8072727: add variation of Stream.iterate() that's finite

Reviewed-by: psandoz, briangoetz

jdk/src/java.base/share/classes/java/util/stream/DoubleStream.java

@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 2012, 2015, Oracle and/or its affiliates. All rights reserved.
+ * Copyright (c) 2012, 2016, 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
@@ -949,24 +949,100 @@ public interface DoubleStream extends BaseStream<Double, DoubleStream> {
      */
     public static DoubleStream iterate(final double seed, final DoubleUnaryOperator f) {
         Objects.requireNonNull(f);
-        final PrimitiveIterator.OfDouble iterator = new PrimitiveIterator.OfDouble() {
+        Spliterator.OfDouble spliterator = new Spliterators.AbstractDoubleSpliterator(Long.MAX_VALUE,
-            double t = seed;
+               Spliterator.ORDERED | Spliterator.IMMUTABLE | Spliterator.NONNULL) {
+            double prev;
+            boolean started;
 
             @Override
-            public boolean hasNext() {
+            public boolean tryAdvance(DoubleConsumer action) {
+                Objects.requireNonNull(action);
+                double t;
+                if (started)
+                    t = f.applyAsDouble(prev);
+                else {
+                    t = seed;
+                    started = true;
+                }
+                action.accept(prev = t);
+                return true;
+            }
+        };
+        return StreamSupport.doubleStream(spliterator, false);
+    }
+
+    /**
+     * Returns a sequential ordered {@code DoubleStream} produced by iterative
+     * application of a function to an initial element, conditioned on
+     * satisfying the supplied predicate.  The stream terminates as soon as
+     * the predicate returns false.
+     *
+     * <p>
+     * {@code DoubleStream.iterate} should produce the same sequence of
+     * elements as produced by the corresponding for-loop:
+     * <pre>{@code
+     *     for (double index=seed; predicate.test(index); index = f.apply(index)) {
+     *         ...
+     *     }
+     * }</pre>
+     *
+     * <p>
+     * The resulting sequence may be empty if the predicate does not hold on
+     * the seed value.  Otherwise the first element will be the supplied seed
+     * value, the next element (if present) will be the result of applying the
+     * function f to the seed value, and so on iteratively until the predicate
+     * indicates that the stream should terminate.
+     *
+     * @param seed the initial element
+     * @param predicate a predicate to apply to elements to determine when the
+     *          stream must terminate.
+     * @param f a function to be applied to the previous element to produce
+     *          a new element
+     * @return a new sequential {@code DoubleStream}
+     * @since 9
+     */
+    public static DoubleStream iterate(double seed, DoublePredicate predicate, DoubleUnaryOperator f) {
+        Objects.requireNonNull(f);
+        Objects.requireNonNull(predicate);
+        Spliterator.OfDouble spliterator = new Spliterators.AbstractDoubleSpliterator(Long.MAX_VALUE,
+               Spliterator.ORDERED | Spliterator.IMMUTABLE | Spliterator.NONNULL) {
+            double prev;
+            boolean started, finished;
+
+            @Override
+            public boolean tryAdvance(DoubleConsumer action) {
+                Objects.requireNonNull(action);
+                if (finished)
+                    return false;
+                double t;
+                if (started)
+                    t = f.applyAsDouble(prev);
+                else {
+                    t = seed;
+                    started = true;
+                }
+                if (!predicate.test(t)) {
+                    finished = true;
+                    return false;
+                }
+                action.accept(prev = t);
                 return true;
             }
 
             @Override
-            public double nextDouble() {
+            public void forEachRemaining(DoubleConsumer action) {
-                double v = t;
+                Objects.requireNonNull(action);
-                t = f.applyAsDouble(t);
+                if (finished)
-                return v;
+                    return;
+                finished = true;
+                double t = started ? f.applyAsDouble(prev) : seed;
+                while (predicate.test(t)) {
+                    action.accept(t);
+                    t = f.applyAsDouble(t);
+                }
             }
         };
-        return StreamSupport.doubleStream(Spliterators.spliteratorUnknownSize(
+        return StreamSupport.doubleStream(spliterator, false);
-                iterator,
-                Spliterator.ORDERED | Spliterator.IMMUTABLE | Spliterator.NONNULL), false);
     }
 
