }
+
+    static void collect() {
+        System.gc();
+        sleep();
+    }
+
+    static void sleep() {
+        try {
+            Thread.sleep(100L);
+        } catch (InterruptedException e) {
+            throw new RuntimeException(e);
+        }
+    }
+
+    static void populate(Map<Long, String> map) {
+        for (int i = 0; i < 26; i++) {
+            Long key = BASE_KEY + i;
+            String value = String.valueOf((char) ('a' + i));
+            map.put(key, value);
+        }
+    }
+}

test/jdk/java/lang/template/Basic.java

@@ -0,0 +1,504 @@
+/*
+ * Copyright (c) 2023, Oracle and/or its affiliates. All rights reserved.
+ * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
+ *
+ * This code is free software; you can redistribute it and/or modify it
+ * under the terms of the GNU General Public License version 2 only, as
+ * published by the Free Software Foundation.
+ *
+ * This code is distributed in the hope that it will be useful, but WITHOUT
+ * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
+ * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
+ * version 2 for more details (a copy is included in the LICENSE file that
+ * accompanied this code).
+ *
+ * You should have received a copy of the GNU General Public License version
+ * 2 along with this work; if not, write to the Free Software Foundation,
+ * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
+ *
+ * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
+ * or visit www.oracle.com if you need additional information or have any
+ * questions.
+ */
+
+/*
+ * @test
+ * @bug 0000000
+ * @summary Exercise runtime handing of templated strings.
+ * @enablePreview true
+ */
+
+import java.lang.StringTemplate.*;
+import java.util.*;
+import java.util.concurrent.*;
+import java.util.function.*;
+
+import static java.lang.StringTemplate.RAW;
+
+public class Basic {
+    public static void main(String... arg) {
+        equalsHashCode();
+        concatenationTests();
+        componentTests();
+        limitsTests();
+        processorTests();
+        stringTemplateCoverage();
+        simpleProcessorCoverage();
+    }
+
+    static void ASSERT(String a, String b) {
+        if (!Objects.equals(a, b)) {
+            System.out.println(a);
+            System.out.println(b);
+            throw new RuntimeException("Test failed");
+        }
+    }
+
+    static void ASSERT(Object a, Object b) {
+        if (!Objects.deepEquals(a, b)) {
+            System.out.println(a);
+            System.out.println(b);
+            throw new RuntimeException("Test failed");
+        }
+    }
+
+    /*
+     * equals and hashCode tests.
+     */
+    static void equalsHashCode() {
+        int x = 10;
+        int y = 20;
+        int a = 10;
+        int b = 20;
+
+        StringTemplate st0 = RAW."\{x} + \{y} = \{x + y}";
+        StringTemplate st1 = RAW."\{a} + \{b} = \{a + b}";
+        StringTemplate st2 = RAW."\{x} + \{y} = \{x + y}!";
+        x++;
+        StringTemplate st3 = RAW."\{x} + \{y} = \{x + y}";
+
+        if (!st0.equals(st1)) throw new RuntimeException("st0 != st1");
+        if (st0.equals(st2)) throw new RuntimeException("st0 == st2");
+        if (st0.equals(st3)) throw new RuntimeException("st0 == st3");
+
+        if (st0.hashCode() != st1.hashCode()) throw new RuntimeException("st0.hashCode() != st1.hashCode()");
+    }
+
+    /*
+     * Concatenation tests.
+     */
+    static void concatenationTests() {
+        int x = 10;
+        int y = 20;
+
+        ASSERT(STR."\{x} \{y}", x + " " + y);
+        ASSERT(STR."\{x + y}", "" + (x + y));
+        ASSERT(STR.process(RAW."\{x} \{y}"), x + " " + y);
+        ASSERT(STR.process(RAW."\{x + y}"), "" + (x + y));
+        ASSERT((RAW."\{x} \{y}").process(STR), x + " " + y);
+        ASSERT((RAW."\{x + y}").process(STR), "" + (x + y));
+    }
+
+    /*
+     * Component tests.
+     */
+    static void componentTests() {
+        int x = 10;
+        int y = 20;
+
+        StringTemplate st = RAW."\{x} + \{y} = \{x + y}";
+        ASSERT(st.values(), List.of(x, y, x + y));
+        ASSERT(st.fragments(), List.of("", " + ", " = ", ""));
+        ASSERT(st.interpolate(), x + " + " + y + " = " + (x + y));
+    }
+
+    /*
+     * Limits tests.
+     */
+    static void limitsTests() {
+        int x = 9;
+
+        StringTemplate ts250 = RAW."""
+             \{x}\{x}\{x}\{x}\{x}\{x}\{x}\{x}\{x}\{x} \{x}\{x}\{x}\{x}\{x}\{x}\{x}\{x}\{x}\{x}
+             \{x}\{x}\{x}\{x}\{x}\{x}\{x}\{x}\{x}\{x} \{x}\{x}\{x}\{x}\{x}\{x}\{x}\{x}\{x}\{x}
+             \{x}\{x}\{x}\{x}\{x}\{x}\{x}\{x}\{x}\{x} \{x}\{x}\{x}\{x}\{x}\{x}\{x}\{x}\{x}\{x}
+             \{x}\{x}\{x}\{x}\{x}\{x}\{x}\{x}\{x}\{x} \{x}\{x}\{x}\{x}\{x}\{x}\{x}\{x}\{x}\{x}
+             \{x}\{x}\{x}\{x}\{x}\{x}\{x}\{x}\{x}\{x} \{x}\{x}\{x}\{x}\{x}\{x}\{x}\{x}\{x}\{x}
+
+             \{x}\{x}\{x}\{x}\{x}\{x}\{x}\{x}\{x}\{x} \{x}\{x}\{x}\{x}\{x}\{x}\{x}\{x}\{x}\{x}
+             \{x}\{x}\{x}\{x}\{x}\{x}\{x}\{x}\{x}\{x} \{x}\{x}\{x}\{x}\{x}\{x}\{x}\{x}\{x}\{x}
+             \{x}\{x}\{x}\{x}\{x}\{x}\{x}\{x}\{x}\{x} \{x}\{x}\{x}\{x}\{x}\{x}\{x}\{x}\{x}\{x}
+             \{x}\{x}\{x}\{x}\{x}\{x}\{x}\{x}\{x}\{x} \{x}\{x}\{x}\{x}\{x}\{x}\{x}\{x}\{x}\{x}
+             \{x}\{x}\{x}\{x}\{x}\{x}\{x}\{x}\{x}\{x} \{x}\{x}\{x}\{x}\{x}\{x}\{x}\{x}\{x}\{x}
+
+             \{x}\{x}\{x}\{x}\{x}\{x}\{x}\{x}\{x}\{x} \{x}\{x}\{x}\{x}\{x}\{x}\{x}\{x}\{x}\{x}
+             \{x}\{x}\{x}\{x}\{x}\{x}\{x}\{x}\{x}\{x} \{x}\{x}\{x}\{x}\{x}\{x}\{x}\{x}\{x}\{x}
+             \{x}\{x}\{x}\{x}\{x}\{x}\{x}\{x}\{x}\{x}
+             """;
+        ASSERT(ts250.values().size(), 250);
+        ASSERT(ts250.interpolate(), """
+               9999999999 9999999999
+               9999999999 9999999999
+               9999999999 9999999999
+               9999999999 9999999999
+               9999999999 9999999999
+
+               9999999999 9999999999
+               9999999999 9999999999
+               9999999999 9999999999
+               9999999999 9999999999
+               9999999999 9999999999
+
+               9999999999 9999999999
+               9999999999 9999999999
+               9999999999
+               """);
+
+        StringTemplate ts251 = RAW."""
+             \{x}\{x}\{x}\{x}\{x}\{x}\{x}\{x}\{x}\{x} \{x}\{x}\{x}\{x}\{x}\{x}\{x}\{x}\{x}\{x}
+             \{x}\{x}\{x}\{x}\{x}\{x}\{x}\{x}\{x}\{x} \{x}\{x}\{x}\{x}\{x}\{x}\{x}\{x}\{x}\{x}
+             \{x}\{x}\{x}\{x}\{x}\{x}\{x}\{x}\{x}\{x} \{x}\{x}\{x}\{x}\{x}\{x}\{x}\{x}\{x}\{x}
+             \{x}\{x}\{x}\{x}\{x}\{x}\{x}\{x}\{x}\{x} \{x}\{x}\{x}\{x}\{x}\{x}\{x}\{x}\{x}\{x}
+             \{x}\{x}\{x}\{x}\{x}\{x}\{x}\{x}\{x}\{x} \{x}\{x}\{x}\{x}\{x}\{x}\{x}\{x}\{x}\{x}
+
+             \{x}\{x}\{x}\{x}\{x}\{x}\{x}\{x}\{x}\{x} \{x}\{x}\{x}\{x}\{x}\{x}\{x}\{x}\{x}\{x}
+             \{x}\{x}\{x}\{x}\{x}\{x}\{x}\{x}\{x}\{x} \{x}\{x}\{x}\{x}\{x}\{x}\{x}\{x}\{x}\{x}
+             \{x}\{x}\{x}\{x}\{x}\{x}\{x}\{x}\{x}\{x} \{x}\{x}\{x}\{x}\{x}\{x}\{x}\{x}\{x}\{x}
+             \{x}\{x}\{x}\{x}\{x}\{x}\{x}\{x}\{x}\{x} \{x}\{x}\{x}\{x}\{x}\{x}\{x}\{x}\{x}\{x}
+             \{x}\{x}\{x}\{x}\{x}\{x}\{x}\{x}\{x}\{x} \{x}\{x}\{x}\{x}\{x}\{x}\{x}\{x}\{x}\{x}
+
+             \{x}\{x}\{x}\{x}\{x}\{x}\{x}\{x}\{x}\{x} \{x}\{x}\{x}\{x}\{x}\{x}\{x}\{x}\{x}\{x}
+             \{x}\{x}\{x}\{x}\{x}\{x}\{x}\{x}\{x}\{x} \{x}\{x}\{x}\{x}\{x}\{x}\{x}\{x}\{x}\{x}
+             \{x}\{x}\{x}\{x}\{x}\{x}\{x}\{x}\{x}\{x} \{x}
+             """;
+        ASSERT(ts251.values().size(), 251);
+        ASSERT(ts251.interpolate(), """
+               9999999999 9999999999
+               9999999999 9999999999
+               9999999999 9999999999
+               9999999999 9999999999
+               9999999999 9999999999
+
+               9999999999 9999999999
+               9999999999 9999999999
+               9999999999 9999999999
+               9999999999 9999999999
+               9999999999 9999999999
+
+               9999999999 9999999999
+               9999999999 9999999999
+               9999999999 9
+               """);
+
+        StringTemplate ts252 = RAW."""
+             \{x}\{x}\{x}\{x}\{x}\{x}\{x}\{x}\{x}\{x} \{x}\{x}\{x}\{x}\{x}\{x}\{x}\{x}\{x}\{x}
+             \{x}\{x}\{x}\{x}\{x}\{x}\{x}\{x}\{x}\{x} \{x}\{x}\{x}\{x}\{x}\{x}\{x}\{x}\{x}\{x}
+             \{x}\{x}\{x}\{x}\{x}\{x}\{x}\{x}\{x}\{x} \{x}\{x}\{x}\{x}\{x}\{x}\{x}\{x}\{x}\{x}
+             \{x}\{x}\{x}\{x}\{x}\{x}\{x}\{x}\{x}\{x} \{x}\{x}\{x}\{x}\{x}\{x}\{x}\{x}\{x}\{x}
+             \{x}\{x}\{x}\{x}\{x}\{x}\{x}\{x}\{x}\{x} \{x}\{x}\{x}\{x}\{x}\{x}\{x}\{x}\{x}\{x}
+
+             \{x}\{x}\{x}\{x}\{x}\{x}\{x}\{x}\{x}\{x} \{x}\{x}\{x}\{x}\{x}\{x}\{x}\{x}\{x}\{x}
+             \{x}\{x}\{x}\{x}\{x}\{x}\{x}\{x}\{x}\{x} \{x}\{x}\{x}\{x}\{x}\{x}\{x}\{x}\{x}\{x}
+             \{x}\{x}\{x}\{x}\{x}\{x}\{x}\{x}\{x}\{x} \{x}\{x}\{x}\{x}\{x}\{x}\{x}\{x}\{x}\{x}
+             \{x}\{x}\{x}\{x}\{x}\{x}\{x}\{x}\{x}\{x} \{x}\{x}\{x}\{x}\{x}\{x}\{x}\{x}\{x}\{x}
+             \{x}\{x}\{x}\{x}\{x}\{x}\{x}\{x}\{x}\{x} \{x}\{x}\{x}\{x}\{x}\{x}\{x}\{x}\{x}\{x}
+
+             \{x}\{x}\{x}\{x}\{x}\{x}\{x}\{x}\{x}\{x} \{x}\{x}\{x}\{x}\{x}\{x}\{x}\{x}\{x}\{x}
+             \{x}\{x}\{x}\{x}\{x}\{x}\{x}\{x}\{x}\{x} \{x}\{x}\{x}\{x}\{x}\{x}\{x}\{x}\{x}\{x}
+             \{x}\{x}\{x}\{x}\{x}\{x}\{x}\{x}\{x}\{x} \{x}\{x}
+             """;
+        ASSERT(ts252.values().size(), 252);
+        ASSERT(ts252.interpolate(), """
+               9999999999 9999999999
+               9999999999 9999999999
+               9999999999 9999999999
+               9999999999 9999999999
+               9999999999 9999999999
+
+               9999999999 9999999999
+               9999999999 9999999999
+               9999999999 9999999999
+               9999999999 9999999999
+               9999999999 9999999999
+
+               9999999999 9999999999
+               9999999999 9999999999
+               9999999999 99
+               """);
+
+        StringTemplate ts253 = RAW."""
+             \{x}\{x}\{x}\{x}\{x}\{x}\{x}\{x}\{x}\{x} \{x}\{x}\{x}\{x}\{x}\{x}\{x}\{x}\{x}\{x}
+             \{x}\{x}\{x}\{x}\{x}\{x}\{x}\{x}\{x}\{x} \{x}\{x}\{x}\{x}\{x}\{x}\{x}\{x}\{x}\{x}
+             \{x}\{x}\{x}\{x}\{x}\{x}\{x}\{x}\{x}\{x} \{x}\{x}\{x}\{x}\{x}\{x}\{x}\{x}\{x}\{x}
+             \{x}\{x}\{x}\{x}\{x}\{x}\{x}\{x}\{x}\{x} \{x}\{x}\{x}\{x}\{x}\{x}\{x}\{x}\{x}\{x}
+             \{x}\{x}\{x}\{x}\{x}\{x}\{x}\{x}\{x}\{x} \{x}\{x}\{x}\{x}\{x}\{x}\{x}\{x}\{x}\{x}
+
+             \{x}\{x}\{x}\{x}\{x}\{x}\{x}\{x}\{x}\{x} \{x}\{x}\{x}\{x}\{x}\{x}\{x}\{x}\{x}\{x}
+             \{x}\{x}\{x}\{x}\{x}\{x}\{x}\{x}\{x}\{x} \{x}\{x}\{x}\{x}\{x}\{x}\{x}\{x}\{x}\{x}
+             \{x}\{x}\{x}\{x}\{x}\{x}\{x}\{x}\{x}\{x} \{x}\{x}\{x}\{x}\{x}\{x}\{x}\{x}\{x}\{x}
+             \{x}\{x}\{x}\{x}\{x}\{x}\{x}\{x}\{x}\{x} \{x}\{x}\{x}\{x}\{x}\{x}\{x}\{x}\{x}\{x}
+             \{x}\{x}\{x}\{x}\{x}\{x}\{x}\{x}\{x}\{x} \{x}\{x}\{x}\{x}\{x}\{x}\{x}\{x}\{x}\{x}
+
+             \{x}\{x}\{x}\{x}\{x}\{x}\{x}\{x}\{x}\{x} \{x}\{x}\{x}\{x}\{x}\{x}\{x}\{x}\{x}\{x}
