8200436: String::isBlank

Reviewed-by: sundar

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

@@ -2728,6 +2728,31 @@ public final class String
         return ret == null ? this : ret;
     }
 
+    /**
+     * Returns {@code true} if the string is empty or contains only
+     * {@link Character#isWhitespace(int) white space} codepoints,
+     * otherwise {@code false}.
+     *
+     * @return {@code true} if the string is empty or contains only
+     *         {@link Character#isWhitespace(int) white space} codepoints,
+     *         otherwise {@code false}
+     *
+     * @see Character#isWhitespace(int)
+     *
+     * @since 11
+     */
+    public boolean isBlank() {
+        return indexOfNonWhitespace() == length();
+    }
+
+    private int indexOfNonWhitespace() {
+        if (isLatin1()) {
+            return StringLatin1.indexOfNonWhitespace(value);
+        } else {
+            return StringUTF16.indexOfNonWhitespace(value);
+        }
+    }
+
     /**
      * This object (which is already a string!) is itself returned.
      *

test/jdk/java/lang/String/IsBlank.java

@@ -0,0 +1,74 @@
+/*
+ * Copyright (c) 2018, 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.util.stream.Collectors;
+import java.util.stream.IntStream;
+
+/**
+ * @test
+ * @summary Basic isBlank functionality
+ * @bug 8200436
+ * @run main/othervm IsBlank
+ */
+
+public class IsBlank {
+   public static void main(String... arg) {
+        testIsBlank();
+        testWhitespace();
+    }
+
+    /*
+     * Test with strings
+     */
+    static void testIsBlank() {
+        test("", true);
+        test(" ", true);
+        test(" \t", true);
+        test("  \u1680", true);
+        test("   abc   ", false);
+        test("   abc\u2022", false);
+    }
+
+    /*
+     * Test full whitespace range
+     */
+    static void testWhitespace() {
+        StringBuilder sb = new StringBuilder(64);
+        IntStream.range(1, 0xFFFF).filter(c -> Character.isWhitespace(c))
+                .forEach(c -> sb.append((char)c));
+        String whiteSpace = sb.toString();
+
+        test(whiteSpace, true);
+        test(whiteSpace + "abc" + whiteSpace, false);
+    }
+
+    /*
+     * Raise an exception if the two inputs are not equivalent.
+     */
+    static void test(String input, boolean expected) {
+        if (input.isBlank() != expected) {
+            System.err.format("Failed test, Input: %s, Expected: %b%n", input, expected);
+            throw new RuntimeException();
+        }
+    }
+}