     /**

jdk/src/java.base/share/classes/java/util/stream/IntStream.java

@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 2012, 2015, Oracle and/or its affiliates. All rights reserved.
+ * Copyright (c) 2012, 2016, 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
@@ -885,28 +885,104 @@ public interface IntStream extends BaseStream<Integer, IntStream> {
      * @param seed the initial element
      * @param f a function to be applied to the previous element to produce
      *          a new element
-     * @return A new sequential {@code IntStream}
+     * @return a new sequential {@code IntStream}
      */
     public static IntStream iterate(final int seed, final IntUnaryOperator f) {
         Objects.requireNonNull(f);
-        final PrimitiveIterator.OfInt iterator = new PrimitiveIterator.OfInt() {
+        Spliterator.OfInt spliterator = new Spliterators.AbstractIntSpliterator(Long.MAX_VALUE,
-            int t = seed;
+               Spliterator.ORDERED | Spliterator.IMMUTABLE | Spliterator.NONNULL) {
+            int prev;
+            boolean started;
 
             @Override
-            public boolean hasNext() {
+            public boolean tryAdvance(IntConsumer action) {
+                Objects.requireNonNull(action);
+                int t;
+                if (started)
+                    t = f.applyAsInt(prev);
+                else {
+                    t = seed;
+                    started = true;
+                }
+                action.accept(prev = t);
+                return true;
+            }
+        };
+        return StreamSupport.intStream(spliterator, false);
+    }
+
+    /**
+     * Returns a sequential ordered {@code IntStream} produced by iterative
+     * application of a function to an initial element, conditioned on
+     * satisfying the supplied predicate.  The stream terminates as soon as
+     * the predicate returns false.
+     *
+     * <p>
+     * {@code IntStream.iterate} should produce the same sequence of elements
+     * as produced by the corresponding for-loop:
+     * <pre>{@code
+     *     for (int index=seed; predicate.test(index); index = f.apply(index)) {
+     *         ...
+     *     }
+     * }</pre>
+     *
+     * <p>
+     * The resulting sequence may be empty if the predicate does not hold on
+     * the seed value.  Otherwise the first element will be the supplied seed
+     * value, the next element (if present) will be the result of applying the
+     * function f to the seed value, and so on iteratively until the predicate
+     * indicates that the stream should terminate.
+     *
+     * @param seed the initial element
+     * @param predicate a predicate to apply to elements to determine when the
+     *          stream must terminate.
+     * @param f a function to be applied to the previous element to produce
+     *          a new element
+     * @return a new sequential {@code IntStream}
+     * @since 9
+     */
+    public static IntStream iterate(int seed, IntPredicate predicate, IntUnaryOperator f) {
+        Objects.requireNonNull(f);
+        Objects.requireNonNull(predicate);
+        Spliterator.OfInt spliterator = new Spliterators.AbstractIntSpliterator(Long.MAX_VALUE,
+               Spliterator.ORDERED | Spliterator.IMMUTABLE | Spliterator.NONNULL) {
+            int prev;
+            boolean started, finished;
+
+            @Override
+            public boolean tryAdvance(IntConsumer action) {
+                Objects.requireNonNull(action);
+                if (finished)
+                    return false;
+                int t;
+                if (started)
+                    t = f.applyAsInt(prev);
+                else {
+                    t = seed;
+                    started = true;
+                }
+                if (!predicate.test(t)) {
+                    finished = true;
+                    return false;
+                }
+                action.accept(prev = t);
                 return true;
             }
 
             @Override
-            public int nextInt() {
+            public void forEachRemaining(IntConsumer action) {
-                int v = t;
+                Objects.requireNonNull(action);
-                t = f.applyAsInt(t);
+                if (finished)
-                return v;
+                    return;
+                finished = true;
+                int t = started ? f.applyAsInt(prev) : seed;
+                while (predicate.test(t)) {
+                    action.accept(t);
+                    t = f.applyAsInt(t);
+                }
             }
         };
-        return StreamSupport.intStream(Spliterators.spliteratorUnknownSize(
+        return StreamSupport.intStream(spliterator, false);
-                iterator,
-                Spliterator.ORDERED | Spliterator.IMMUTABLE | Spliterator.NONNULL), false);
     }
 