+             \{x}\{x}\{x}\{x}\{x}\{x}\{x}\{x}\{x}\{x} \{x}\{x}\{x}\{x}\{x}\{x}\{x}\{x}\{x}\{x}
+             \{x}\{x}\{x}\{x}\{x}\{x}\{x}\{x}\{x}\{x} \{x}\{x}\{x}
+             """;
+        ASSERT(ts253.values().size(), 253);
+        ASSERT(ts253.interpolate(), """
+               9999999999 9999999999
+               9999999999 9999999999
+               9999999999 9999999999
+               9999999999 9999999999
+               9999999999 9999999999
+
+               9999999999 9999999999
+               9999999999 9999999999
+               9999999999 9999999999
+               9999999999 9999999999
+               9999999999 9999999999
+
+               9999999999 9999999999
+               9999999999 9999999999
+               9999999999 999
+               """);
+
+        StringTemplate ts254 = RAW."""
+             \{x}\{x}\{x}\{x}\{x}\{x}\{x}\{x}\{x}\{x} \{x}\{x}\{x}\{x}\{x}\{x}\{x}\{x}\{x}\{x}
+             \{x}\{x}\{x}\{x}\{x}\{x}\{x}\{x}\{x}\{x} \{x}\{x}\{x}\{x}\{x}\{x}\{x}\{x}\{x}\{x}
+             \{x}\{x}\{x}\{x}\{x}\{x}\{x}\{x}\{x}\{x} \{x}\{x}\{x}\{x}\{x}\{x}\{x}\{x}\{x}\{x}
+             \{x}\{x}\{x}\{x}\{x}\{x}\{x}\{x}\{x}\{x} \{x}\{x}\{x}\{x}\{x}\{x}\{x}\{x}\{x}\{x}
+             \{x}\{x}\{x}\{x}\{x}\{x}\{x}\{x}\{x}\{x} \{x}\{x}\{x}\{x}\{x}\{x}\{x}\{x}\{x}\{x}
+
+             \{x}\{x}\{x}\{x}\{x}\{x}\{x}\{x}\{x}\{x} \{x}\{x}\{x}\{x}\{x}\{x}\{x}\{x}\{x}\{x}
+             \{x}\{x}\{x}\{x}\{x}\{x}\{x}\{x}\{x}\{x} \{x}\{x}\{x}\{x}\{x}\{x}\{x}\{x}\{x}\{x}
+             \{x}\{x}\{x}\{x}\{x}\{x}\{x}\{x}\{x}\{x} \{x}\{x}\{x}\{x}\{x}\{x}\{x}\{x}\{x}\{x}
+             \{x}\{x}\{x}\{x}\{x}\{x}\{x}\{x}\{x}\{x} \{x}\{x}\{x}\{x}\{x}\{x}\{x}\{x}\{x}\{x}
+             \{x}\{x}\{x}\{x}\{x}\{x}\{x}\{x}\{x}\{x} \{x}\{x}\{x}\{x}\{x}\{x}\{x}\{x}\{x}\{x}
+
+             \{x}\{x}\{x}\{x}\{x}\{x}\{x}\{x}\{x}\{x} \{x}\{x}\{x}\{x}\{x}\{x}\{x}\{x}\{x}\{x}
+             \{x}\{x}\{x}\{x}\{x}\{x}\{x}\{x}\{x}\{x} \{x}\{x}\{x}\{x}\{x}\{x}\{x}\{x}\{x}\{x}
+             \{x}\{x}\{x}\{x}\{x}\{x}\{x}\{x}\{x}\{x} \{x}\{x}\{x}\{x}
+             """;
+        ASSERT(ts254.values().size(), 254);
+        ASSERT(ts254.interpolate(), """
+               9999999999 9999999999
+               9999999999 9999999999
+               9999999999 9999999999
+               9999999999 9999999999
+               9999999999 9999999999
+
+               9999999999 9999999999
+               9999999999 9999999999
+               9999999999 9999999999
+               9999999999 9999999999
+               9999999999 9999999999
+
+               9999999999 9999999999
+               9999999999 9999999999
+               9999999999 9999
+               """);
+
+        StringTemplate ts255 = RAW."""
+             \{x}\{x}\{x}\{x}\{x}\{x}\{x}\{x}\{x}\{x} \{x}\{x}\{x}\{x}\{x}\{x}\{x}\{x}\{x}\{x}
+             \{x}\{x}\{x}\{x}\{x}\{x}\{x}\{x}\{x}\{x} \{x}\{x}\{x}\{x}\{x}\{x}\{x}\{x}\{x}\{x}
+             \{x}\{x}\{x}\{x}\{x}\{x}\{x}\{x}\{x}\{x} \{x}\{x}\{x}\{x}\{x}\{x}\{x}\{x}\{x}\{x}
+             \{x}\{x}\{x}\{x}\{x}\{x}\{x}\{x}\{x}\{x} \{x}\{x}\{x}\{x}\{x}\{x}\{x}\{x}\{x}\{x}
+             \{x}\{x}\{x}\{x}\{x}\{x}\{x}\{x}\{x}\{x} \{x}\{x}\{x}\{x}\{x}\{x}\{x}\{x}\{x}\{x}
+
+             \{x}\{x}\{x}\{x}\{x}\{x}\{x}\{x}\{x}\{x} \{x}\{x}\{x}\{x}\{x}\{x}\{x}\{x}\{x}\{x}
+             \{x}\{x}\{x}\{x}\{x}\{x}\{x}\{x}\{x}\{x} \{x}\{x}\{x}\{x}\{x}\{x}\{x}\{x}\{x}\{x}
+             \{x}\{x}\{x}\{x}\{x}\{x}\{x}\{x}\{x}\{x} \{x}\{x}\{x}\{x}\{x}\{x}\{x}\{x}\{x}\{x}
+             \{x}\{x}\{x}\{x}\{x}\{x}\{x}\{x}\{x}\{x} \{x}\{x}\{x}\{x}\{x}\{x}\{x}\{x}\{x}\{x}
+             \{x}\{x}\{x}\{x}\{x}\{x}\{x}\{x}\{x}\{x} \{x}\{x}\{x}\{x}\{x}\{x}\{x}\{x}\{x}\{x}
+
+             \{x}\{x}\{x}\{x}\{x}\{x}\{x}\{x}\{x}\{x} \{x}\{x}\{x}\{x}\{x}\{x}\{x}\{x}\{x}\{x}
+             \{x}\{x}\{x}\{x}\{x}\{x}\{x}\{x}\{x}\{x} \{x}\{x}\{x}\{x}\{x}\{x}\{x}\{x}\{x}\{x}
+             \{x}\{x}\{x}\{x}\{x}\{x}\{x}\{x}\{x}\{x} \{x}\{x}\{x}\{x}\{x}
+             """;
+        ASSERT(ts255.values().size(), 255);
+        ASSERT(ts255.interpolate(), """
+               9999999999 9999999999
+               9999999999 9999999999
+               9999999999 9999999999
+               9999999999 9999999999
+               9999999999 9999999999
+
+               9999999999 9999999999
+               9999999999 9999999999
+               9999999999 9999999999
+               9999999999 9999999999
+               9999999999 9999999999
+
+               9999999999 9999999999
+               9999999999 9999999999
+               9999999999 99999
+               """);
+
+        StringTemplate ts256 = RAW."""
+             \{x}\{x}\{x}\{x}\{x}\{x}\{x}\{x}\{x}\{x} \{x}\{x}\{x}\{x}\{x}\{x}\{x}\{x}\{x}\{x}
+             \{x}\{x}\{x}\{x}\{x}\{x}\{x}\{x}\{x}\{x} \{x}\{x}\{x}\{x}\{x}\{x}\{x}\{x}\{x}\{x}
+             \{x}\{x}\{x}\{x}\{x}\{x}\{x}\{x}\{x}\{x} \{x}\{x}\{x}\{x}\{x}\{x}\{x}\{x}\{x}\{x}
+             \{x}\{x}\{x}\{x}\{x}\{x}\{x}\{x}\{x}\{x} \{x}\{x}\{x}\{x}\{x}\{x}\{x}\{x}\{x}\{x}
+             \{x}\{x}\{x}\{x}\{x}\{x}\{x}\{x}\{x}\{x} \{x}\{x}\{x}\{x}\{x}\{x}\{x}\{x}\{x}\{x}
+
+             \{x}\{x}\{x}\{x}\{x}\{x}\{x}\{x}\{x}\{x} \{x}\{x}\{x}\{x}\{x}\{x}\{x}\{x}\{x}\{x}
+             \{x}\{x}\{x}\{x}\{x}\{x}\{x}\{x}\{x}\{x} \{x}\{x}\{x}\{x}\{x}\{x}\{x}\{x}\{x}\{x}
+             \{x}\{x}\{x}\{x}\{x}\{x}\{x}\{x}\{x}\{x} \{x}\{x}\{x}\{x}\{x}\{x}\{x}\{x}\{x}\{x}
+             \{x}\{x}\{x}\{x}\{x}\{x}\{x}\{x}\{x}\{x} \{x}\{x}\{x}\{x}\{x}\{x}\{x}\{x}\{x}\{x}
+             \{x}\{x}\{x}\{x}\{x}\{x}\{x}\{x}\{x}\{x} \{x}\{x}\{x}\{x}\{x}\{x}\{x}\{x}\{x}\{x}
+
+             \{x}\{x}\{x}\{x}\{x}\{x}\{x}\{x}\{x}\{x} \{x}\{x}\{x}\{x}\{x}\{x}\{x}\{x}\{x}\{x}
+             \{x}\{x}\{x}\{x}\{x}\{x}\{x}\{x}\{x}\{x} \{x}\{x}\{x}\{x}\{x}\{x}\{x}\{x}\{x}\{x}
+             \{x}\{x}\{x}\{x}\{x}\{x}\{x}\{x}\{x}\{x} \{x}\{x}\{x}\{x}\{x}\{x}
+             """;
+        ASSERT(ts256.values().size(), 256);
+        ASSERT(ts256.interpolate(), """
+               9999999999 9999999999
+               9999999999 9999999999
+               9999999999 9999999999
+               9999999999 9999999999
+               9999999999 9999999999
+
+               9999999999 9999999999
+               9999999999 9999999999
+               9999999999 9999999999
+               9999999999 9999999999
+               9999999999 9999999999
+
+               9999999999 9999999999
+               9999999999 9999999999
+               9999999999 999999
+               """);
+
+    }
+
+    /*
+     * Processor tests.
+     */
+    public static final Processor<StringTemplate, RuntimeException> STRINGIFY = st -> {
+        List<Object> values = st.values()
+                .stream()
+                .map(v -> (Object)String.valueOf(v))
+                .toList();
+
+        return StringTemplate.of(st.fragments(), values);
+    };
+
+    public static final Processor<StringTemplate, RuntimeException> UPPER = st -> {
+        List<String> fragments = st.fragments()
+                .stream()
+                .map(String::toUpperCase)
+                .toList();
+
+        return StringTemplate.of(fragments, st.values());
+    };
+
+    public static final Processor<String, RuntimeException> CHAIN = st -> {
+        st = STRINGIFY.process(st);
+        st = UPPER.process(st);
+        return STR.process(st);
+    };
+
+    static void processorTests() {
+        String name = "Joan";
+        int age = 25;
+        ASSERT(CHAIN."\{name} is \{age} years old", "Joan IS 25 YEARS OLD");
+    }
+
+    /*
+     *  StringTemplate coverage
+     */
+    static void stringTemplateCoverage() {
+        StringTemplate tsNoValues = StringTemplate.of("No Values");
+
+        ASSERT(tsNoValues.values(), List.of());
+        ASSERT(tsNoValues.fragments(), List.of("No Values"));
+        ASSERT(tsNoValues.interpolate(), STR."No Values");
+
+        int x = 10, y = 20;
+        StringTemplate src = RAW."\{x} + \{y} = \{x + y}";
+        StringTemplate tsValues = StringTemplate.of(src.fragments(), src.values());
+        ASSERT(tsValues.fragments(), List.of("", " + ", " = ", ""));
+        ASSERT(tsValues.values(), List.of(x, y, x + y));
+        ASSERT(tsValues.interpolate(), x + " + " + y + " = " + (x + y));
+        ASSERT(StringTemplate.combine(src, src).interpolate(),
+                RAW."\{x} + \{y} = \{x + y}\{x} + \{y} = \{x + y}".interpolate());
+        ASSERT(StringTemplate.combine(src), src);
+        ASSERT(StringTemplate.combine().interpolate(), "");
+        ASSERT(StringTemplate.combine(List.of(src, src)).interpolate(),
+                RAW."\{x} + \{y} = \{x + y}\{x} + \{y} = \{x + y}".interpolate());
+    }
+
+    /*
+     * SimpleProcessor coverage.
+     */
+
+    static class Processor0 implements Processor<String, IllegalArgumentException> {
+        @Override
+        public String process(StringTemplate stringTemplate) throws IllegalArgumentException {
+            StringBuilder sb = new StringBuilder();
+            Iterator<String> fragmentsIter = stringTemplate.fragments().iterator();
+
+            for (Object value : stringTemplate.values()) {
+                sb.append(fragmentsIter.next());
+
+                if (value instanceof Boolean) {
+                    throw new IllegalArgumentException("I don't like Booleans");
+                }
+
+                sb.append(value);
+            }
+
+            sb.append(fragmentsIter.next());
+
+            return sb.toString();
+        }
+    }
+
+    static Processor0 processor0 = new Processor0();
+
+    static Processor<String, RuntimeException> processor1 =
+        st -> st.interpolate();
+
+    static Processor<String, RuntimeException> processor2 = st -> st.interpolate();
+
+    static Processor<String, RuntimeException> processor3 = st -> st.interpolate();
+
+    static Processor<String, RuntimeException> processor4 = st ->
+        StringTemplate.interpolate(st.fragments(), st.values());
+
+
+    static void simpleProcessorCoverage() {
+        try {
+            int x = 10;
+            int y = 20;
+            ASSERT(processor0."\{x} + \{y} = \{x + y}", "10 + 20 = 30");
+            ASSERT(processor1."\{x} + \{y} = \{x + y}", "10 + 20 = 30");
+            ASSERT(processor2."\{x} + \{y} = \{x + y}", "10 + 20 = 30");
+            ASSERT(processor3."\{x} + \{y} = \{x + y}", "10 + 20 = 30");
+            ASSERT(processor4."\{x} + \{y} = \{x + y}", "10 + 20 = 30");
+        } catch (IllegalArgumentException ex) {
+            throw new RuntimeException("processor fail");
+        }
+    }
+
+    static String justify(String string, int width) {
+        boolean leftJustify = width < 0;
+        int length = string.length();
+        width = Math.abs(width);
+        int diff = width - length;
+
+        if (diff < 0) {
+            string = "*".repeat(width);
+        } else if (0 < diff) {
+            if (leftJustify) {
+                string += " ".repeat(diff);
+            } else {
+                string = " ".repeat(diff) + string;
+            }
+        }
+
+        return string;
+    }
+
+}

test/jdk/java/lang/template/FormatterBuilder.java

@@ -0,0 +1,915 @@
+/*
+ * Copyright (c) 2023, Oracle and/or its affiliates. All rights reserved.
+ * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
+ *
+ * This code is free software; you can redistribute it and/or modify it
+ * under the terms of the GNU General Public License version 2 only, as
+ * published by the Free Software Foundation.
+ *
+ * This code is distributed in the hope that it will be useful, but WITHOUT
+ * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
+ * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
+ * version 2 for more details (a copy is included in the LICENSE file that
+ * accompanied this code).
+ *
+ * You should have received a copy of the GNU General Public License version
+ * 2 along with this work; if not, write to the Free Software Foundation,
+ * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
+ *
+ * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
+ * or visit www.oracle.com if you need additional information or have any
+ * questions.
+ */
+
+/*
+ * @test
+ * @bug 0000000
+ * @summary Exercise format builder.
+ * @enablePreview true
+ */
+
+import java.util.FormatProcessor;
+import java.util.Objects;
+import java.util.Locale;
+
+import static java.util.FormatProcessor.FMT;
+
+public class FormatterBuilder {
+    public static void main(String... args) {
+        Locale.setDefault(Locale.US);
+        suite(FMT);
+        Locale thai = Locale.forLanguageTag("th-TH-u-nu-thai");
+        FormatProcessor thaiFormat = FormatProcessor.create(thai);
+        Locale.setDefault(thai);
+        suite(thaiFormat);
+    }
+
+    static void test(String a, String b) {
+        if (!Objects.equals(a, b)) {
+            throw new RuntimeException("format and FMT do not match: " + a + " : " + b);
+        }
+    }
+
+    static void suite(FormatProcessor fmt) {
+        Object nullObject = null;
+        test(String.format("%b", false), fmt."%b\{false}");
+        test(String.format("%b", true), fmt."%b\{true}");
+        test(String.format("%10b", false), fmt."%10b\{false}");
+        test(String.format("%10b", true), fmt."%10b\{true}");
+        test(String.format("%-10b", false), fmt."%-10b\{false}");
+        test(String.format("%-10b", true), fmt."%-10b\{true}");
+        test(String.format("%B", false), fmt."%B\{false}");
+        test(String.format("%B", true), fmt."%B\{true}");
+        test(String.format("%10B", false), fmt."%10B\{false}");
+        test(String.format("%10B", true), fmt."%10B\{true}");
+        test(String.format("%-10B", false), fmt."%-10B\{false}");
+        test(String.format("%-10B", true), fmt."%-10B\{true}");
+
+        test(String.format("%h", 12345), fmt."%h\{12345}");
+        test(String.format("%h", 0xABCDE), fmt."%h\{0xABCDE}");
+        test(String.format("%10h", 12345), fmt."%10h\{12345}");
+        test(String.format("%10h", 0xABCDE), fmt."%10h\{0xABCDE}");
+        test(String.format("%-10h", 12345), fmt."%-10h\{12345}");
+        test(String.format("%-10h", 0xABCDE), fmt."%-10h\{0xABCDE}");
+        test(String.format("%H", 12345), fmt."%H\{12345}");
+        test(String.format("%H", 0xABCDE), fmt."%H\{0xABCDE}");
+        test(String.format("%10H", 12345), fmt."%10H\{12345}");
+        test(String.format("%10H", 0xABCDE), fmt."%10H\{0xABCDE}");
+        test(String.format("%-10H", 12345), fmt."%-10H\{12345}");
+        test(String.format("%-10H", 0xABCDE), fmt."%-10H\{0xABCDE}");
+
+        test(String.format("%s", (byte)0xFF), fmt."%s\{(byte)0xFF}");
+        test(String.format("%s", (short)0xFFFF), fmt."%s\{(short)0xFFFF}");
+        test(String.format("%s", 12345), fmt."%s\{12345}");
+        test(String.format("%s", 12345L), fmt."%s\{12345L}");
+        test(String.format("%s", 1.33f), fmt."%s\{1.33f}");
+        test(String.format("%s", 1.33), fmt."%s\{1.33}");
+        test(String.format("%s", "abcde"), fmt."%s\{"abcde"}");
+        test(String.format("%s", nullObject), fmt."%s\{nullObject}");
+        test(String.format("%10s", (byte)0xFF), fmt."%10s\{(byte)0xFF}");
+        test(String.format("%10s", (short)0xFFFF), fmt."%10s\{(short)0xFFFF}");
+        test(String.format("%10s", 12345), fmt."%10s\{12345}");
+        test(String.format("%10s", 12345L), fmt."%10s\{12345L}");
+        test(String.format("%10s", 1.33f), fmt."%10s\{1.33f}");
+        test(String.format("%10s", 1.33), fmt."%10s\{1.33}");
+        test(String.format("%10s", "abcde"), fmt."%10s\{"abcde"}");
+        test(String.format("%10s", nullObject), fmt."%10s\{nullObject}");
+        test(String.format("%-10s", (byte)0xFF), fmt."%-10s\{(byte)0xFF}");
+        test(String.format("%-10s", (short)0xFFFF), fmt."%-10s\{(short)0xFFFF}");
+        test(String.format("%-10s", 12345), fmt."%-10s\{12345}");
+        test(String.format("%-10s", 12345L), fmt."%-10s\{12345L}");
+        test(String.format("%-10s", 1.33f), fmt."%-10s\{1.33f}");
+        test(String.format("%-10s", 1.33), fmt."%-10s\{1.33}");
+        test(String.format("%-10s", "abcde"), fmt."%-10s\{"abcde"}");
+        test(String.format("%-10s", nullObject), fmt."%-10s\{nullObject}");
+        test(String.format("%S", (byte)0xFF), fmt."%S\{(byte)0xFF}");
+        test(String.format("%S", (short)0xFFFF), fmt."%S\{(short)0xFFFF}");
+        test(String.format("%S", 12345), fmt."%S\{12345}");
+        test(String.format("%S", 12345L), fmt."%S\{12345L}");
+        test(String.format("%S", 1.33f), fmt."%S\{1.33f}");
+        test(String.format("%S", 1.33), fmt."%S\{1.33}");
+        test(String.format("%S", "abcde"), fmt."%S\{"abcde"}");
+        test(String.format("%S", nullObject), fmt."%S\{nullObject}");
+        test(String.format("%10S", (byte)0xFF), fmt."%10S\{(byte)0xFF}");
+        test(String.format("%10S", (short)0xFFFF), fmt."%10S\{(short)0xFFFF}");
+        test(String.format("%10S", 12345), fmt."%10S\{12345}");
+        test(String.format("%10S", 12345L), fmt."%10S\{12345L}");
+        test(String.format("%10S", 1.33f), fmt."%10S\{1.33f}");
+        test(String.format("%10S", 1.33), fmt."%10S\{1.33}");
+        test(String.format("%10S", "abcde"), fmt."%10S\{"abcde"}");
+        test(String.format("%10S", nullObject), fmt."%10S\{nullObject}");
+        test(String.format("%-10S", (byte)0xFF), fmt."%-10S\{(byte)0xFF}");
+        test(String.format("%-10S", (short)0xFFFF), fmt."%-10S\{(short)0xFFFF}");
+        test(String.format("%-10S", 12345), fmt."%-10S\{12345}");
+        test(String.format("%-10S", 12345L), fmt."%-10S\{12345L}");
+        test(String.format("%-10S", 1.33f), fmt."%-10S\{1.33f}");
+        test(String.format("%-10S", 1.33), fmt."%-10S\{1.33}");
+        test(String.format("%-10S", "abcde"), fmt."%-10S\{"abcde"}");
+        test(String.format("%-10S", nullObject), fmt."%-10S\{nullObject}");
+
+        test(String.format("%c", 'a'), fmt."%c\{'a'}");
+        test(String.format("%10c", 'a'), fmt."%10c\{'a'}");
+        test(String.format("%-10c", 'a'), fmt."%-10c\{'a'}");
+        test(String.format("%C", 'a'), fmt."%C\{'a'}");
+        test(String.format("%10C", 'a'), fmt."%10C\{'a'}");
+        test(String.format("%-10C", 'a'), fmt."%-10C\{'a'}");
+
+        test(String.format("%d", -12345), fmt."%d\{-12345}");
+        test(String.format("%d", 0), fmt."%d\{0}");
+        test(String.format("%d", 12345), fmt."%d\{12345}");
+        test(String.format("%10d", -12345), fmt."%10d\{-12345}");
+        test(String.format("%10d", 0), fmt."%10d\{0}");
+        test(String.format("%10d", 12345), fmt."%10d\{12345}");
+        test(String.format("%-10d", -12345), fmt."%-10d\{-12345}");
+        test(String.format("%-10d", 0), fmt."%-10d\{0}");
+        test(String.format("%-10d", 12345), fmt."%-10d\{12345}");
+        test(String.format("%,d", -12345), fmt."%,d\{-12345}");
+        test(String.format("%,d", 0), fmt."%,d\{0}");
+        test(String.format("%,d", 12345), fmt."%,d\{12345}");
+        test(String.format("%,10d", -12345), fmt."%,10d\{-12345}");
+        test(String.format("%,10d", 0), fmt."%,10d\{0}");
+        test(String.format("%,10d", 12345), fmt."%,10d\{12345}");
+        test(String.format("%,-10d", -12345), fmt."%,-10d\{-12345}");
+        test(String.format("%,-10d", 0), fmt."%,-10d\{0}");
+        test(String.format("%,-10d", 12345), fmt."%,-10d\{12345}");
+        test(String.format("%010d", -12345), fmt."%010d\{-12345}");
+        test(String.format("%010d", 0), fmt."%010d\{0}");
+        test(String.format("%010d", 12345), fmt."%010d\{12345}");
+        test(String.format("%,010d", -12345), fmt."%,010d\{-12345}");
+        test(String.format("%,010d", 0), fmt."%,010d\{0}");
+        test(String.format("%,010d", 12345), fmt."%,010d\{12345}");
+
+        test(String.format("%d", -12345), fmt."%d\{-12345}");
+        test(String.format("%d", 0), fmt."%d\{0}");
+        test(String.format("%d", 12345), fmt."%d\{12345}");
+        test(String.format("%10d", -12345), fmt."%10d\{-12345}");
+        test(String.format("%10d", 0), fmt."%10d\{0}");
+        test(String.format("%10d", 12345), fmt."%10d\{12345}");
+        test(String.format("%-10d", -12345), fmt."%-10d\{-12345}");
+        test(String.format("%-10d", 0), fmt."%-10d\{0}");
+        test(String.format("%-10d", 12345), fmt."%-10d\{12345}");
+        test(String.format("%,d", -12345), fmt."%,d\{-12345}");
+        test(String.format("%,d", 0), fmt."%,d\{0}");
+        test(String.format("%,d", 12345), fmt."%,d\{12345}");
+        test(String.format("%,10d", -12345), fmt."%,10d\{-12345}");
+        test(String.format("%,10d", 0), fmt."%,10d\{0}");
+        test(String.format("%,10d", 12345), fmt."%,10d\{12345}");
+        test(String.format("%,-10d", -12345), fmt."%,-10d\{-12345}");
+        test(String.format("%,-10d", 0), fmt."%,-10d\{0}");
+        test(String.format("%,-10d", 12345), fmt."%,-10d\{12345}");
+        test(String.format("% d", -12345), fmt."% d\{-12345}");
+        test(String.format("% d", 0), fmt."% d\{0}");
+        test(String.format("% d", 12345), fmt."% d\{12345}");
+        test(String.format("% 10d", -12345), fmt."% 10d\{-12345}");
+        test(String.format("% 10d", 0), fmt."% 10d\{0}");
+        test(String.format("% 10d", 12345), fmt."% 10d\{12345}");
+        test(String.format("% -10d", -12345), fmt."% -10d\{-12345}");
+        test(String.format("% -10d", 0), fmt."% -10d\{0}");
+        test(String.format("% -10d", 12345), fmt."% -10d\{12345}");
+        test(String.format("%, d", -12345), fmt."%, d\{-12345}");
+        test(String.format("%, d", 0), fmt."%, d\{0}");
+        test(String.format("%, d", 12345), fmt."%, d\{12345}");
+        test(String.format("%, 10d", -12345), fmt."%, 10d\{-12345}");
+        test(String.format("%, 10d", 0), fmt."%, 10d\{0}");
+        test(String.format("%, 10d", 12345), fmt."%, 10d\{12345}");
+        test(String.format("%, -10d", -12345), fmt."%, -10d\{-12345}");
+        test(String.format("%, -10d", 0), fmt."%, -10d\{0}");
+        test(String.format("%, -10d", 12345), fmt."%, -10d\{12345}");
+        test(String.format("%010d", -12345), fmt."%010d\{-12345}");
+        test(String.format("%010d", 0), fmt."%010d\{0}");
+        test(String.format("%010d", 12345), fmt."%010d\{12345}");
+        test(String.format("%,010d", -12345), fmt."%,010d\{-12345}");
+        test(String.format("%,010d", 0), fmt."%,010d\{0}");
+        test(String.format("%,010d", 12345), fmt."%,010d\{12345}");
+        test(String.format("% 010d", -12345), fmt."% 010d\{-12345}");
+        test(String.format("% 010d", 0), fmt."% 010d\{0}");
+        test(String.format("% 010d", 12345), fmt."% 010d\{12345}");
+        test(String.format("%, 010d", -12345), fmt."%, 010d\{-12345}");
+        test(String.format("%, 010d", 0), fmt."%, 010d\{0}");
+        test(String.format("%, 010d", 12345), fmt."%, 010d\{12345}");
+
+        test(String.format("%d", -12345), fmt."%d\{-12345}");
+        test(String.format("%d", 0), fmt."%d\{0}");
+        test(String.format("%d", 12345), fmt."%d\{12345}");
+        test(String.format("%10d", -12345), fmt."%10d\{-12345}");
+        test(String.format("%10d", 0), fmt."%10d\{0}");
+        test(String.format("%10d", 12345), fmt."%10d\{12345}");
+        test(String.format("%-10d", -12345), fmt."%-10d\{-12345}");
+        test(String.format("%-10d", 0), fmt."%-10d\{0}");
+        test(String.format("%-10d", 12345), fmt."%-10d\{12345}");
+        test(String.format("%,d", -12345), fmt."%,d\{-12345}");
+        test(String.format("%,d", 0), fmt."%,d\{0}");
+        test(String.format("%,d", 12345), fmt."%,d\{12345}");
+        test(String.format("%,10d", -12345), fmt."%,10d\{-12345}");
+        test(String.format("%,10d", 0), fmt."%,10d\{0}");
+        test(String.format("%,10d", 12345), fmt."%,10d\{12345}");
+        test(String.format("%,-10d", -12345), fmt."%,-10d\{-12345}");
+        test(String.format("%,-10d", 0), fmt."%,-10d\{0}");
+        test(String.format("%,-10d", 12345), fmt."%,-10d\{12345}");
+        test(String.format("%+d", -12345), fmt."%+d\{-12345}");
+        test(String.format("%+d", 0), fmt."%+d\{0}");
+        test(String.format("%+d", 12345), fmt."%+d\{12345}");
+        test(String.format("%+10d", -12345), fmt."%+10d\{-12345}");
+        test(String.format("%+10d", 0), fmt."%+10d\{0}");
+        test(String.format("%+10d", 12345), fmt."%+10d\{12345}");
+        test(String.format("%+-10d", -12345), fmt."%+-10d\{-12345}");
+        test(String.format("%+-10d", 0), fmt."%+-10d\{0}");
+        test(String.format("%+-10d", 12345), fmt."%+-10d\{12345}");
+        test(String.format("%,+d", -12345), fmt."%,+d\{-12345}");
+        test(String.format("%,+d", 0), fmt."%,+d\{0}");
+        test(String.format("%,+d", 12345), fmt."%,+d\{12345}");
+        test(String.format("%,+10d", -12345), fmt."%,+10d\{-12345}");
+        test(String.format("%,+10d", 0), fmt."%,+10d\{0}");
+        test(String.format("%,+10d", 12345), fmt."%,+10d\{12345}");
+        test(String.format("%,+-10d", -12345), fmt."%,+-10d\{-12345}");
+        test(String.format("%,+-10d", 0), fmt."%,+-10d\{0}");
+        test(String.format("%,+-10d", 12345), fmt."%,+-10d\{12345}");
+        test(String.format("%010d", -12345), fmt."%010d\{-12345}");
+        test(String.format("%010d", 0), fmt."%010d\{0}");
+        test(String.format("%010d", 12345), fmt."%010d\{12345}");
+        test(String.format("%,010d", -12345), fmt."%,010d\{-12345}");
+        test(String.format("%,010d", 0), fmt."%,010d\{0}");
+        test(String.format("%,010d", 12345), fmt."%,010d\{12345}");
+        test(String.format("%+010d", -12345), fmt."%+010d\{-12345}");