     /**

jdk/src/java.base/share/classes/java/util/stream/LongStream.java

@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 2013, 2015, Oracle and/or its affiliates. All rights reserved.
+ * Copyright (c) 2013, 2016, 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
@@ -879,24 +879,100 @@ public interface LongStream extends BaseStream<Long, LongStream> {
      */
     public static LongStream iterate(final long seed, final LongUnaryOperator f) {
         Objects.requireNonNull(f);
-        final PrimitiveIterator.OfLong iterator = new PrimitiveIterator.OfLong() {
+        Spliterator.OfLong spliterator = new Spliterators.AbstractLongSpliterator(Long.MAX_VALUE,
-            long t = seed;
+               Spliterator.ORDERED | Spliterator.IMMUTABLE | Spliterator.NONNULL) {
+            long prev;
+            boolean started;
 
             @Override
-            public boolean hasNext() {
+            public boolean tryAdvance(LongConsumer action) {
+                Objects.requireNonNull(action);
+                long t;
+                if (started)
+                    t = f.applyAsLong(prev);
+                else {
+                    t = seed;
+                    started = true;
+                }
+                action.accept(prev = t);
+                return true;
+            }
+        };
+        return StreamSupport.longStream(spliterator, false);
+    }
+
+    /**
+     * Returns a sequential ordered {@code LongStream} produced by iterative
+     * application of a function to an initial element, conditioned on
+     * satisfying the supplied predicate.  The stream terminates as soon as
+     * the predicate returns false.
+     *
+     * <p>
+     * {@code LongStream.iterate} should produce the same sequence of elements
+     * as produced by the corresponding for-loop:
+     * <pre>{@code
+     *     for (long index=seed; predicate.test(index); index = f.apply(index)) {
+     *         ...
+     *     }
+     * }</pre>
+     *
+     * <p>
+     * The resulting sequence may be empty if the predicate does not hold on
+     * the seed value.  Otherwise the first element will be the supplied seed
+     * value, the next element (if present) will be the result of applying the
+     * function f to the seed value, and so on iteratively until the predicate
+     * indicates that the stream should terminate.
+     *
+     * @param seed the initial element
+     * @param predicate a predicate to apply to elements to determine when the
+     *          stream must terminate.
+     * @param f a function to be applied to the previous element to produce
+     *          a new element
+     * @return a new sequential {@code LongStream}
+     * @since 9
+     */
+    public static LongStream iterate(long seed, LongPredicate predicate, LongUnaryOperator f) {
+        Objects.requireNonNull(f);
+        Objects.requireNonNull(predicate);
+        Spliterator.OfLong spliterator = new Spliterators.AbstractLongSpliterator(Long.MAX_VALUE,
+               Spliterator.ORDERED | Spliterator.IMMUTABLE | Spliterator.NONNULL) {
+            long prev;
+            boolean started, finished;
+
+            @Override
+            public boolean tryAdvance(LongConsumer action) {
+                Objects.requireNonNull(action);
+                if (finished)
+                    return false;
+                long t;
+                if (started)
+                    t = f.applyAsLong(prev);
+                else {
+                    t = seed;
+                    started = true;
+                }
+                if (!predicate.test(t)) {
+                    finished = true;
+                    return false;
+                }
+                action.accept(prev = t);
                 return true;
             }
 
             @Override
-            public long nextLong() {
+            public void forEachRemaining(LongConsumer action) {
-                long v = t;
+                Objects.requireNonNull(action);
-                t = f.applyAsLong(t);
+                if (finished)
-                return v;
+                    return;
+                finished = true;
+                long t = started ? f.applyAsLong(prev) : seed;
+                while (predicate.test(t)) {
+                    action.accept(t);
+                    t = f.applyAsLong(t);
+                }
             }
         };
-        return StreamSupport.longStream(Spliterators.spliteratorUnknownSize(
+        return StreamSupport.longStream(spliterator, false);
-                iterator,
-                Spliterator.ORDERED | Spliterator.IMMUTABLE | Spliterator.NONNULL), false);
     }
 