+        test(String.format("%+010d", 0), fmt."%+010d\{0}");
+        test(String.format("%+010d", 12345), fmt."%+010d\{12345}");
+        test(String.format("%,+010d", -12345), fmt."%,+010d\{-12345}");
+        test(String.format("%,+010d", 0), fmt."%,+010d\{0}");
+        test(String.format("%,+010d", 12345), fmt."%,+010d\{12345}");
+
+        test(String.format("%d", -12345), fmt."%d\{-12345}");
+        test(String.format("%d", 0), fmt."%d\{0}");
+        test(String.format("%d", 12345), fmt."%d\{12345}");
+        test(String.format("%10d", -12345), fmt."%10d\{-12345}");
+        test(String.format("%10d", 0), fmt."%10d\{0}");
+        test(String.format("%10d", 12345), fmt."%10d\{12345}");
+        test(String.format("%-10d", -12345), fmt."%-10d\{-12345}");
+        test(String.format("%-10d", 0), fmt."%-10d\{0}");
+        test(String.format("%-10d", 12345), fmt."%-10d\{12345}");
+        test(String.format("%,d", -12345), fmt."%,d\{-12345}");
+        test(String.format("%,d", 0), fmt."%,d\{0}");
+        test(String.format("%,d", 12345), fmt."%,d\{12345}");
+        test(String.format("%,10d", -12345), fmt."%,10d\{-12345}");
+        test(String.format("%,10d", 0), fmt."%,10d\{0}");
+        test(String.format("%,10d", 12345), fmt."%,10d\{12345}");
+        test(String.format("%,-10d", -12345), fmt."%,-10d\{-12345}");
+        test(String.format("%,-10d", 0), fmt."%,-10d\{0}");
+        test(String.format("%,-10d", 12345), fmt."%,-10d\{12345}");
+        test(String.format("%(d", -12345), fmt."%(d\{-12345}");
+        test(String.format("%(d", 0), fmt."%(d\{0}");
+        test(String.format("%(d", 12345), fmt."%(d\{12345}");
+        test(String.format("%(10d", -12345), fmt."%(10d\{-12345}");
+        test(String.format("%(10d", 0), fmt."%(10d\{0}");
+        test(String.format("%(10d", 12345), fmt."%(10d\{12345}");
+        test(String.format("%(-10d", -12345), fmt."%(-10d\{-12345}");
+        test(String.format("%(-10d", 0), fmt."%(-10d\{0}");
+        test(String.format("%(-10d", 12345), fmt."%(-10d\{12345}");
+        test(String.format("%,(d", -12345), fmt."%,(d\{-12345}");
+        test(String.format("%,(d", 0), fmt."%,(d\{0}");
+        test(String.format("%,(d", 12345), fmt."%,(d\{12345}");
+        test(String.format("%,(10d", -12345), fmt."%,(10d\{-12345}");
+        test(String.format("%,(10d", 0), fmt."%,(10d\{0}");
+        test(String.format("%,(10d", 12345), fmt."%,(10d\{12345}");
+        test(String.format("%,(-10d", -12345), fmt."%,(-10d\{-12345}");
+        test(String.format("%,(-10d", 0), fmt."%,(-10d\{0}");
+        test(String.format("%,(-10d", 12345), fmt."%,(-10d\{12345}");
+        test(String.format("%010d", -12345), fmt."%010d\{-12345}");
+        test(String.format("%010d", 0), fmt."%010d\{0}");
+        test(String.format("%010d", 12345), fmt."%010d\{12345}");
+        test(String.format("%,010d", -12345), fmt."%,010d\{-12345}");
+        test(String.format("%,010d", 0), fmt."%,010d\{0}");
+        test(String.format("%,010d", 12345), fmt."%,010d\{12345}");
+        test(String.format("%(010d", -12345), fmt."%(010d\{-12345}");
+        test(String.format("%(010d", 0), fmt."%(010d\{0}");
+        test(String.format("%(010d", 12345), fmt."%(010d\{12345}");
+        test(String.format("%,(010d", -12345), fmt."%,(010d\{-12345}");
+        test(String.format("%,(010d", 0), fmt."%,(010d\{0}");
+        test(String.format("%,(010d", 12345), fmt."%,(010d\{12345}");
+
+        test(String.format("%o", -12345), fmt."%o\{-12345}");
+        test(String.format("%o", 0), fmt."%o\{0}");
+        test(String.format("%o", 12345), fmt."%o\{12345}");
+        test(String.format("%10o", -12345), fmt."%10o\{-12345}");
+        test(String.format("%10o", 0), fmt."%10o\{0}");
+        test(String.format("%10o", 12345), fmt."%10o\{12345}");
+        test(String.format("%-10o", -12345), fmt."%-10o\{-12345}");
+        test(String.format("%-10o", 0), fmt."%-10o\{0}");
+        test(String.format("%-10o", 12345), fmt."%-10o\{12345}");
+        test(String.format("%#o", -12345), fmt."%#o\{-12345}");
+        test(String.format("%#o", 0), fmt."%#o\{0}");
+        test(String.format("%#o", 12345), fmt."%#o\{12345}");
+        test(String.format("%#10o", -12345), fmt."%#10o\{-12345}");
+        test(String.format("%#10o", 0), fmt."%#10o\{0}");
+        test(String.format("%#10o", 12345), fmt."%#10o\{12345}");
+        test(String.format("%#-10o", -12345), fmt."%#-10o\{-12345}");
+        test(String.format("%#-10o", 0), fmt."%#-10o\{0}");
+        test(String.format("%#-10o", 12345), fmt."%#-10o\{12345}");
+        test(String.format("%010o", -12345), fmt."%010o\{-12345}");
+        test(String.format("%010o", 0), fmt."%010o\{0}");
+        test(String.format("%010o", 12345), fmt."%010o\{12345}");
+        test(String.format("%#010o", -12345), fmt."%#010o\{-12345}");
+        test(String.format("%#010o", 0), fmt."%#010o\{0}");
+        test(String.format("%#010o", 12345), fmt."%#010o\{12345}");
+
+        test(String.format("%x", -12345), fmt."%x\{-12345}");
+        test(String.format("%x", 0), fmt."%x\{0}");
+        test(String.format("%x", 12345), fmt."%x\{12345}");
+        test(String.format("%10x", -12345), fmt."%10x\{-12345}");
+        test(String.format("%10x", 0), fmt."%10x\{0}");
+        test(String.format("%10x", 12345), fmt."%10x\{12345}");
+        test(String.format("%-10x", -12345), fmt."%-10x\{-12345}");
+        test(String.format("%-10x", 0), fmt."%-10x\{0}");
+        test(String.format("%-10x", 12345), fmt."%-10x\{12345}");
+        test(String.format("%X", -12345), fmt."%X\{-12345}");
+        test(String.format("%X", 0), fmt."%X\{0}");
+        test(String.format("%X", 12345), fmt."%X\{12345}");
+        test(String.format("%10X", -12345), fmt."%10X\{-12345}");
+        test(String.format("%10X", 0), fmt."%10X\{0}");
+        test(String.format("%10X", 12345), fmt."%10X\{12345}");
+        test(String.format("%-10X", -12345), fmt."%-10X\{-12345}");
+        test(String.format("%-10X", 0), fmt."%-10X\{0}");
+        test(String.format("%-10X", 12345), fmt."%-10X\{12345}");
+        test(String.format("%#x", -12345), fmt."%#x\{-12345}");
+        test(String.format("%#x", 0), fmt."%#x\{0}");
+        test(String.format("%#x", 12345), fmt."%#x\{12345}");
+        test(String.format("%#10x", -12345), fmt."%#10x\{-12345}");
+        test(String.format("%#10x", 0), fmt."%#10x\{0}");
+        test(String.format("%#10x", 12345), fmt."%#10x\{12345}");
+        test(String.format("%#-10x", -12345), fmt."%#-10x\{-12345}");
+        test(String.format("%#-10x", 0), fmt."%#-10x\{0}");
+        test(String.format("%#-10x", 12345), fmt."%#-10x\{12345}");
+        test(String.format("%#X", -12345), fmt."%#X\{-12345}");
+        test(String.format("%#X", 0), fmt."%#X\{0}");
+        test(String.format("%#X", 12345), fmt."%#X\{12345}");
+        test(String.format("%#10X", -12345), fmt."%#10X\{-12345}");
+        test(String.format("%#10X", 0), fmt."%#10X\{0}");
+        test(String.format("%#10X", 12345), fmt."%#10X\{12345}");
+        test(String.format("%#-10X", -12345), fmt."%#-10X\{-12345}");
+        test(String.format("%#-10X", 0), fmt."%#-10X\{0}");
+        test(String.format("%#-10X", 12345), fmt."%#-10X\{12345}");
+        test(String.format("%010x", -12345), fmt."%010x\{-12345}");
+        test(String.format("%010x", 0), fmt."%010x\{0}");
+        test(String.format("%010x", 12345), fmt."%010x\{12345}");
+        test(String.format("%010X", -12345), fmt."%010X\{-12345}");
+        test(String.format("%010X", 0), fmt."%010X\{0}");
+        test(String.format("%010X", 12345), fmt."%010X\{12345}");
+        test(String.format("%#010x", -12345), fmt."%#010x\{-12345}");
+        test(String.format("%#010x", 0), fmt."%#010x\{0}");
+        test(String.format("%#010x", 12345), fmt."%#010x\{12345}");
+        test(String.format("%#010X", -12345), fmt."%#010X\{-12345}");
+        test(String.format("%#010X", 0), fmt."%#010X\{0}");
+        test(String.format("%#010X", 12345), fmt."%#010X\{12345}");
+
+        test(String.format("%f", -12345.6), fmt."%f\{-12345.6}");
+        test(String.format("%f", 0.0), fmt."%f\{0.0}");
+        test(String.format("%f", 12345.6), fmt."%f\{12345.6}");
+        test(String.format("%10f", -12345.6), fmt."%10f\{-12345.6}");
+        test(String.format("%10f", 0.0), fmt."%10f\{0.0}");
+        test(String.format("%10f", 12345.6), fmt."%10f\{12345.6}");
+        test(String.format("%-10f", -12345.6), fmt."%-10f\{-12345.6}");
+        test(String.format("%-10f", 0.0), fmt."%-10f\{0.0}");
+        test(String.format("%-10f", 12345.6), fmt."%-10f\{12345.6}");
+        test(String.format("%,f", -12345.6), fmt."%,f\{-12345.6}");
+        test(String.format("%,f", 0.0), fmt."%,f\{0.0}");
+        test(String.format("%,f", 12345.6), fmt."%,f\{12345.6}");
+        test(String.format("%,10f", -12345.6), fmt."%,10f\{-12345.6}");
+        test(String.format("%,10f", 0.0), fmt."%,10f\{0.0}");
+        test(String.format("%,10f", 12345.6), fmt."%,10f\{12345.6}");
+        test(String.format("%,-10f", -12345.6), fmt."%,-10f\{-12345.6}");
+        test(String.format("%,-10f", 0.0), fmt."%,-10f\{0.0}");
+        test(String.format("%,-10f", 12345.6), fmt."%,-10f\{12345.6}");
+
+        test(String.format("%f", -12345.6), fmt."%f\{-12345.6}");
+        test(String.format("%f", 0.0), fmt."%f\{0.0}");
+        test(String.format("%f", 12345.6), fmt."%f\{12345.6}");
+        test(String.format("%10f", -12345.6), fmt."%10f\{-12345.6}");
+        test(String.format("%10f", 0.0), fmt."%10f\{0.0}");
+        test(String.format("%10f", 12345.6), fmt."%10f\{12345.6}");
+        test(String.format("%-10f", -12345.6), fmt."%-10f\{-12345.6}");
+        test(String.format("%-10f", 0.0), fmt."%-10f\{0.0}");
+        test(String.format("%-10f", 12345.6), fmt."%-10f\{12345.6}");
+        test(String.format("%,f", -12345.6), fmt."%,f\{-12345.6}");
+        test(String.format("%,f", 0.0), fmt."%,f\{0.0}");
+        test(String.format("%,f", 12345.6), fmt."%,f\{12345.6}");
+        test(String.format("%,10f", -12345.6), fmt."%,10f\{-12345.6}");
+        test(String.format("%,10f", 0.0), fmt."%,10f\{0.0}");
+        test(String.format("%,10f", 12345.6), fmt."%,10f\{12345.6}");
+        test(String.format("%,-10f", -12345.6), fmt."%,-10f\{-12345.6}");
+        test(String.format("%,-10f", 0.0), fmt."%,-10f\{0.0}");
+        test(String.format("%,-10f", 12345.6), fmt."%,-10f\{12345.6}");
+        test(String.format("% f", -12345.6), fmt."% f\{-12345.6}");
+        test(String.format("% f", 0.0), fmt."% f\{0.0}");
+        test(String.format("% f", 12345.6), fmt."% f\{12345.6}");
+        test(String.format("% 10f", -12345.6), fmt."% 10f\{-12345.6}");
+        test(String.format("% 10f", 0.0), fmt."% 10f\{0.0}");
+        test(String.format("% 10f", 12345.6), fmt."% 10f\{12345.6}");
+        test(String.format("% -10f", -12345.6), fmt."% -10f\{-12345.6}");
+        test(String.format("% -10f", 0.0), fmt."% -10f\{0.0}");
+        test(String.format("% -10f", 12345.6), fmt."% -10f\{12345.6}");
+        test(String.format("%, f", -12345.6), fmt."%, f\{-12345.6}");
+        test(String.format("%, f", 0.0), fmt."%, f\{0.0}");
+        test(String.format("%, f", 12345.6), fmt."%, f\{12345.6}");
+        test(String.format("%, 10f", -12345.6), fmt."%, 10f\{-12345.6}");
+        test(String.format("%, 10f", 0.0), fmt."%, 10f\{0.0}");
+        test(String.format("%, 10f", 12345.6), fmt."%, 10f\{12345.6}");
+        test(String.format("%, -10f", -12345.6), fmt."%, -10f\{-12345.6}");
+        test(String.format("%, -10f", 0.0), fmt."%, -10f\{0.0}");
+        test(String.format("%, -10f", 12345.6), fmt."%, -10f\{12345.6}");
+
+        test(String.format("%f", -12345.6), fmt."%f\{-12345.6}");
+        test(String.format("%f", 0.0), fmt."%f\{0.0}");
+        test(String.format("%f", 12345.6), fmt."%f\{12345.6}");
+        test(String.format("%10f", -12345.6), fmt."%10f\{-12345.6}");
+        test(String.format("%10f", 0.0), fmt."%10f\{0.0}");
+        test(String.format("%10f", 12345.6), fmt."%10f\{12345.6}");
+        test(String.format("%-10f", -12345.6), fmt."%-10f\{-12345.6}");
+        test(String.format("%-10f", 0.0), fmt."%-10f\{0.0}");
+        test(String.format("%-10f", 12345.6), fmt."%-10f\{12345.6}");
+        test(String.format("%,f", -12345.6), fmt."%,f\{-12345.6}");
+        test(String.format("%,f", 0.0), fmt."%,f\{0.0}");
+        test(String.format("%,f", 12345.6), fmt."%,f\{12345.6}");
+        test(String.format("%,10f", -12345.6), fmt."%,10f\{-12345.6}");
+        test(String.format("%,10f", 0.0), fmt."%,10f\{0.0}");
+        test(String.format("%,10f", 12345.6), fmt."%,10f\{12345.6}");
+        test(String.format("%,-10f", -12345.6), fmt."%,-10f\{-12345.6}");
+        test(String.format("%,-10f", 0.0), fmt."%,-10f\{0.0}");
+        test(String.format("%,-10f", 12345.6), fmt."%,-10f\{12345.6}");
+        test(String.format("%+f", -12345.6), fmt."%+f\{-12345.6}");
+        test(String.format("%+f", 0.0), fmt."%+f\{0.0}");
+        test(String.format("%+f", 12345.6), fmt."%+f\{12345.6}");
+        test(String.format("%+10f", -12345.6), fmt."%+10f\{-12345.6}");
+        test(String.format("%+10f", 0.0), fmt."%+10f\{0.0}");
+        test(String.format("%+10f", 12345.6), fmt."%+10f\{12345.6}");
+        test(String.format("%+-10f", -12345.6), fmt."%+-10f\{-12345.6}");
+        test(String.format("%+-10f", 0.0), fmt."%+-10f\{0.0}");
+        test(String.format("%+-10f", 12345.6), fmt."%+-10f\{12345.6}");
+        test(String.format("%,+f", -12345.6), fmt."%,+f\{-12345.6}");
+        test(String.format("%,+f", 0.0), fmt."%,+f\{0.0}");
+        test(String.format("%,+f", 12345.6), fmt."%,+f\{12345.6}");
+        test(String.format("%,+10f", -12345.6), fmt."%,+10f\{-12345.6}");
+        test(String.format("%,+10f", 0.0), fmt."%,+10f\{0.0}");
+        test(String.format("%,+10f", 12345.6), fmt."%,+10f\{12345.6}");
+        test(String.format("%,+-10f", -12345.6), fmt."%,+-10f\{-12345.6}");
+        test(String.format("%,+-10f", 0.0), fmt."%,+-10f\{0.0}");
+        test(String.format("%,+-10f", 12345.6), fmt."%,+-10f\{12345.6}");
+
+        test(String.format("%f", -12345.6), fmt."%f\{-12345.6}");
+        test(String.format("%f", 0.0), fmt."%f\{0.0}");
+        test(String.format("%f", 12345.6), fmt."%f\{12345.6}");
+        test(String.format("%10f", -12345.6), fmt."%10f\{-12345.6}");
+        test(String.format("%10f", 0.0), fmt."%10f\{0.0}");
+        test(String.format("%10f", 12345.6), fmt."%10f\{12345.6}");
+        test(String.format("%-10f", -12345.6), fmt."%-10f\{-12345.6}");
+        test(String.format("%-10f", 0.0), fmt."%-10f\{0.0}");
+        test(String.format("%-10f", 12345.6), fmt."%-10f\{12345.6}");
+        test(String.format("%,f", -12345.6), fmt."%,f\{-12345.6}");
+        test(String.format("%,f", 0.0), fmt."%,f\{0.0}");
+        test(String.format("%,f", 12345.6), fmt."%,f\{12345.6}");
+        test(String.format("%,10f", -12345.6), fmt."%,10f\{-12345.6}");
+        test(String.format("%,10f", 0.0), fmt."%,10f\{0.0}");
+        test(String.format("%,10f", 12345.6), fmt."%,10f\{12345.6}");
+        test(String.format("%,-10f", -12345.6), fmt."%,-10f\{-12345.6}");
+        test(String.format("%,-10f", 0.0), fmt."%,-10f\{0.0}");
+        test(String.format("%,-10f", 12345.6), fmt."%,-10f\{12345.6}");
+        test(String.format("%(f", -12345.6), fmt."%(f\{-12345.6}");
+        test(String.format("%(f", 0.0), fmt."%(f\{0.0}");
+        test(String.format("%(f", 12345.6), fmt."%(f\{12345.6}");
+        test(String.format("%(10f", -12345.6), fmt."%(10f\{-12345.6}");
+        test(String.format("%(10f", 0.0), fmt."%(10f\{0.0}");
+        test(String.format("%(10f", 12345.6), fmt."%(10f\{12345.6}");
+        test(String.format("%(-10f", -12345.6), fmt."%(-10f\{-12345.6}");
+        test(String.format("%(-10f", 0.0), fmt."%(-10f\{0.0}");
+        test(String.format("%(-10f", 12345.6), fmt."%(-10f\{12345.6}");
+        test(String.format("%,(f", -12345.6), fmt."%,(f\{-12345.6}");
+        test(String.format("%,(f", 0.0), fmt."%,(f\{0.0}");
+        test(String.format("%,(f", 12345.6), fmt."%,(f\{12345.6}");
+        test(String.format("%,(10f", -12345.6), fmt."%,(10f\{-12345.6}");
+        test(String.format("%,(10f", 0.0), fmt."%,(10f\{0.0}");
+        test(String.format("%,(10f", 12345.6), fmt."%,(10f\{12345.6}");
+        test(String.format("%,(-10f", -12345.6), fmt."%,(-10f\{-12345.6}");
+        test(String.format("%,(-10f", 0.0), fmt."%,(-10f\{0.0}");
+        test(String.format("%,(-10f", 12345.6), fmt."%,(-10f\{12345.6}");
+        test(String.format("%+f", -12345.6), fmt."%+f\{-12345.6}");
+        test(String.format("%+f", 0.0), fmt."%+f\{0.0}");
+        test(String.format("%+f", 12345.6), fmt."%+f\{12345.6}");
+        test(String.format("%+10f", -12345.6), fmt."%+10f\{-12345.6}");
+        test(String.format("%+10f", 0.0), fmt."%+10f\{0.0}");
+        test(String.format("%+10f", 12345.6), fmt."%+10f\{12345.6}");
+        test(String.format("%+-10f", -12345.6), fmt."%+-10f\{-12345.6}");
+        test(String.format("%+-10f", 0.0), fmt."%+-10f\{0.0}");
+        test(String.format("%+-10f", 12345.6), fmt."%+-10f\{12345.6}");
+        test(String.format("%,+f", -12345.6), fmt."%,+f\{-12345.6}");
+        test(String.format("%,+f", 0.0), fmt."%,+f\{0.0}");
+        test(String.format("%,+f", 12345.6), fmt."%,+f\{12345.6}");
+        test(String.format("%,+10f", -12345.6), fmt."%,+10f\{-12345.6}");
+        test(String.format("%,+10f", 0.0), fmt."%,+10f\{0.0}");
+        test(String.format("%,+10f", 12345.6), fmt."%,+10f\{12345.6}");
+        test(String.format("%,+-10f", -12345.6), fmt."%,+-10f\{-12345.6}");
+        test(String.format("%,+-10f", 0.0), fmt."%,+-10f\{0.0}");
+        test(String.format("%,+-10f", 12345.6), fmt."%,+-10f\{12345.6}");
+        test(String.format("%(+f", -12345.6), fmt."%(+f\{-12345.6}");
+        test(String.format("%(+f", 0.0), fmt."%(+f\{0.0}");
+        test(String.format("%(+f", 12345.6), fmt."%(+f\{12345.6}");
+        test(String.format("%(+10f", -12345.6), fmt."%(+10f\{-12345.6}");
+        test(String.format("%(+10f", 0.0), fmt."%(+10f\{0.0}");
+        test(String.format("%(+10f", 12345.6), fmt."%(+10f\{12345.6}");
+        test(String.format("%(+-10f", -12345.6), fmt."%(+-10f\{-12345.6}");
+        test(String.format("%(+-10f", 0.0), fmt."%(+-10f\{0.0}");
+        test(String.format("%(+-10f", 12345.6), fmt."%(+-10f\{12345.6}");
+        test(String.format("%,(+f", -12345.6), fmt."%,(+f\{-12345.6}");
+        test(String.format("%,(+f", 0.0), fmt."%,(+f\{0.0}");
+        test(String.format("%,(+f", 12345.6), fmt."%,(+f\{12345.6}");
+        test(String.format("%,(+10f", -12345.6), fmt."%,(+10f\{-12345.6}");
+        test(String.format("%,(+10f", 0.0), fmt."%,(+10f\{0.0}");
+        test(String.format("%,(+10f", 12345.6), fmt."%,(+10f\{12345.6}");
+        test(String.format("%,(+-10f", -12345.6), fmt."%,(+-10f\{-12345.6}");
+        test(String.format("%,(+-10f", 0.0), fmt."%,(+-10f\{0.0}");
+        test(String.format("%,(+-10f", 12345.6), fmt."%,(+-10f\{12345.6}");
+
+        test(String.format("%e", -12345.6), fmt."%e\{-12345.6}");
+        test(String.format("%e", 0.0), fmt."%e\{0.0}");
+        test(String.format("%e", 12345.6), fmt."%e\{12345.6}");
+        test(String.format("%10e", -12345.6), fmt."%10e\{-12345.6}");
+        test(String.format("%10e", 0.0), fmt."%10e\{0.0}");
+        test(String.format("%10e", 12345.6), fmt."%10e\{12345.6}");
+        test(String.format("%-10e", -12345.6), fmt."%-10e\{-12345.6}");
+        test(String.format("%-10e", 0.0), fmt."%-10e\{0.0}");
+        test(String.format("%-10e", 12345.6), fmt."%-10e\{12345.6}");
+        test(String.format("%E", -12345.6), fmt."%E\{-12345.6}");
+        test(String.format("%E", 0.0), fmt."%E\{0.0}");
+        test(String.format("%E", 12345.6), fmt."%E\{12345.6}");
+        test(String.format("%10E", -12345.6), fmt."%10E\{-12345.6}");
+        test(String.format("%10E", 0.0), fmt."%10E\{0.0}");
+        test(String.format("%10E", 12345.6), fmt."%10E\{12345.6}");
+        test(String.format("%-10E", -12345.6), fmt."%-10E\{-12345.6}");
+        test(String.format("%-10E", 0.0), fmt."%-10E\{0.0}");
+        test(String.format("%-10E", 12345.6), fmt."%-10E\{12345.6}");
+
+        test(String.format("%g", -12345.6), fmt."%g\{-12345.6}");
+        test(String.format("%g", 0.0), fmt."%g\{0.0}");
+        test(String.format("%g", 12345.6), fmt."%g\{12345.6}");
+        test(String.format("%10g", -12345.6), fmt."%10g\{-12345.6}");
+        test(String.format("%10g", 0.0), fmt."%10g\{0.0}");
+        test(String.format("%10g", 12345.6), fmt."%10g\{12345.6}");
+        test(String.format("%-10g", -12345.6), fmt."%-10g\{-12345.6}");
+        test(String.format("%-10g", 0.0), fmt."%-10g\{0.0}");
+        test(String.format("%-10g", 12345.6), fmt."%-10g\{12345.6}");
+        test(String.format("%G", -12345.6), fmt."%G\{-12345.6}");
+        test(String.format("%G", 0.0), fmt."%G\{0.0}");
+        test(String.format("%G", 12345.6), fmt."%G\{12345.6}");
+        test(String.format("%10G", -12345.6), fmt."%10G\{-12345.6}");
+        test(String.format("%10G", 0.0), fmt."%10G\{0.0}");
+        test(String.format("%10G", 12345.6), fmt."%10G\{12345.6}");
+        test(String.format("%-10G", -12345.6), fmt."%-10G\{-12345.6}");
+        test(String.format("%-10G", 0.0), fmt."%-10G\{0.0}");
+        test(String.format("%-10G", 12345.6), fmt."%-10G\{12345.6}");
+        test(String.format("%,g", -12345.6), fmt."%,g\{-12345.6}");
+        test(String.format("%,g", 0.0), fmt."%,g\{0.0}");
+        test(String.format("%,g", 12345.6), fmt."%,g\{12345.6}");
+        test(String.format("%,10g", -12345.6), fmt."%,10g\{-12345.6}");
+        test(String.format("%,10g", 0.0), fmt."%,10g\{0.0}");
+        test(String.format("%,10g", 12345.6), fmt."%,10g\{12345.6}");
+        test(String.format("%,-10g", -12345.6), fmt."%,-10g\{-12345.6}");
+        test(String.format("%,-10g", 0.0), fmt."%,-10g\{0.0}");
+        test(String.format("%,-10g", 12345.6), fmt."%,-10g\{12345.6}");
+        test(String.format("%,G", -12345.6), fmt."%,G\{-12345.6}");
+        test(String.format("%,G", 0.0), fmt."%,G\{0.0}");
+        test(String.format("%,G", 12345.6), fmt."%,G\{12345.6}");
+        test(String.format("%,10G", -12345.6), fmt."%,10G\{-12345.6}");
+        test(String.format("%,10G", 0.0), fmt."%,10G\{0.0}");
+        test(String.format("%,10G", 12345.6), fmt."%,10G\{12345.6}");
+        test(String.format("%,-10G", -12345.6), fmt."%,-10G\{-12345.6}");
+        test(String.format("%,-10G", 0.0), fmt."%,-10G\{0.0}");
+        test(String.format("%,-10G", 12345.6), fmt."%,-10G\{12345.6}");
+
+        test(String.format("%g", -12345.6), fmt."%g\{-12345.6}");
+        test(String.format("%g", 0.0), fmt."%g\{0.0}");
+        test(String.format("%g", 12345.6), fmt."%g\{12345.6}");
+        test(String.format("%10g", -12345.6), fmt."%10g\{-12345.6}");
+        test(String.format("%10g", 0.0), fmt."%10g\{0.0}");
+        test(String.format("%10g", 12345.6), fmt."%10g\{12345.6}");
+        test(String.format("%-10g", -12345.6), fmt."%-10g\{-12345.6}");
+        test(String.format("%-10g", 0.0), fmt."%-10g\{0.0}");
+        test(String.format("%-10g", 12345.6), fmt."%-10g\{12345.6}");
+        test(String.format("%G", -12345.6), fmt."%G\{-12345.6}");
+        test(String.format("%G", 0.0), fmt."%G\{0.0}");
+        test(String.format("%G", 12345.6), fmt."%G\{12345.6}");
+        test(String.format("%10G", -12345.6), fmt."%10G\{-12345.6}");
+        test(String.format("%10G", 0.0), fmt."%10G\{0.0}");
+        test(String.format("%10G", 12345.6), fmt."%10G\{12345.6}");
+        test(String.format("%-10G", -12345.6), fmt."%-10G\{-12345.6}");
+        test(String.format("%-10G", 0.0), fmt."%-10G\{0.0}");
+        test(String.format("%-10G", 12345.6), fmt."%-10G\{12345.6}");
+        test(String.format("%,g", -12345.6), fmt."%,g\{-12345.6}");
+        test(String.format("%,g", 0.0), fmt."%,g\{0.0}");
+        test(String.format("%,g", 12345.6), fmt."%,g\{12345.6}");
+        test(String.format("%,10g", -12345.6), fmt."%,10g\{-12345.6}");
+        test(String.format("%,10g", 0.0), fmt."%,10g\{0.0}");
+        test(String.format("%,10g", 12345.6), fmt."%,10g\{12345.6}");
+        test(String.format("%,-10g", -12345.6), fmt."%,-10g\{-12345.6}");
+        test(String.format("%,-10g", 0.0), fmt."%,-10g\{0.0}");
+        test(String.format("%,-10g", 12345.6), fmt."%,-10g\{12345.6}");
+        test(String.format("%,G", -12345.6), fmt."%,G\{-12345.6}");
+        test(String.format("%,G", 0.0), fmt."%,G\{0.0}");
+        test(String.format("%,G", 12345.6), fmt."%,G\{12345.6}");
+        test(String.format("%,10G", -12345.6), fmt."%,10G\{-12345.6}");
+        test(String.format("%,10G", 0.0), fmt."%,10G\{0.0}");
+        test(String.format("%,10G", 12345.6), fmt."%,10G\{12345.6}");
+        test(String.format("%,-10G", -12345.6), fmt."%,-10G\{-12345.6}");
+        test(String.format("%,-10G", 0.0), fmt."%,-10G\{0.0}");
+        test(String.format("%,-10G", 12345.6), fmt."%,-10G\{12345.6}");
+        test(String.format("% g", -12345.6), fmt."% g\{-12345.6}");
+        test(String.format("% g", 0.0), fmt."% g\{0.0}");
+        test(String.format("% g", 12345.6), fmt."% g\{12345.6}");
+        test(String.format("% 10g", -12345.6), fmt."% 10g\{-12345.6}");
+        test(String.format("% 10g", 0.0), fmt."% 10g\{0.0}");
+        test(String.format("% 10g", 12345.6), fmt."% 10g\{12345.6}");
+        test(String.format("% -10g", -12345.6), fmt."% -10g\{-12345.6}");
+        test(String.format("% -10g", 0.0), fmt."% -10g\{0.0}");
+        test(String.format("% -10g", 12345.6), fmt."% -10g\{12345.6}");
+        test(String.format("% G", -12345.6), fmt."% G\{-12345.6}");
+        test(String.format("% G", 0.0), fmt."% G\{0.0}");
+        test(String.format("% G", 12345.6), fmt."% G\{12345.6}");
+        test(String.format("% 10G", -12345.6), fmt."% 10G\{-12345.6}");
+        test(String.format("% 10G", 0.0), fmt."% 10G\{0.0}");
+        test(String.format("% 10G", 12345.6), fmt."% 10G\{12345.6}");
+        test(String.format("% -10G", -12345.6), fmt."% -10G\{-12345.6}");
+        test(String.format("% -10G", 0.0), fmt."% -10G\{0.0}");
+        test(String.format("% -10G", 12345.6), fmt."% -10G\{12345.6}");
+        test(String.format("%, g", -12345.6), fmt."%, g\{-12345.6}");
+        test(String.format("%, g", 0.0), fmt."%, g\{0.0}");
+        test(String.format("%, g", 12345.6), fmt."%, g\{12345.6}");
+        test(String.format("%, 10g", -12345.6), fmt."%, 10g\{-12345.6}");
+        test(String.format("%, 10g", 0.0), fmt."%, 10g\{0.0}");
+        test(String.format("%, 10g", 12345.6), fmt."%, 10g\{12345.6}");
+        test(String.format("%, -10g", -12345.6), fmt."%, -10g\{-12345.6}");
+        test(String.format("%, -10g", 0.0), fmt."%, -10g\{0.0}");
+        test(String.format("%, -10g", 12345.6), fmt."%, -10g\{12345.6}");
+        test(String.format("%, G", -12345.6), fmt."%, G\{-12345.6}");
+        test(String.format("%, G", 0.0), fmt."%, G\{0.0}");
+        test(String.format("%, G", 12345.6), fmt."%, G\{12345.6}");
+        test(String.format("%, 10G", -12345.6), fmt."%, 10G\{-12345.6}");
+        test(String.format("%, 10G", 0.0), fmt."%, 10G\{0.0}");
+        test(String.format("%, 10G", 12345.6), fmt."%, 10G\{12345.6}");
+        test(String.format("%, -10G", -12345.6), fmt."%, -10G\{-12345.6}");
+        test(String.format("%, -10G", 0.0), fmt."%, -10G\{0.0}");
+        test(String.format("%, -10G", 12345.6), fmt."%, -10G\{12345.6}");
+
+        test(String.format("%g", -12345.6), fmt."%g\{-12345.6}");
+        test(String.format("%g", 0.0), fmt."%g\{0.0}");
+        test(String.format("%g", 12345.6), fmt."%g\{12345.6}");
+        test(String.format("%10g", -12345.6), fmt."%10g\{-12345.6}");
+        test(String.format("%10g", 0.0), fmt."%10g\{0.0}");
+        test(String.format("%10g", 12345.6), fmt."%10g\{12345.6}");
+        test(String.format("%-10g", -12345.6), fmt."%-10g\{-12345.6}");
+        test(String.format("%-10g", 0.0), fmt."%-10g\{0.0}");
+        test(String.format("%-10g", 12345.6), fmt."%-10g\{12345.6}");
+        test(String.format("%G", -12345.6), fmt."%G\{-12345.6}");
+        test(String.format("%G", 0.0), fmt."%G\{0.0}");
+        test(String.format("%G", 12345.6), fmt."%G\{12345.6}");
+        test(String.format("%10G", -12345.6), fmt."%10G\{-12345.6}");
+        test(String.format("%10G", 0.0), fmt."%10G\{0.0}");
+        test(String.format("%10G", 12345.6), fmt."%10G\{12345.6}");
+        test(String.format("%-10G", -12345.6), fmt."%-10G\{-12345.6}");
+        test(String.format("%-10G", 0.0), fmt."%-10G\{0.0}");
+        test(String.format("%-10G", 12345.6), fmt."%-10G\{12345.6}");
+        test(String.format("%,g", -12345.6), fmt."%,g\{-12345.6}");
+        test(String.format("%,g", 0.0), fmt."%,g\{0.0}");
+        test(String.format("%,g", 12345.6), fmt."%,g\{12345.6}");
+        test(String.format("%,10g", -12345.6), fmt."%,10g\{-12345.6}");