     /**

jdk/src/java.base/share/classes/java/util/stream/Stream.java

@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 2012, 2015, Oracle and/or its affiliates. All rights reserved.
+ * Copyright (c) 2012, 2016, 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
@@ -29,7 +29,6 @@ import java.nio.file.Path;
 import java.util.Arrays;
 import java.util.Collection;
 import java.util.Comparator;
-import java.util.Iterator;
 import java.util.Objects;
 import java.util.Optional;
 import java.util.Spliterator;
@@ -1185,23 +1184,103 @@ public interface Stream<T> extends BaseStream<T, Stream<T>> {
      */
     public static<T> Stream<T> iterate(final T seed, final UnaryOperator<T> f) {
         Objects.requireNonNull(f);
-        final Iterator<T> iterator = new Iterator<T>() {
+        Spliterator<T> spliterator = new Spliterators.AbstractSpliterator<>(Long.MAX_VALUE,
-            @SuppressWarnings("unchecked")
+               Spliterator.ORDERED | Spliterator.IMMUTABLE) {
-            T t = (T) Streams.NONE;
+            T prev;
+            boolean started;
 
             @Override
-            public boolean hasNext() {
+            public boolean tryAdvance(Consumer<? super T> action) {
+                Objects.requireNonNull(action);
+                T t;
+                if (started)
+                    t = f.apply(prev);
+                else {
+                    t = seed;
+                    started = true;
+                }
+                action.accept(prev = t);
+                return true;
+            }
+        };
+        return StreamSupport.stream(spliterator, false);
+    }
+
+    /**
+     * Returns a sequential ordered {@code Stream} produced by iterative
+     * application of a function to an initial element, conditioned on
+     * satisfying the supplied predicate.  The stream terminates as soon as
+     * the predicate returns false.
+     *
+     * <p>
+     * {@code Stream.iterate} should produce the same sequence of elements as
+     * produced by the corresponding for-loop:
+     * <pre>{@code
+     *     for (T index=seed; predicate.test(index); index = f.apply(index)) {
+     *         ...
+     *     }
+     * }</pre>
+     *
+     * <p>
+     * The resulting sequence may be empty if the predicate does not hold on
+     * the seed value.  Otherwise the first element will be the supplied seed
+     * value, the next element (if present) will be the result of applying the
+     * function f to the seed value, and so on iteratively until the predicate
+     * indicates that the stream should terminate.
+     *
+     * @param <T> the type of stream elements
+     * @param seed the initial element
+     * @param predicate a predicate to apply to elements to determine when the
+     *          stream must terminate.
+     * @param f a function to be applied to the previous element to produce
+     *          a new element
+     * @return a new sequential {@code Stream}
+     * @since 9
+     */
+    public static<T> Stream<T> iterate(T seed, Predicate<? super T> predicate, UnaryOperator<T> f) {
+        Objects.requireNonNull(f);
+        Objects.requireNonNull(predicate);
+        Spliterator<T> spliterator = new Spliterators.AbstractSpliterator<>(Long.MAX_VALUE,
+               Spliterator.ORDERED | Spliterator.IMMUTABLE) {
+            T prev;
+            boolean started, finished;
+
+            @Override
+            public boolean tryAdvance(Consumer<? super T> action) {
+                Objects.requireNonNull(action);
+                if (finished)
+                    return false;
+                T t;
+                if (started)
+                    t = f.apply(prev);
+                else {
+                    t = seed;
+                    started = true;
+                }
+                if (!predicate.test(t)) {
+                    prev = null;
+                    finished = true;
+                    return false;
+                }
+                action.accept(prev = t);
                 return true;
             }
 
             @Override
-            public T next() {
+            public void forEachRemaining(Consumer<? super T> action) {
-                return t = (t == Streams.NONE) ? seed : f.apply(t);
+                Objects.requireNonNull(action);
+                if (finished)
+                    return;
+                finished = true;
+                T t = started ? f.apply(prev) : seed;
+                prev = null;
+                while (predicate.test(t)) {
+                    action.accept(t);
+                    t = f.apply(t);
+                }
             }
         };
-        return StreamSupport.stream(Spliterators.spliteratorUnknownSize(
+        return StreamSupport.stream(spliterator, false);
-                iterator,
-                Spliterator.ORDERED | Spliterator.IMMUTABLE), false);
     }
 
     /**

jdk/src/java.base/share/classes/java/util/stream/Streams.java

@@ -48,14 +48,6 @@ final class Streams {
         throw new Error("no instances");
     }
 
-    /**
-     * An object instance representing no value, that cannot be an actual
-     * data element of a stream.  Used when processing streams that can contain
-     * {@code null} elements to distinguish between a {@code null} value and no
-     * value.
-     */
-    static final Object NONE = new Object();
-
     /**
      * An {@code int} range spliterator.
      */

jdk/test/java/util/stream/bootlib/java.base/java/util/stream/DoubleStreamTestDataProvider.java

@@ -126,6 +126,9 @@ public class DoubleStreamTestDataProvider {
                                             () -> Spliterators.spliterator(isl.iterator(), doubles.length, 0)));
                 spliterators.add(splitDescr("Primitives.s(SpinedBuffer.iterator()):" + name,
                                             () -> Spliterators.spliteratorUnknownSize(isl.iterator(), 0)));
+                spliterators.add(splitDescr("DoubleStream.iterate(0,x->x<l;x->x+1):" + name,
+                                            () -> DoubleStream.iterate(0.0, x -> x < doubles.length, x -> x + 1.0)
+                                                              .spliterator()));
                 // Need more!
             }
             spliteratorTestData = spliterators.toArray(new Object[0][]);

jdk/test/java/util/stream/bootlib/java.base/java/util/stream/IntStreamTestDataProvider.java

@@ -136,6 +136,8 @@ public class IntStreamTestDataProvider {
                                             () -> IntStream.range(0, ints.length).spliterator()));
                 spliterators.add(splitDescr("IntStream.intRangeClosed(0,l):" + name,
                                             () -> IntStream.rangeClosed(0, ints.length).spliterator()));
+                spliterators.add(splitDescr("IntStream.iterate(0,x->x<l,x->x+1): " + name,
+                                            () -> IntStream.iterate(0, x -> x < ints.length, x -> x + 1).spliterator()));
                 // Need more!
             }
             spliteratorTestData = spliterators.toArray(new Object[0][]);

jdk/test/java/util/stream/bootlib/java.base/java/util/stream/LongStreamTestDataProvider.java

@@ -136,6 +136,9 @@ public class LongStreamTestDataProvider {
                                             () -> LongStream.range(0, longs.length).spliterator()));
                 spliterators.add(splitDescr("LongStream.longRangeClosed(0,l):" + name,
                                             () -> LongStream.rangeClosed(0, longs.length).spliterator()));
+                spliterators.add(splitDescr("LongStream.iterate(0,x->x<l;x->x+1):" + name,
+                                            () -> LongStream.iterate(0L, x -> x < longs.length, x -> x + 1L)
+                                                            .spliterator()));
                 // Need more!
             }
             spliteratorTestData = spliterators.toArray(new Object[0][]);

jdk/test/java/util/stream/bootlib/java.base/java/util/stream/StreamTestDataProvider.java

@@ -171,6 +171,8 @@ public class StreamTestDataProvider {
                                             () -> Spliterators.spliterator(Arrays.asList(ints).iterator(), ints.length, 0)));
                 spliterators.add(splitDescr("Iterators.s(Arrays.s(array).iterator()):" + name,
                                             () -> Spliterators.spliteratorUnknownSize(Arrays.asList(ints).iterator(), 0)));
+                spliterators.add(splitDescr("Stream.iterate(0,x->x<l,x->x+1): " + name,
+                                            () -> Stream.iterate(0, x -> x < ints.length, x -> x + 1).spliterator()));
                 // @@@ Add map and collection spliterators when spliterator() is exposed on Collection or Iterable
             }
             spliteratorTestData = spliterators.toArray(new Object[0][]);

jdk/test/java/util/stream/test/org/openjdk/tests/java/util/stream/IterateTest.java