+        test(String.format("%,10g", 0.0), fmt."%,10g\{0.0}");
+        test(String.format("%,10g", 12345.6), fmt."%,10g\{12345.6}");
+        test(String.format("%,-10g", -12345.6), fmt."%,-10g\{-12345.6}");
+        test(String.format("%,-10g", 0.0), fmt."%,-10g\{0.0}");
+        test(String.format("%,-10g", 12345.6), fmt."%,-10g\{12345.6}");
+        test(String.format("%,G", -12345.6), fmt."%,G\{-12345.6}");
+        test(String.format("%,G", 0.0), fmt."%,G\{0.0}");
+        test(String.format("%,G", 12345.6), fmt."%,G\{12345.6}");
+        test(String.format("%,10G", -12345.6), fmt."%,10G\{-12345.6}");
+        test(String.format("%,10G", 0.0), fmt."%,10G\{0.0}");
+        test(String.format("%,10G", 12345.6), fmt."%,10G\{12345.6}");
+        test(String.format("%,-10G", -12345.6), fmt."%,-10G\{-12345.6}");
+        test(String.format("%,-10G", 0.0), fmt."%,-10G\{0.0}");
+        test(String.format("%,-10G", 12345.6), fmt."%,-10G\{12345.6}");
+        test(String.format("%+g", -12345.6), fmt."%+g\{-12345.6}");
+        test(String.format("%+g", 0.0), fmt."%+g\{0.0}");
+        test(String.format("%+g", 12345.6), fmt."%+g\{12345.6}");
+        test(String.format("%+10g", -12345.6), fmt."%+10g\{-12345.6}");
+        test(String.format("%+10g", 0.0), fmt."%+10g\{0.0}");
+        test(String.format("%+10g", 12345.6), fmt."%+10g\{12345.6}");
+        test(String.format("%+-10g", -12345.6), fmt."%+-10g\{-12345.6}");
+        test(String.format("%+-10g", 0.0), fmt."%+-10g\{0.0}");
+        test(String.format("%+-10g", 12345.6), fmt."%+-10g\{12345.6}");
+        test(String.format("%+G", -12345.6), fmt."%+G\{-12345.6}");
+        test(String.format("%+G", 0.0), fmt."%+G\{0.0}");
+        test(String.format("%+G", 12345.6), fmt."%+G\{12345.6}");
+        test(String.format("%+10G", -12345.6), fmt."%+10G\{-12345.6}");
+        test(String.format("%+10G", 0.0), fmt."%+10G\{0.0}");
+        test(String.format("%+10G", 12345.6), fmt."%+10G\{12345.6}");
+        test(String.format("%+-10G", -12345.6), fmt."%+-10G\{-12345.6}");
+        test(String.format("%+-10G", 0.0), fmt."%+-10G\{0.0}");
+        test(String.format("%+-10G", 12345.6), fmt."%+-10G\{12345.6}");
+        test(String.format("%,+g", -12345.6), fmt."%,+g\{-12345.6}");
+        test(String.format("%,+g", 0.0), fmt."%,+g\{0.0}");
+        test(String.format("%,+g", 12345.6), fmt."%,+g\{12345.6}");
+        test(String.format("%,+10g", -12345.6), fmt."%,+10g\{-12345.6}");
+        test(String.format("%,+10g", 0.0), fmt."%,+10g\{0.0}");
+        test(String.format("%,+10g", 12345.6), fmt."%,+10g\{12345.6}");
+        test(String.format("%,+-10g", -12345.6), fmt."%,+-10g\{-12345.6}");
+        test(String.format("%,+-10g", 0.0), fmt."%,+-10g\{0.0}");
+        test(String.format("%,+-10g", 12345.6), fmt."%,+-10g\{12345.6}");
+        test(String.format("%,+G", -12345.6), fmt."%,+G\{-12345.6}");
+        test(String.format("%,+G", 0.0), fmt."%,+G\{0.0}");
+        test(String.format("%,+G", 12345.6), fmt."%,+G\{12345.6}");
+        test(String.format("%,+10G", -12345.6), fmt."%,+10G\{-12345.6}");
+        test(String.format("%,+10G", 0.0), fmt."%,+10G\{0.0}");
+        test(String.format("%,+10G", 12345.6), fmt."%,+10G\{12345.6}");
+        test(String.format("%,+-10G", -12345.6), fmt."%,+-10G\{-12345.6}");
+        test(String.format("%,+-10G", 0.0), fmt."%,+-10G\{0.0}");
+        test(String.format("%,+-10G", 12345.6), fmt."%,+-10G\{12345.6}");
+
+        test(String.format("%g", -12345.6), fmt."%g\{-12345.6}");
+        test(String.format("%g", 0.0), fmt."%g\{0.0}");
+        test(String.format("%g", 12345.6), fmt."%g\{12345.6}");
+        test(String.format("%10g", -12345.6), fmt."%10g\{-12345.6}");
+        test(String.format("%10g", 0.0), fmt."%10g\{0.0}");
+        test(String.format("%10g", 12345.6), fmt."%10g\{12345.6}");
+        test(String.format("%-10g", -12345.6), fmt."%-10g\{-12345.6}");
+        test(String.format("%-10g", 0.0), fmt."%-10g\{0.0}");
+        test(String.format("%-10g", 12345.6), fmt."%-10g\{12345.6}");
+        test(String.format("%G", -12345.6), fmt."%G\{-12345.6}");
+        test(String.format("%G", 0.0), fmt."%G\{0.0}");
+        test(String.format("%G", 12345.6), fmt."%G\{12345.6}");
+        test(String.format("%10G", -12345.6), fmt."%10G\{-12345.6}");
+        test(String.format("%10G", 0.0), fmt."%10G\{0.0}");
+        test(String.format("%10G", 12345.6), fmt."%10G\{12345.6}");
+        test(String.format("%-10G", -12345.6), fmt."%-10G\{-12345.6}");
+        test(String.format("%-10G", 0.0), fmt."%-10G\{0.0}");
+        test(String.format("%-10G", 12345.6), fmt."%-10G\{12345.6}");
+        test(String.format("%,g", -12345.6), fmt."%,g\{-12345.6}");
+        test(String.format("%,g", 0.0), fmt."%,g\{0.0}");
+        test(String.format("%,g", 12345.6), fmt."%,g\{12345.6}");
+        test(String.format("%,10g", -12345.6), fmt."%,10g\{-12345.6}");
+        test(String.format("%,10g", 0.0), fmt."%,10g\{0.0}");
+        test(String.format("%,10g", 12345.6), fmt."%,10g\{12345.6}");
+        test(String.format("%,-10g", -12345.6), fmt."%,-10g\{-12345.6}");
+        test(String.format("%,-10g", 0.0), fmt."%,-10g\{0.0}");
+        test(String.format("%,-10g", 12345.6), fmt."%,-10g\{12345.6}");
+        test(String.format("%,G", -12345.6), fmt."%,G\{-12345.6}");
+        test(String.format("%,G", 0.0), fmt."%,G\{0.0}");
+        test(String.format("%,G", 12345.6), fmt."%,G\{12345.6}");
+        test(String.format("%,10G", -12345.6), fmt."%,10G\{-12345.6}");
+        test(String.format("%,10G", 0.0), fmt."%,10G\{0.0}");
+        test(String.format("%,10G", 12345.6), fmt."%,10G\{12345.6}");
+        test(String.format("%,-10G", -12345.6), fmt."%,-10G\{-12345.6}");
+        test(String.format("%,-10G", 0.0), fmt."%,-10G\{0.0}");
+        test(String.format("%,-10G", 12345.6), fmt."%,-10G\{12345.6}");
+        test(String.format("%(g", -12345.6), fmt."%(g\{-12345.6}");
+        test(String.format("%(g", 0.0), fmt."%(g\{0.0}");
+        test(String.format("%(g", 12345.6), fmt."%(g\{12345.6}");
+        test(String.format("%(10g", -12345.6), fmt."%(10g\{-12345.6}");
+        test(String.format("%(10g", 0.0), fmt."%(10g\{0.0}");
+        test(String.format("%(10g", 12345.6), fmt."%(10g\{12345.6}");
+        test(String.format("%(-10g", -12345.6), fmt."%(-10g\{-12345.6}");
+        test(String.format("%(-10g", 0.0), fmt."%(-10g\{0.0}");
+        test(String.format("%(-10g", 12345.6), fmt."%(-10g\{12345.6}");
+        test(String.format("%(G", -12345.6), fmt."%(G\{-12345.6}");
+        test(String.format("%(G", 0.0), fmt."%(G\{0.0}");
+        test(String.format("%(G", 12345.6), fmt."%(G\{12345.6}");
+        test(String.format("%(10G", -12345.6), fmt."%(10G\{-12345.6}");
+        test(String.format("%(10G", 0.0), fmt."%(10G\{0.0}");
+        test(String.format("%(10G", 12345.6), fmt."%(10G\{12345.6}");
+        test(String.format("%(-10G", -12345.6), fmt."%(-10G\{-12345.6}");
+        test(String.format("%(-10G", 0.0), fmt."%(-10G\{0.0}");
+        test(String.format("%(-10G", 12345.6), fmt."%(-10G\{12345.6}");
+        test(String.format("%,(g", -12345.6), fmt."%,(g\{-12345.6}");
+        test(String.format("%,(g", 0.0), fmt."%,(g\{0.0}");
+        test(String.format("%,(g", 12345.6), fmt."%,(g\{12345.6}");
+        test(String.format("%,(10g", -12345.6), fmt."%,(10g\{-12345.6}");
+        test(String.format("%,(10g", 0.0), fmt."%,(10g\{0.0}");
+        test(String.format("%,(10g", 12345.6), fmt."%,(10g\{12345.6}");
+        test(String.format("%,(-10g", -12345.6), fmt."%,(-10g\{-12345.6}");
+        test(String.format("%,(-10g", 0.0), fmt."%,(-10g\{0.0}");
+        test(String.format("%,(-10g", 12345.6), fmt."%,(-10g\{12345.6}");
+        test(String.format("%,(G", -12345.6), fmt."%,(G\{-12345.6}");
+        test(String.format("%,(G", 0.0), fmt."%,(G\{0.0}");
+        test(String.format("%,(G", 12345.6), fmt."%,(G\{12345.6}");
+        test(String.format("%,(10G", -12345.6), fmt."%,(10G\{-12345.6}");
+        test(String.format("%,(10G", 0.0), fmt."%,(10G\{0.0}");
+        test(String.format("%,(10G", 12345.6), fmt."%,(10G\{12345.6}");
+        test(String.format("%,(-10G", -12345.6), fmt."%,(-10G\{-12345.6}");
+        test(String.format("%,(-10G", 0.0), fmt."%,(-10G\{0.0}");
+        test(String.format("%,(-10G", 12345.6), fmt."%,(-10G\{12345.6}");
+        test(String.format("%+g", -12345.6), fmt."%+g\{-12345.6}");
+        test(String.format("%+g", 0.0), fmt."%+g\{0.0}");
+        test(String.format("%+g", 12345.6), fmt."%+g\{12345.6}");
+        test(String.format("%+10g", -12345.6), fmt."%+10g\{-12345.6}");
+        test(String.format("%+10g", 0.0), fmt."%+10g\{0.0}");
+        test(String.format("%+10g", 12345.6), fmt."%+10g\{12345.6}");
+        test(String.format("%+-10g", -12345.6), fmt."%+-10g\{-12345.6}");
+        test(String.format("%+-10g", 0.0), fmt."%+-10g\{0.0}");
+        test(String.format("%+-10g", 12345.6), fmt."%+-10g\{12345.6}");
+        test(String.format("%+G", -12345.6), fmt."%+G\{-12345.6}");
+        test(String.format("%+G", 0.0), fmt."%+G\{0.0}");
+        test(String.format("%+G", 12345.6), fmt."%+G\{12345.6}");
+        test(String.format("%+10G", -12345.6), fmt."%+10G\{-12345.6}");
+        test(String.format("%+10G", 0.0), fmt."%+10G\{0.0}");
+        test(String.format("%+10G", 12345.6), fmt."%+10G\{12345.6}");
+        test(String.format("%+-10G", -12345.6), fmt."%+-10G\{-12345.6}");
+        test(String.format("%+-10G", 0.0), fmt."%+-10G\{0.0}");
+        test(String.format("%+-10G", 12345.6), fmt."%+-10G\{12345.6}");
+        test(String.format("%,+g", -12345.6), fmt."%,+g\{-12345.6}");
+        test(String.format("%,+g", 0.0), fmt."%,+g\{0.0}");
+        test(String.format("%,+g", 12345.6), fmt."%,+g\{12345.6}");
+        test(String.format("%,+10g", -12345.6), fmt."%,+10g\{-12345.6}");
+        test(String.format("%,+10g", 0.0), fmt."%,+10g\{0.0}");
+        test(String.format("%,+10g", 12345.6), fmt."%,+10g\{12345.6}");
+        test(String.format("%,+-10g", -12345.6), fmt."%,+-10g\{-12345.6}");
+        test(String.format("%,+-10g", 0.0), fmt."%,+-10g\{0.0}");
+        test(String.format("%,+-10g", 12345.6), fmt."%,+-10g\{12345.6}");
+        test(String.format("%,+G", -12345.6), fmt."%,+G\{-12345.6}");
+        test(String.format("%,+G", 0.0), fmt."%,+G\{0.0}");
+        test(String.format("%,+G", 12345.6), fmt."%,+G\{12345.6}");
+        test(String.format("%,+10G", -12345.6), fmt."%,+10G\{-12345.6}");
+        test(String.format("%,+10G", 0.0), fmt."%,+10G\{0.0}");
+        test(String.format("%,+10G", 12345.6), fmt."%,+10G\{12345.6}");
+        test(String.format("%,+-10G", -12345.6), fmt."%,+-10G\{-12345.6}");
+        test(String.format("%,+-10G", 0.0), fmt."%,+-10G\{0.0}");
+        test(String.format("%,+-10G", 12345.6), fmt."%,+-10G\{12345.6}");
+        test(String.format("%(+g", -12345.6), fmt."%(+g\{-12345.6}");
+        test(String.format("%(+g", 0.0), fmt."%(+g\{0.0}");
+        test(String.format("%(+g", 12345.6), fmt."%(+g\{12345.6}");
+        test(String.format("%(+10g", -12345.6), fmt."%(+10g\{-12345.6}");
+        test(String.format("%(+10g", 0.0), fmt."%(+10g\{0.0}");
+        test(String.format("%(+10g", 12345.6), fmt."%(+10g\{12345.6}");
+        test(String.format("%(+-10g", -12345.6), fmt."%(+-10g\{-12345.6}");
+        test(String.format("%(+-10g", 0.0), fmt."%(+-10g\{0.0}");
+        test(String.format("%(+-10g", 12345.6), fmt."%(+-10g\{12345.6}");
+        test(String.format("%(+G", -12345.6), fmt."%(+G\{-12345.6}");
+        test(String.format("%(+G", 0.0), fmt."%(+G\{0.0}");
+        test(String.format("%(+G", 12345.6), fmt."%(+G\{12345.6}");
+        test(String.format("%(+10G", -12345.6), fmt."%(+10G\{-12345.6}");
+        test(String.format("%(+10G", 0.0), fmt."%(+10G\{0.0}");
+        test(String.format("%(+10G", 12345.6), fmt."%(+10G\{12345.6}");
+        test(String.format("%(+-10G", -12345.6), fmt."%(+-10G\{-12345.6}");
+        test(String.format("%(+-10G", 0.0), fmt."%(+-10G\{0.0}");
+        test(String.format("%(+-10G", 12345.6), fmt."%(+-10G\{12345.6}");
+        test(String.format("%,(+g", -12345.6), fmt."%,(+g\{-12345.6}");
+        test(String.format("%,(+g", 0.0), fmt."%,(+g\{0.0}");
+        test(String.format("%,(+g", 12345.6), fmt."%,(+g\{12345.6}");
+        test(String.format("%,(+10g", -12345.6), fmt."%,(+10g\{-12345.6}");
+        test(String.format("%,(+10g", 0.0), fmt."%,(+10g\{0.0}");
+        test(String.format("%,(+10g", 12345.6), fmt."%,(+10g\{12345.6}");
+        test(String.format("%,(+-10g", -12345.6), fmt."%,(+-10g\{-12345.6}");
+        test(String.format("%,(+-10g", 0.0), fmt."%,(+-10g\{0.0}");
+        test(String.format("%,(+-10g", 12345.6), fmt."%,(+-10g\{12345.6}");
+        test(String.format("%,(+G", -12345.6), fmt."%,(+G\{-12345.6}");
+        test(String.format("%,(+G", 0.0), fmt."%,(+G\{0.0}");
+        test(String.format("%,(+G", 12345.6), fmt."%,(+G\{12345.6}");
+        test(String.format("%,(+10G", -12345.6), fmt."%,(+10G\{-12345.6}");
+        test(String.format("%,(+10G", 0.0), fmt."%,(+10G\{0.0}");
+        test(String.format("%,(+10G", 12345.6), fmt."%,(+10G\{12345.6}");
+        test(String.format("%,(+-10G", -12345.6), fmt."%,(+-10G\{-12345.6}");
+        test(String.format("%,(+-10G", 0.0), fmt."%,(+-10G\{0.0}");
+        test(String.format("%,(+-10G", 12345.6), fmt."%,(+-10G\{12345.6}");
+
+        test(String.format("%a", -12345.6), fmt."%a\{-12345.6}");
+        test(String.format("%a", 0.0), fmt."%a\{0.0}");
+        test(String.format("%a", 12345.6), fmt."%a\{12345.6}");
+        test(String.format("%10a", -12345.6), fmt."%10a\{-12345.6}");
+        test(String.format("%10a", 0.0), fmt."%10a\{0.0}");
+        test(String.format("%10a", 12345.6), fmt."%10a\{12345.6}");
+        test(String.format("%-10a", -12345.6), fmt."%-10a\{-12345.6}");
+        test(String.format("%-10a", 0.0), fmt."%-10a\{0.0}");
+        test(String.format("%-10a", 12345.6), fmt."%-10a\{12345.6}");
+        test(String.format("%A", -12345.6), fmt."%A\{-12345.6}");
+        test(String.format("%A", 0.0), fmt."%A\{0.0}");
+        test(String.format("%A", 12345.6), fmt."%A\{12345.6}");
+        test(String.format("%10A", -12345.6), fmt."%10A\{-12345.6}");
+        test(String.format("%10A", 0.0), fmt."%10A\{0.0}");
+        test(String.format("%10A", 12345.6), fmt."%10A\{12345.6}");
+        test(String.format("%-10A", -12345.6), fmt."%-10A\{-12345.6}");
+        test(String.format("%-10A", 0.0), fmt."%-10A\{0.0}");
+        test(String.format("%-10A", 12345.6), fmt."%-10A\{12345.6}");
+    }
+}