@@ -0,0 +1,100 @@
+/*
+ * Copyright (c) 2016, 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 8072727
+ */
+
+package org.openjdk.tests.java.util.stream;
+
+import java.util.List;
+import java.util.Objects;
+import java.util.stream.DoubleStream;
+import java.util.stream.IntStream;
+import java.util.stream.LongStream;
+import java.util.stream.OpTestCase;
+import java.util.stream.Stream;
+import java.util.stream.TestData;
+import java.util.stream.TestData.Factory;
+
+import static java.util.stream.ThowableHelper.checkNPE;
+
+import org.testng.annotations.DataProvider;
+import org.testng.annotations.Test;
+
+@Test
+public class IterateTest extends OpTestCase {
+
+    @DataProvider(name = "IterateStreamsData")
+    public static Object[][] makeIterateStreamsTestData() {
+        Object[][] data = {
+            {List.of(),
+                Factory.ofSupplier("ref.empty", () -> Stream.iterate(1, x -> x < 0, x -> x * 2))},
+            {List.of(1),
+                Factory.ofSupplier("ref.one", () -> Stream.iterate(1, x -> x < 2, x -> x * 2))},
+            {List.of(1, 2, 4, 8, 16, 32, 64, 128, 256, 512),
+                Factory.ofSupplier("ref.ten", () -> Stream.iterate(1, x -> x < 1000, x -> x * 2))},
+            {List.of(10, 9, 8, 7, 6, 5, 4, 3, 2, 1, 0),
+                Factory.ofSupplier("ref.nullCheck", () -> Stream.iterate(10, Objects::nonNull, x -> x > 0 ? x - 1 : null))},
+            {List.of(),
+                Factory.ofIntSupplier("int.empty", () -> IntStream.iterate(1, x -> x < 0, x -> x + 1))},
+            {List.of(1),
+                Factory.ofIntSupplier("int.one", () -> IntStream.iterate(1, x -> x < 2, x -> x + 1))},
+            {List.of(1, 2, 3, 4, 5, 6, 7, 8, 9, 10),
+                Factory.ofIntSupplier("int.ten", () -> IntStream.iterate(1, x -> x <= 10, x -> x + 1))},
+            {List.of(5, 4, 3, 2, 1),
+                Factory.ofIntSupplier("int.divZero", () -> IntStream.iterate(5, x -> x != 0, x -> x - 1/x/2 - 1))},
+            {List.of(),
+                Factory.ofLongSupplier("long.empty", () -> LongStream.iterate(1L, x -> x < 0, x -> x + 1))},
+            {List.of(1L),
+                Factory.ofLongSupplier("long.one", () -> LongStream.iterate(1L, x -> x < 2, x -> x + 1))},
+            {List.of(1L, 2L, 3L, 4L, 5L, 6L, 7L, 8L, 9L, 10L),
+                Factory.ofLongSupplier("long.ten", () -> LongStream.iterate(1L, x -> x <= 10, x -> x + 1))},
+            {List.of(),
+                Factory.ofDoubleSupplier("double.empty", () -> DoubleStream.iterate(1.0, x -> x < 0, x -> x + 1))},
+            {List.of(1.0),
+                Factory.ofDoubleSupplier("double.one", () -> DoubleStream.iterate(1.0, x -> x < 2, x -> x + 1))},
+            {List.of(1.0, 2.0, 3.0, 4.0, 5.0, 6.0, 7.0, 8.0, 9.0, 10.0),
+                Factory.ofDoubleSupplier("double.ten", () -> DoubleStream.iterate(1.0, x -> x <= 10, x -> x + 1))}
+        };
+        return data;
+    }
+
+    @Test(dataProvider = "IterateStreamsData")
+    public <T> void testIterate(List<T> expected, TestData<T, ?> data) {
+        withData(data).stream(s -> s).expectedResult(expected).exercise();
+    }
+
+    @Test
+    public void testNPE() {
+        checkNPE(() -> Stream.iterate("", null, x -> x + "a"));
+        checkNPE(() -> Stream.iterate("", String::isEmpty, null));
+        checkNPE(() -> IntStream.iterate(0, null, x -> x + 1));
+        checkNPE(() -> IntStream.iterate(0, x -> x < 10, null));
+        checkNPE(() -> LongStream.iterate(0, null, x -> x + 1));
+        checkNPE(() -> LongStream.iterate(0, x -> x < 10, null));
+        checkNPE(() -> DoubleStream.iterate(0, null, x -> x + 1));
+        checkNPE(() -> DoubleStream.iterate(0, x -> x < 10, null));
+    }
+}