test/jdk/java/lang/template/StringTemplateTest.java

@@ -0,0 +1,308 @@
+/*
+ * Copyright (c) 2023, Oracle and/or its affiliates. All rights reserved.
+ * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
+ *
+ * This code is free software; you can redistribute it and/or modify it
+ * under the terms of the GNU General Public License version 2 only, as
+ * published by the Free Software Foundation.
+ *
+ * This code is distributed in the hope that it will be useful, but WITHOUT
+ * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
+ * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
+ * version 2 for more details (a copy is included in the LICENSE file that
+ * accompanied this code).
+ *
+ * You should have received a copy of the GNU General Public License version
+ * 2 along with this work; if not, write to the Free Software Foundation,
+ * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
+ *
+ * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
+ * or visit www.oracle.com if you need additional information or have any
+ * questions.
+ */
+
+/*
+ * @test
+ * @bug 0000000
+ * @summary Exercise runtime handing of templated strings.
+ * @enablePreview true
+ */
+
+import java.io.ByteArrayOutputStream;
+import java.io.FilterOutputStream;
+import java.io.IOException;
+import java.io.OutputStream;
+import java.net.URI;
+import java.util.*;
+import java.util.function.Supplier;
+import javax.tools.FileObject;
+import javax.tools.ForwardingJavaFileManager;
+import javax.tools.JavaFileManager;
+import javax.tools.JavaFileObject;
+import javax.tools.SimpleJavaFileObject;
+import static javax.tools.StandardLocation.CLASS_OUTPUT;
+import javax.tools.ToolProvider;
+
+public class StringTemplateTest {
+    enum Category{GENERAL, CHARACTER, INTEGRAL, BIG_INT, FLOATING, BIG_FLOAT, DATE};
+
+    static final String[] GENERAL = {"true", "false", "(Object)null", "STR", "BO", "BOOL", "(Boolean)null"};
+    static final String[] CHARS = {"C", "CHAR", "(Character)null"};
+    static final String[] INTS = {"L", "LONG", "I", "INT", "S", "SHORT", "BY", "BYTE", "Long.MAX_VALUE", "Long.MIN_VALUE", "(Long)null", "(Integer)null", "(Short)null", "(Byte)null"};
+    static final String[] BIGINTS = {};
+    static final String[] FLOATS = {"F", "FLOAT", "D", "DOUBLE", "Double.NEGATIVE_INFINITY", "Double.NaN", "Double.MAX_VALUE", "(Double)null", "(Float)null"};
+    static final String[] BIGFLOATS = {};
+    static final String[] DATES = {};
+
+    final Random r = new Random(1);
+
+    String randomValue(Category category) {
+        return switch (category) {
+            case GENERAL -> randomChoice(
+                    GENERAL,
+                    () -> randomValue(Category.CHARACTER),
+                    () -> randomValue(Category.INTEGRAL),
+                    () -> randomValue(Category.BIG_INT),
+                    () -> randomValue(Category.FLOATING),
+                    () -> randomValue(Category.BIG_FLOAT),
+                    () -> randomValue(Category.DATE),
+                    () -> "\"" + randomString(r.nextInt(10)) + "\"");
+            case CHARACTER -> randomChoice(
+                    CHARS,
+                    () -> "\'" + randomString(1) + "\'");
+            case INTEGRAL -> randomChoice(
+                    INTS,
+                    () -> "(byte)" + String.valueOf(r.nextInt(Byte.MIN_VALUE, Byte.MAX_VALUE)),
+                    () -> "(short)" + String.valueOf(r.nextInt(Short.MIN_VALUE, Short.MAX_VALUE)),
+                    () -> String.valueOf(r.nextInt()),
+                    () -> r.nextLong() + "l");
+            case BIG_INT -> randomChoice(
+                    BIGINTS,
+                    () -> "new java.math.BigInteger(\"" + r.nextLong() + "\")");
+            case FLOATING -> randomChoice(
+                    FLOATS,
+                    () -> String.valueOf(r.nextDouble()),
+                    () -> r.nextFloat() + "f");
+            case BIG_FLOAT -> randomChoice(
+                    BIGFLOATS,
+                    () -> "new java.math.BigDecimal(" + r.nextDouble() + ")");
+            case DATE -> randomChoice(
+                    DATES,
+                    () -> "new java.util.Date(" + r.nextLong() + "l)",
+                    () -> r.nextLong() + "l");
+        };
+    }
+
+    String randomChoice(Supplier<String>... suppl) {
+        return suppl[r.nextInt(suppl.length)].get();
+    }
+
+    String randomChoice(String... values) {
+        return values[r.nextInt(values.length)];
+    }
+
+    String randomChoice(String[] values, Supplier<String>... suppl) {
+        int i = r.nextInt(values.length + suppl.length);
+        return i < values.length ? values[i] : suppl[i - values.length].get();
+    }
+
+    String randomString(int length) {
+        var sb = new StringBuilder(length << 2);
+        while (length-- > 0) {
+            char ch = (char)r.nextInt(9, 128);
+            var s = switch (ch) {
+                case '\t' -> "\\t";
+                case '\'' -> "\\\'";
+                case '"' -> "\\\"";
+                case '\r' -> "\\r";
+                case '\\' -> "\\\\";
+                case '\n' -> "\\n";
+                case '\f' -> "\\f";
+                case '\b' -> "\\b";
+                default -> ch + "";
+            };
+            sb.append(s);
+        }
+        return sb.toString();
+    }
+
+    String randomFormat(Category category) {
+        char c;
+        return "%" + switch (category) {
+            case GENERAL -> randomWidth("-") + randomPrecision() + randomChar("bBhHsS");
+            case CHARACTER -> randomWidth("-") + randomChar("cC");
+            case INTEGRAL -> switch (c = randomChar("doxX")) {
+                case 'd' -> randomFlags("+ ,(");
+                default -> randomFlags("");
+            } + randomWidth("-0") + c;
+            case BIG_INT -> switch (c = randomChar("doxX")) {
+                case 'd' -> randomFlags("+ ,(");
+                default -> randomFlags("+ (");
+            } + randomWidth("-0") + c;
+            case FLOATING -> switch (c = randomChar("eEfaAgG")) {
+                case 'a', 'A' -> randomFlags("+ ") + randomWidth("-0");
+                case 'e', 'E' -> randomFlags("+ (") + randomWidth("-0") + randomPrecision();
+                default -> randomFlags("+ ,(") + randomWidth("-0") + randomPrecision();
+            } + c;
+            case BIG_FLOAT -> switch (c = randomChar("eEfgG")) {
+                case 'e', 'E' -> randomFlags("+ (") + randomWidth("-0") + randomPrecision();
+                default -> randomFlags("+ ,(") + randomWidth("-0") + randomPrecision();
+            } + c;
+            case DATE ->  randomWidth("-") + randomChar("tT") + randomChar("BbhAaCYyjmdeRTrDFc");
+        };
+    }
+
+    String randomFlags(String flags) {
+        var sb = new StringBuilder(flags.length());
+        for (var f : flags.toCharArray()) {
+            if (r.nextBoolean() && (f != ' ' || sb.length() == 0 || sb.charAt(sb.length() - 1) != '+')) sb.append(f);
+        }
+        return sb.toString();
+    }
+
+    char randomChar(String chars) {
+        return chars.charAt(r.nextInt(chars.length()));
+    }
+
+    String randomWidth(String flags) {
+        var f = r.nextInt(flags.length() + 1);
+        return r.nextBoolean() ? (r.nextBoolean() ? flags.charAt(r.nextInt(flags.length())) : "") + String.valueOf(r.nextInt(10) + 1) : "";
+    }
+
+    String randomPrecision() {
+        return r.nextBoolean() ? '.' + String.valueOf(r.nextInt(10) + 1) : "";
+    }
+
+    public Class<?> compile() throws Exception {
+        var classes = new HashMap<String, byte[]>();
+        var fileManager = new ForwardingJavaFileManager(ToolProvider.getSystemJavaCompiler().getStandardFileManager(null, null, null)) {
+            @Override
+            public ClassLoader getClassLoader(JavaFileManager.Location location) {
+                return new ClassLoader() {
+                    @Override
+                    public Class<?> loadClass(String name) throws ClassNotFoundException {
+                        try {
+                            return super.loadClass(name);
+                        } catch (ClassNotFoundException e) {
+                            byte[] classData = classes.get(name);
+                            return defineClass(name, classData, 0, classData.length);
+                        }
+                    }
+                };
+            }
+            @Override
+            public JavaFileObject getJavaFileForOutput(JavaFileManager.Location location, String name, JavaFileObject.Kind kind, FileObject originatingSource) throws UnsupportedOperationException {
+                return new SimpleJavaFileObject(URI.create(name + ".class"), JavaFileObject.Kind.CLASS) {
+                    @Override
+                    public OutputStream openOutputStream() {
+                        return new FilterOutputStream(new ByteArrayOutputStream()) {
+                            @Override
+                            public void close() throws IOException {
+                                classes.put(name, ((ByteArrayOutputStream)out).toByteArray());
+                            }
+                        };
+                    }
+                };
+            }
+        };
+        var source = genSource();
+//        System.out.println(source);
+        if (ToolProvider.getSystemJavaCompiler().getTask(null, fileManager, null,
+                List.of("--enable-preview", "-source", String.valueOf(Runtime.version().feature())), null,
+                List.of(new SimpleJavaFileObject(URI.create("StringTemplateTest$.java"), JavaFileObject.Kind.SOURCE) {
+            @Override
+            public CharSequence getCharContent(boolean ignoreEncodingErrors) {
+                return source;
+            }
+        })).call()) {
+            return fileManager.getClassLoader(CLASS_OUTPUT).loadClass("StringTemplateTest$");
+        } else {
+            throw new AssertionError("compilation failed");
+        }
+    }
+
+    String genFragments(Category c) {
+        var fragments = new LinkedList<String>();
+        for (int i = 0; i < 1500; i++) {
+            var format = randomFormat(c);
+            var value = randomValue(c);
+            var qValue = value.replace("\\", "\\\\").replace("\"", "\\\"");
+            fragments.add(STR."test(FMT.\"\{format}\\{\{value}}\", \"\{format}\", \"\{qValue}\", \{value}, log);");
+        }
+        return String.join("\n        ", fragments);
+    }
+
+    String genSource() {
+        return STR."""
+            import java.util.FormatProcessor;
+            import java.util.Locale;
+
+            public class StringTemplateTest$ {
+                static final FormatProcessor FMT = FormatProcessor.create(Locale.US);
+                static String STR = "this is static String";
+                static char C = 'c';
+                static Character CHAR = 'C';
+                static long L = -12345678910l;
+                static Long LONG = 9876543210l;
+                static int I = 42;
+                static Integer INT = -49;
+                static boolean BO = true;
+                static Boolean BOOL = false;
+                static short S = 13;
+                static Short SHORT = -17;
+                static byte BY = -3;
+                static Byte BYTE = 12;
+                static float F = 4.789f;
+                static Float FLOAT = -0.000006f;
+                static double D = 6545745.6734654563;
+                static Double DOUBLE = -4323.7645676574;
+
+                public static void run(java.util.List<String> log) {
+                    runGeneral(log);
+                    runCharacter(log);
+                    runIntegral(log);
+                    runBigInt(log);
+                    runFloating(log);
+                    runBigFloat(log);
+                    runDate(log);
+                }
+                public static void runGeneral(java.util.List<String> log) {
+                    \{genFragments(Category.GENERAL)}
+                }
+                public static void runCharacter(java.util.List<String> log) {
+                    \{genFragments(Category.CHARACTER)}
+                }
+                public static void runIntegral(java.util.List<String> log) {
+                    \{genFragments(Category.INTEGRAL)}
+                }
+                public static void runBigInt(java.util.List<String> log) {
+                    \{genFragments(Category.BIG_INT)}
+                }
+                public static void runFloating(java.util.List<String> log) {
+                    \{genFragments(Category.FLOATING)}
+                }
+                public static void runBigFloat(java.util.List<String> log) {
+                    \{genFragments(Category.BIG_FLOAT)}
+                }
+                public static void runDate(java.util.List<String> log) {
+                    \{genFragments(Category.DATE)}
+                }
+                static void test(String fmt, String format, String expression, Object value, java.util.List<String> log) {
+                    var formatted = String.format(java.util.Locale.US, format, value);
+                    if (!fmt.equals(formatted)) {
+                        log.add("  format: '%s' expression: '%s' value: '%s' expected: '%s' found: '%s'".formatted(format, expression, value, formatted, fmt));
+                    }
+                }
+            }
+            """;
+    }
+
+    public static void main(String... args) throws Exception {
+        var log = new LinkedList<String>();
+        new StringTemplateTest().compile().getMethod("run", List.class).invoke(null, log);
+        if (!log.isEmpty()) {
+            log.forEach(System.out::println);
+            throw new AssertionError(STR."failed \{log.size()} tests");
+        }
+    }
+}

test/langtools/jdk/jshell/CompletenessTest.java

@@ -89,7 +89,8 @@ public class CompletenessTest extends KullaTesting {
         "record.any",
         "record()",
         "record(1)",
-        "record.length()"
+        "record.length()",
+        "\"\\{0}\""
     };
 
     static final String[] complete_with_semi = new String[] {
@@ -232,7 +233,12 @@ public class CompletenessTest extends KullaTesting {
     };
 
     static final String[] unknown = new String[] {
-        "new ;"
+        "new ;",
+        "\"",
+        "\"\\",
+        "\"\\{",
+        "\"\\{0",
+        "\"\\{0}",
     };
 
     static final Map<Completeness, String[]> statusToCases = new HashMap<>();
@@ -369,6 +375,7 @@ public class CompletenessTest extends KullaTesting {
     public void testTextBlocks() {
         assertStatus("\"\"\"", DEFINITELY_INCOMPLETE, null);
         assertStatus("\"\"\"broken", DEFINITELY_INCOMPLETE, null);
+        assertStatus("\"\"\"\n", DEFINITELY_INCOMPLETE, null);
         assertStatus("\"\"\"\ntext", DEFINITELY_INCOMPLETE, null);
         assertStatus("\"\"\"\ntext\"\"", DEFINITELY_INCOMPLETE, "\"\"\"\ntext\"\"\"");
         assertStatus("\"\"\"\ntext\"\"\"", COMPLETE, "\"\"\"\ntext\"\"\"");
@@ -376,6 +383,10 @@ public class CompletenessTest extends KullaTesting {
         assertStatus("\"\"\"\ntext\\\"\"\"", DEFINITELY_INCOMPLETE, null);
         assertStatus("\"\"\"\ntext\\\"\"\"\\\"\"\"", DEFINITELY_INCOMPLETE, null);
         assertStatus("\"\"\"\ntext\\\"\"\"\\\"\"\"\"\"\"", COMPLETE, "\"\"\"\ntext\\\"\"\"\\\"\"\"\"\"\"");
+        assertStatus("\"\"\"\n\\", DEFINITELY_INCOMPLETE, null);
+        assertStatus("\"\"\"\n\\{", DEFINITELY_INCOMPLETE, null);
+        assertStatus("\"\"\"\n\\{0", DEFINITELY_INCOMPLETE, null);
+        assertStatus("\"\"\"\n\\{0}", DEFINITELY_INCOMPLETE, null);
     }
 
     public void testMiscSource() {

test/langtools/tools/javac/api/TestJavacTaskScanner.java

@@ -103,7 +103,7 @@ public class TestJavacTaskScanner extends ToolTester {
 
         check(numTokens, "#Tokens", 1054);
         check(numParseTypeElements, "#parseTypeElements", 180);
-        check(numAllMembers, "#allMembers", 52);
+        check(numAllMembers, "#allMembers", 64);
     }
 
     void check(int value, String name, int expected) {

test/langtools/tools/javac/diags/examples/StringTemplate.java

@@ -0,0 +1,33 @@
+/*
+ * Copyright (c) 2023, Oracle and/or its affiliates. All rights reserved.
+ * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
+ *
+ * This code is free software; you can redistribute it and/or modify it
+ * under the terms of the GNU General Public License version 2 only, as
+ * published by the Free Software Foundation.
+ *
+ * This code is distributed in the hope that it will be useful, but WITHOUT
+ * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
+ * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
+ * version 2 for more details (a copy is included in the LICENSE file that
+ * accompanied this code).
+ *
+ * You should have received a copy of the GNU General Public License version
+ * 2 along with this work; if not, write to the Free Software Foundation,
+ * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
+ *
+ * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
+ * or visit www.oracle.com if you need additional information or have any
+ * questions.
+ */
+
+ // key: compiler.misc.feature.string.templates
+ // key: compiler.warn.preview.feature.use.plural
+ // options: --enable-preview -source 21  -Xlint:preview
+
+class StringTemplate {
+    String m() {
+        int x = 10, y = 20;
+        return STR."\{x} + \{y} = \{x + y}";
+    }
+}

test/langtools/tools/javac/diags/examples/StringTemplateNoProcessor.java

@@ -0,0 +1,34 @@
+/*
+ * Copyright (c) 2023, Oracle and/or its affiliates. All rights reserved.
+ * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
+ *
+ * This code is free software; you can redistribute it and/or modify it
+ * under the terms of the GNU General Public License version 2 only, as
+ * published by the Free Software Foundation.
+ *
+ * This code is distributed in the hope that it will be useful, but WITHOUT
+ * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
+ * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
+ * version 2 for more details (a copy is included in the LICENSE file that
+ * accompanied this code).
+ *
+ * You should have received a copy of the GNU General Public License version
+ * 2 along with this work; if not, write to the Free Software Foundation,
+ * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
+ *
+ * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
+ * or visit www.oracle.com if you need additional information or have any
+ * questions.
+ */
+
+ // key: compiler.err.processor.missing.from.string.template.expression
+ // key: compiler.misc.feature.string.templates
+ // key: compiler.warn.preview.feature.use.plural
+ // options: --enable-preview -source 21  -Xlint:preview
+
+class StringTemplateNoProcessor {
+    String m() {
+        int x = 10, y = 20;
+        return "\{x} + \{y} = \{x + y}";
+    }
+}

test/langtools/tools/javac/diags/examples/StringTemplateNotProcessor.java

@@ -0,0 +1,37 @@
+/*
+ * Copyright (c) 2023, Oracle and/or its affiliates. All rights reserved.
+ * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
+ *
+ * This code is free software; you can redistribute it and/or modify it
+ * under the terms of the GNU General Public License version 2 only, as
+ * published by the Free Software Foundation.
+ *
+ * This code is distributed in the hope that it will be useful, but WITHOUT
+ * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
+ * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
+ * version 2 for more details (a copy is included in the LICENSE file that
+ * accompanied this code).
+ *
+ * You should have received a copy of the GNU General Public License version
+ * 2 along with this work; if not, write to the Free Software Foundation,
+ * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
+ *
+ * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
+ * or visit www.oracle.com if you need additional information or have any
+ * questions.
+ */
+
+ // key: compiler.note.preview.filename
+ // key: compiler.note.preview.recompile
+ // key: compiler.err.not.a.processor.type
+ // options: --enable-preview  -source 21
+
+import java.lang.*;
+
+class StringTemplateNotProcessor {
+    String m() {
+        String processor = "";
+        int x = 10, y = 20;
+        return processor."\{x} + \{y} = \{x + y}";
+    }
+}

test/langtools/tools/javac/diags/examples/StringTemplateRawProcessor.java

@@ -0,0 +1,45 @@
+/*
+ * Copyright (c) 2023, Oracle and/or its affiliates. All rights reserved.
+ * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
+ *
+ * This code is free software; you can redistribute it and/or modify it
+ * under the terms of the GNU General Public License version 2 only, as
+ * published by the Free Software Foundation.
+ *
+ * This code is distributed in the hope that it will be useful, but WITHOUT
+ * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
+ * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
+ * version 2 for more details (a copy is included in the LICENSE file that
+ * accompanied this code).
+ *
+ * You should have received a copy of the GNU General Public License version
+ * 2 along with this work; if not, write to the Free Software Foundation,
+ * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
+ *
+ * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
+ * or visit www.oracle.com if you need additional information or have any
+ * questions.
+ */
+
+ // key: compiler.note.preview.filename
+ // key: compiler.note.preview.recompile
+ // key: compiler.misc.unexpected.ret.val
+ // key: compiler.err.prob.found.req
+ // key: compiler.err.processor.type.cannot.be.a.raw.type
+ // options: --enable-preview -source 21
+
+import java.lang.*;
+import java.lang.StringTemplate.Processor;
+
+class StringTemplateRawProcessor {
+    void m() {
+        Processor processor = ts -> ts.interpolate();
+        try {
+            int x = 10, y = 20;
+            return processor."\{x} + \{y} = \{x + y}";
+        } catch (Throwable x) {
+            throw new RuntimeException(x);
+        }
+    }
+}
+

test/langtools/tools/javac/diags/examples/StringTemplateUnclosedString.java

@@ -0,0 +1,37 @@
+/*
+ * Copyright (c) 2023, Oracle and/or its affiliates. All rights reserved.
+ * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
+ *
+ * This code is free software; you can redistribute it and/or modify it
+ * under the terms of the GNU General Public License version 2 only, as
+ * published by the Free Software Foundation.
+ *
+ * This code is distributed in the hope that it will be useful, but WITHOUT
+ * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
+ * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
+ * version 2 for more details (a copy is included in the LICENSE file that
+ * accompanied this code).
+ *
+ * You should have received a copy of the GNU General Public License version
+ * 2 along with this work; if not, write to the Free Software Foundation,
+ * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
+ *
+ * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
+ * or visit www.oracle.com if you need additional information or have any
+ * questions.
+ */
+
+ // key: compiler.note.preview.filename
+ // key: compiler.note.preview.recompile
+ // key: compiler.err.unclosed.str.lit
+ // key: compiler.err.string.template.is.not.well.formed
+ // options: --enable-preview -source 21
+
+import java.lang.*;
+
+class StringTemplateUnclosedString {
+    String m() {
+        int x = 10;
+        return STR."\{x";
+    }
+}

test/langtools/tools/javac/diags/examples/StringTemplateUnclosedTextBlock.java

@@ -0,0 +1,42 @@
+/*
+ * Copyright (c) 2023, Oracle and/or its affiliates. All rights reserved.
+ * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
+ *
+ * This code is free software; you can redistribute it and/or modify it
+ * under the terms of the GNU General Public License version 2 only, as
+ * published by the Free Software Foundation.
+ *
+ * This code is distributed in the hope that it will be useful, but WITHOUT
+ * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
+ * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
+ * version 2 for more details (a copy is included in the LICENSE file that
+ * accompanied this code).
+ *
+ * You should have received a copy of the GNU General Public License version
+ * 2 along with this work; if not, write to the Free Software Foundation,
+ * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
+ *
+ * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
+ * or visit www.oracle.com if you need additional information or have any
+ * questions.
+ */
+
+ // key: compiler.note.preview.filename
+ // key: compiler.note.preview.recompile
+ // key: compiler.err.unclosed.text.block
+ // key: compiler.err.text.block.template.is.not.well.formed
+ // key: compiler.err.premature.eof
+ // options: --enable-preview -source 21
+
+import java.lang.*;
+
+class StringTemplateUnclosedTextBlock {
+    String m() {
+        int x = 10;
+        return STR."""
+                aaa
+                \{x
+                """
+        ;
+    }
+}

test/langtools/tools/javac/parser/JavacParserTest.java

@@ -87,6 +87,7 @@ import com.sun.source.tree.DefaultCaseLabelTree;
 import com.sun.source.tree.ModuleTree;
 import com.sun.source.util.TreePathScanner;
 import com.sun.tools.javac.api.JavacTaskPool;
+import com.sun.tools.javac.api.JavacTaskPool.Worker;
 import java.util.Objects;
 
 public class JavacParserTest extends TestCase {
@@ -1912,6 +1913,52 @@ public class JavacParserTest extends TestCase {
         }.scan(cut, null);
     }
 
+    @Test
+    void testStringTemplate1() throws IOException {
+        String code = """
+                      package test;
+                      public class Test {
+                           Test(int a) {
+                               String s = "prefix \\{a} suffix";
+                           }
+                      }
+                      """;
+
+        JavacTaskImpl ct = (JavacTaskImpl) tool.getTask(null, fm, null,
+                null, null, Arrays.asList(new MyFileObject(code)));
+        CompilationUnitTree cut = ct.parse().iterator().next();
+        ClassTree clazz = (ClassTree) cut.getTypeDecls().get(0);
+        MethodTree constr = (MethodTree) clazz.getMembers().get(0);
+        VariableTree decl = (VariableTree) constr.getBody().getStatements().get(0);
+        SourcePositions sp = Trees.instance(ct).getSourcePositions();
+        int initStart = (int) sp.getStartPosition(cut, decl.getInitializer());
+        int initEnd   = (int) sp.getEndPosition(cut, decl.getInitializer());
+        assertEquals("correct templated String span expected", code.substring(initStart, initEnd), "\"prefix \\{a} suffix\"");
+    }
+
+    @Test
+    void testStringTemplate2() throws IOException {
+        String code = """
+                      package test;
+                      public class Test {
+                           Test(int a) {
+                               String s = STR."prefix \\{a} suffix";
+                           }
+                      }
+                      """;
+
+        JavacTaskImpl ct = (JavacTaskImpl) tool.getTask(null, fm, null,
+                null, null, Arrays.asList(new MyFileObject(code)));
+        CompilationUnitTree cut = ct.parse().iterator().next();
+        ClassTree clazz = (ClassTree) cut.getTypeDecls().get(0);
+        MethodTree constr = (MethodTree) clazz.getMembers().get(0);
+        VariableTree decl = (VariableTree) constr.getBody().getStatements().get(0);
+        SourcePositions sp = Trees.instance(ct).getSourcePositions();
+        int initStart = (int) sp.getStartPosition(cut, decl.getInitializer());
+        int initEnd   = (int) sp.getEndPosition(cut, decl.getInitializer());
+        assertEquals("correct templated String span expected", code.substring(initStart, initEnd), "STR.\"prefix \\{a} suffix\"");
+    }
+
     @Test //JDK-8293897
     void testImplicitFinalInTryWithResources() throws IOException {
         String code = """
@@ -1993,6 +2040,63 @@ public class JavacParserTest extends TestCase {
         }.scan(cut, null);
     }
 
+    @Test
+    void testIncompleteStringTemplate() throws IOException {
+        String template = "\"\\{o.toString()}\"";
+        String prefix = """
+                      package t;
+                      class Test {
+                          void test(Object o) {
+                              String s = STR.""";
+
+        Worker<Void> verifyParseable = task -> {
+            try {
+                task.parse().iterator().next();
+                return null;
+            } catch (IOException ex) {
+                throw new AssertionError(ex);
+            }
+        };
+        JavacTaskPool pool = new JavacTaskPool(1);
+        DiagnosticListener<JavaFileObject> dl = d -> {};
+        List<String> options = List.of("--enable-preview",
+                                       "-source", System.getProperty("java.specification.version"));
+        for (int i = 0; i < template.length(); i++) {
+            pool.getTask(null, fm, dl, options,
+                    null, Arrays.asList(new MyFileObject(prefix + template.substring(0, i))),
+                    verifyParseable
+            );
+        }
+        for (int i = 0; i < template.length() - 1; i++) {
+            pool.getTask(null, fm, dl, options,
+                    null, Arrays.asList(new MyFileObject(prefix + template.substring(0, i) + "\"")),
+                    verifyParseable);
+        }
+        String incomplete = prefix + "\"\\{o.";
+        pool.getTask(null, fm, dl, options,
+                null, Arrays.asList(new MyFileObject(incomplete)), task -> {
+            try {
+                CompilationUnitTree cut = task.parse().iterator().next();
+                String result = cut.toString().replaceAll("\\R", "\n");
+                System.out.println("RESULT\n" + result);
+                assertEquals("incorrect AST",
+                             result,
+                             """
+                             package t;
+                             \n\
+                             class Test {
+                                 \n\
+                                 void test(Object o) {
+                                     String s = STR.<error>;
+                                 }
+                             }""");
+                return null;
+            } catch (IOException ex) {
+                throw new AssertionError(ex);
+            }
+        });
+    }
+
     @Test //JDK-8295401
     void testModuleInfoProvidesRecovery() throws IOException {
         String code = """

test/langtools/tools/javac/template/Basic.java

@@ -0,0 +1,240 @@
+/*
+ * Copyright (c) 2023, Oracle and/or its affiliates. All rights reserved.
+ * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
+ *
+ * This code is free software; you can redistribute it and/or modify it
+ * under the terms of the GNU General Public License version 2 only, as
+ * published by the Free Software Foundation.
+ *
+ * This code is distributed in the hope that it will be useful, but WITHOUT
+ * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
+ * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
+ * version 2 for more details (a copy is included in the LICENSE file that
+ * accompanied this code).
+ *
+ * You should have received a copy of the GNU General Public License version
+ * 2 along with this work; if not, write to the Free Software Foundation,
+ * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
+ *
+ * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
+ * or visit www.oracle.com if you need additional information or have any
+ * questions.
+ */
+
+/*
+ * @test
+ * @bug 0000000
+ * @summary Exercise javac handing of templated strings.
+ * @library /tools/lib
+ * @modules jdk.compiler/com.sun.tools.javac.api
+ *          jdk.compiler/com.sun.tools.javac.main
+ * @build toolbox.ToolBox toolbox.JavacTask
+ * @run main Basic
+ */
+
+
+import toolbox.JavacTask;
+import toolbox.JavaTask;
+import toolbox.Task;
+import toolbox.ToolBox;
+
+public class Basic {
+    private static ToolBox TOOLBOX = new ToolBox();
+    private static final String JAVA_VERSION = System.getProperty("java.specification.version");
+
+    public static void main(String... arg) {
+        primitivesTest();
+        missingPartsTest();
+        expressionsTest();
+        invalidExpressionsTest();
+        processorTest();
+    }
+
+    /*
+     * Primitive types test.
+     */
+    static void primitivesTest() {
+        for (String type : new String[] {
+            "byte",
+            "short",
+            "int",
+            "long",
+            "float",
+            "double"
+        }) {
+            compPass(type + " x = 10; " + type + "  y = 20; StringTemplate result = RAW.\"\\{x} + \\{y} = \\{x + y}\";");
+        }
+    }
+
+    /*
+     * Missing parts test.
+     */
+    static void missingPartsTest() {
+        compFail("""
+            int x = 10;
+            StringTemplate result = RAW."\\{x";
+        """);
+        compFail("""
+            int x = 10;
+            StringTemplate result = RAW."\\{{x}";
+        """);
+        compFail("""
+            int x = 10;
+            StringTemplate result = RAW."\\{x + }";
+        """);
+        compFail("""
+            int x = 10;
+            StringTemplate result = RAW."\\{ * x }";
+        """);
+        compFail("""
+            int x = 10;
+            StringTemplate result = RAW."\\{ (x + x }";
+        """);
+    }
+
+    /*
+     * Expressions test.
+     */
+    static void expressionsTest() {
+        compPass("""
+            int x = 10;
+            int[] y = new int[] { 10, 20, 30 };
+            StringTemplate result1 = RAW."\\{x + 1}";
+            StringTemplate result2 = RAW."\\{x + x}";
+            StringTemplate result3 = RAW."\\{x - x}";
+            StringTemplate result4 = RAW."\\{x * x}";
+            StringTemplate result5 = RAW."\\{x / x}";
+            StringTemplate result6 = RAW."\\{x % x}";
+            StringTemplate result7 = RAW."\\{x + (x + x)}";
+            StringTemplate result8 = RAW."\\{y[x - 9]}";
+            StringTemplate result9 = RAW."\\{System.out}";
+            StringTemplate result10 = RAW.\"""
+                    \\{ "a string" }
+                    \""";
+                    """);
+        compPass("""
+            StringTemplate result = RAW.\"""
+                 \\{
+                     new Collection<String>() {
+                          @Override public int size() { return 0; }
+                          @Override public boolean isEmpty() { return false; }
+                          @Override public boolean contains(Object o) { return false; }
+                          @Override public Iterator<String> iterator() { return null; }
+                          @Override public Object[] toArray() { return new Object[0]; }
+                          @Override public <T> T[] toArray(T[] a) { return null; }
+                          @Override public boolean add(String s) { return false; }
+                          @Override public boolean remove(Object o) { return false; }
+                          @Override public boolean containsAll(Collection<?> c) { return false; }
+                          @Override public boolean addAll(Collection<? extends String> c) { return false; }
+                          @Override public boolean removeAll(Collection<?> c) { return false; }
+                          @Override public boolean retainAll(Collection<?> c) { return false; }
+                          @Override public void clear() { }
+                      }
+                 }
+                 \""";
+         """);
+    }
+
+    /*
+     * Invalid expressions test.
+     */
+    static void invalidExpressionsTest() {
+        compFail("""
+            int x = 10;
+            StringTemplate result = RAW."\\{ (x == x }";
+        """);
+        compFail("""
+            int x = 10;
+            StringTemplate result = RAW."\\{ true ?  : x - 1 }";
+        """);
+        compFail("""
+             String result = RAW."\\{ 'a }";
+        """);
+        compFail("""
+            int x = 10;
+            StringTemplate result = RAW."\\{ Math.min(, x - 1) }";
+        """);
+        compFail("""
+            int x = 10;
+            StringTemplate result = RAW."\\{ \\tx }";
+        """);
+    }
+
+    /*
+     * Processor test.
+     */
+    static void processorTest() {
+        compPass("""
+         int x = 10, y = 20;
+         String string = STR."\\{x} + \\{y} = \\{x + y}";
+         """);
+        compFail("""
+         int x = 10, y = 20;
+         String processor = "abc";
+         String string = processor."\\{x} + \\{y} = \\{x + y}";
+         """);
+        compFail("""
+         int x = 10, y = 20;
+         long processor = 100;
+         String string = processor."\\{x} + \\{y} = \\{x + y}";
+         """);
+    }
+
+    /*
+     * Test source for successful compile.
+     */
+    static void compPass(String code) {
+        String source = """
+            import java.lang.*;
+            import java.util.*;
+            import static java.lang.StringTemplate.RAW;
+            public class TEST {
+                public static void main(String... arg) {
+            """ +
+            code.indent(8) +
+            """
+                }
+            }
+            """;
+        String output = new JavacTask(TOOLBOX)
+                .sources(source)
+                .classpath(".")
+                .options("-encoding", "utf8", "--enable-preview", "-source", JAVA_VERSION)
+                .run()
+                .writeAll()
+                .getOutput(Task.OutputKind.DIRECT);
+
+        if (output.contains("compiler.err")) {
+            throw new RuntimeException("Error detected");
+        }
+    }
+
+    /*
+     * Test source for unsuccessful compile and specific error.
+     */
+    static void compFail(String code) {
+        String source = """
+            import java.lang.*;
+            import java.util.*;
+            import static java.lang.StringTemplate.RAW;
+            public class TEST {
+                public static void main(String... arg) {
+            """ +
+            code.indent(8) +
+            """
+                }
+            }
+            """;
+        String errors = new JavacTask(TOOLBOX)
+                .sources(source)
+                .classpath(".")
+                .options("-XDrawDiagnostics", "-encoding", "utf8", "--enable-preview", "-source", JAVA_VERSION)
+                .run(Task.Expect.FAIL)
+                .writeAll()
+                .getOutput(Task.OutputKind.DIRECT);
+
+        if (!errors.contains("compiler.err")) {
+            throw new RuntimeException("No error detected");
+        }
+    }
+}

test/langtools/tools/javac/template/TreeScannerTest.java

@@ -0,0 +1,107 @@
+/*
+ * Copyright (c) 2023, Oracle and/or its affiliates. All rights reserved.
+ * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
+ *
+ * This code is free software; you can redistribute it and/or modify it
+ * under the terms of the GNU General Public License version 2 only, as
+ * published by the Free Software Foundation.
+ *
+ * This code is distributed in the hope that it will be useful, but WITHOUT
+ * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
+ * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
+ * version 2 for more details (a copy is included in the LICENSE file that
+ * accompanied this code).
+ *
+ * You should have received a copy of the GNU General Public License version
+ * 2 along with this work; if not, write to the Free Software Foundation,
+ * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
+ *
+ * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
+ * or visit www.oracle.com if you need additional information or have any
+ * questions.
+ */
+
+/*
+ * @test
+ * @summary Verify proper behavior of TreeScanner w.r.t. templated Strings
+ * @modules jdk.compiler
+ */
+
+import java.io.*;
+import java.util.*;
+import javax.tools.*;
+import com.sun.source.tree.*;
+import com.sun.source.util.*;
+import java.net.URI;
+import java.net.URISyntaxException;
+
+public class TreeScannerTest {
+    private static final String JAVA_VERSION = System.getProperty("java.specification.version");
+
+    public static void main(String... args) throws Exception {
+        JavaCompiler compiler = ToolProvider.getSystemJavaCompiler();
+        String code = """
+                      public class Test {
+                          private void test(int a) {
+                              String s1 = TEST."p\\{a}s";
+                              String s2 = "p\\{a}s";
+                          }
+                      }
+                      """;
+        JavacTask task = (JavacTask) compiler.getTask(null, null, null,
+            List.of("--enable-preview", "-source", JAVA_VERSION), null, List.of(new TestJFO(code)));
+        StringBuilder output = new StringBuilder();
+        TreeScanner<Void,Void> checker = new TreeScanner<Void, Void>() {
+            private boolean log;
+
+            @Override
+            public Void visitStringTemplate(StringTemplateTree node, Void p) {
+                boolean prevLog = log;
+                try {
+                    log = true;
+                    return super.visitStringTemplate(node, p);
+                } finally {
+                    log = prevLog;
+                }
+            }
+
+            @Override
+            public Void scan(Tree tree, Void p) {
+                if (log) {
+                    output.append("(");
+                    output.append(tree != null ? tree.getKind() : "null");
+                    try {
+                        return super.scan(tree, p);
+                    } finally {
+                        output.append(")");
+                    }
+                } else {
+                    return super.scan(tree, p);
+                }
+            }
+
+        };
+
+        checker.scan(task.parse(), null);
+
+        String expected = "(IDENTIFIER)(IDENTIFIER)(null)(IDENTIFIER)";
+        if (!expected.equals(output.toString())) {
+            throw new AssertionError("expected output not found, found: " + output);
+        }
+    }
+
+    private static final class TestJFO extends SimpleJavaFileObject {
+        private final String code;
+
+        public TestJFO(String code) throws URISyntaxException, IOException {
+            super(new URI("mem://Test.java"), Kind.SOURCE);
+            this.code = code;
+        }
+
+        @Override
+        public CharSequence getCharContent(boolean ignoreEncodingErrors) throws IOException {
+            return code;
+        }
+
+    }
+}

test/langtools/tools/javac/tree/TreeKindTest.java

@@ -123,6 +123,10 @@ public class TreeKindTest {
                 ok = ok & verify(k, i, i == OpensTree.class);
                 break;
 
+            case TEMPLATE:
+                ok = ok & verify(k, i, i == StringTemplateTree.class);
+                break;
+
             case OTHER:
                 ok = ok & verify(k, i, i == null);
                 break;

test/micro/org/openjdk/bench/java/lang/StringTemplateFMT.java

@@ -0,0 +1,78 @@
+/*
+ * Copyright (c) 2023, Oracle and/or its affiliates. All rights reserved.
+ * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
+ *
+ * This code is free software; you can redistribute it and/or modify it
+ * under the terms of the GNU General Public License version 2 only, as
+ * published by the Free Software Foundation.
+ *
+ * This code is distributed in the hope that it will be useful, but WITHOUT
+ * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
+ * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
+ * version 2 for more details (a copy is included in the LICENSE file that
+ * accompanied this code).
+ *
+ * You should have received a copy of the GNU General Public License version
+ * 2 along with this work; if not, write to the Free Software Foundation,
+ * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
+ *
+ * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
+ * or visit www.oracle.com if you need additional information or have any
+ * questions.
+ */
+package org.openjdk.bench.java.lang;
+
+import org.openjdk.jmh.annotations.Benchmark;
+import org.openjdk.jmh.annotations.BenchmarkMode;
+import org.openjdk.jmh.annotations.Fork;
+import org.openjdk.jmh.annotations.Measurement;
+import org.openjdk.jmh.annotations.Mode;
+import org.openjdk.jmh.annotations.OutputTimeUnit;
+import org.openjdk.jmh.annotations.Scope;
+import org.openjdk.jmh.annotations.State;
+import org.openjdk.jmh.annotations.Warmup;
+
+import java.util.concurrent.TimeUnit;
+
+import static java.util.FormatProcessor.FMT;
+
+/*
+ * This benchmark measures StringTemplate.FMT FormatProcessor performance;
+ * exactly mirroring {@link org.openjdk.bench.java.lang.StringFormat} benchmark
+ */
+@BenchmarkMode(Mode.AverageTime)
+@OutputTimeUnit(TimeUnit.NANOSECONDS)
+@State(Scope.Benchmark)
+@Warmup(iterations = 5, time = 1)
+@Measurement(iterations = 5, time = 1)
+@Fork(value = 3, jvmArgsAppend = "--enable-preview")
+public class StringTemplateFMT {
+
+    public String s = "str";
+    public int i = 17;
+
+    @Benchmark
+    public String stringFormat() {
+        return FMT."%s\{s}";
+    }
+
+    @Benchmark
+    public String stringIntFormat() {
+        return FMT."%s\{s} %d\{i}";
+    }
+
+    @Benchmark
+    public String widthStringFormat() {
+        return FMT."%3s\{s}";
+    }
+
+    @Benchmark
+    public String widthStringIntFormat() {
+        return FMT."%3s\{s} %d\{i}";
+    }
+
+    @Benchmark
+    public String complexFormat() {
+        return FMT."%3s\{s} %10d\{i} %4S\{s} %04X\{i} %4S\{s} %04X\{i} %4S\{s} %04X\{i}";
+    }
+}