8294693: Add Collections.shuffle overload that accepts RandomGenerator interface
Reviewed-by: smarks, darcy
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@ -1,5 +1,5 @@
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/*
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* Copyright (c) 1997, 2022, Oracle and/or its affiliates. All rights reserved.
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* Copyright (c) 1997, 2023, Oracle and/or its affiliates. All rights reserved.
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* DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
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*
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* This code is free software; you can redistribute it and/or modify it
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@ -37,6 +37,7 @@ import java.util.function.Function;
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import java.util.function.IntFunction;
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import java.util.function.Predicate;
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import java.util.function.UnaryOperator;
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import java.util.random.RandomGenerator;
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import java.util.stream.IntStream;
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import java.util.stream.Stream;
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import java.util.stream.StreamSupport;
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@ -411,8 +412,8 @@ public class Collections {
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* portion of the list that runs from the first element to the current
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* position, inclusive.
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*
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* <p>This method runs in linear time. If the specified list does not
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* implement the {@link RandomAccess} interface and is large, this
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* @implSpec This method runs in linear time. If the specified list does
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* not implement the {@link RandomAccess} interface and is large, this
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* implementation dumps the specified list into an array before shuffling
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* it, and dumps the shuffled array back into the list. This avoids the
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* quadratic behavior that would result from shuffling a "sequential
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@ -431,6 +432,24 @@ public class Collections {
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private static Random r;
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/**
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* Randomly permute the specified list using the specified source of
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* randomness.<p>
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*
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* This method is equivalent to {@link #shuffle(List, RandomGenerator)}
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* and exists for backward compatibility. The {@link #shuffle(List, RandomGenerator)}
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* method is preferred, as it is not limited to random generators
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* that extend the {@link Random} class.
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*
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* @param list the list to be shuffled.
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* @param rnd the source of randomness to use to shuffle the list.
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* @throws UnsupportedOperationException if the specified list or its
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* list-iterator does not support the {@code set} operation.
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*/
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public static void shuffle(List<?> list, Random rnd) {
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shuffle(list, (RandomGenerator) rnd);
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}
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/**
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* Randomly permute the specified list using the specified source of
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* randomness. All permutations occur with equal likelihood
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@ -442,8 +461,8 @@ public class Collections {
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* portion of the list that runs from the first element to the current
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* position, inclusive.<p>
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*
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* This method runs in linear time. If the specified list does not
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* implement the {@link RandomAccess} interface and is large, this
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* @implSpec This method runs in linear time. If the specified list does
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* not implement the {@link RandomAccess} interface and is large, this
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* implementation dumps the specified list into an array before shuffling
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* it, and dumps the shuffled array back into the list. This avoids the
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* quadratic behavior that would result from shuffling a "sequential
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@ -453,9 +472,10 @@ public class Collections {
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* @param rnd the source of randomness to use to shuffle the list.
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* @throws UnsupportedOperationException if the specified list or its
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* list-iterator does not support the {@code set} operation.
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* @since 21
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*/
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@SuppressWarnings({"rawtypes", "unchecked"})
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public static void shuffle(List<?> list, Random rnd) {
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public static void shuffle(List<?> list, RandomGenerator rnd) {
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int size = list.size();
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if (size < SHUFFLE_THRESHOLD || list instanceof RandomAccess) {
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for (int i=size; i>1; i--)
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79
test/jdk/java/util/Collections/Shuffle.java
Normal file
79
test/jdk/java/util/Collections/Shuffle.java
Normal file
@ -0,0 +1,79 @@
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/*
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* Copyright (c) 2023, Oracle and/or its affiliates. All rights reserved.
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* DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
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*
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* This code is free software; you can redistribute it and/or modify it
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* under the terms of the GNU General Public License version 2 only, as
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* published by the Free Software Foundation.
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*
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* This code is distributed in the hope that it will be useful, but WITHOUT
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* ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
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* FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
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* version 2 for more details (a copy is included in the LICENSE file that
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* accompanied this code).
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*
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* You should have received a copy of the GNU General Public License version
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* 2 along with this work; if not, write to the Free Software Foundation,
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* Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
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*
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* Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
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* or visit www.oracle.com if you need additional information or have any
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* questions.
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*/
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/*
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* @test
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* @bug 8294693
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* @summary Basic test for Collections.shuffle
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* @key randomness
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*/
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import java.util.ArrayList;
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import java.util.Collections;
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import java.util.LinkedList;
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import java.util.List;
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import java.util.Random;
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import java.util.function.Consumer;
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import java.util.random.RandomGenerator;
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public class Shuffle {
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static final int N = 100;
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public static void main(String[] args) {
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test(new ArrayList<>());
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test(new LinkedList<>());
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}
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static void test(List<Integer> list) {
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for (int i = 0; i < N; i++) {
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list.add(i);
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}
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Collections.shuffle(list);
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if (list.size() != N) {
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throw new RuntimeException(list.getClass() + ": size " + list.size() + " != " + N);
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}
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for (int i = 0; i < N; i++) {
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if (!list.contains(i)) {
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throw new RuntimeException(list.getClass() + ": does not contain " + i);
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}
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}
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checkRandom(list, l -> Collections.shuffle(l, new Random(1)));
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RandomGenerator.JumpableGenerator generator = RandomGenerator.JumpableGenerator.of("Xoshiro256PlusPlus");
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checkRandom(list, l -> Collections.shuffle(l, generator.copy()));
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}
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private static void checkRandom(List<Integer> list, Consumer<List<?>> randomizer) {
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list.sort(null);
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randomizer.accept(list);
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ArrayList<Integer> copy = new ArrayList<>(list);
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list.sort(null);
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if (list.equals(copy)) {
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// Assume that at least one pair of elements must be reordered during shuffle
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throw new RuntimeException(list.getClass() + ": list is not shuffled");
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}
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randomizer.accept(list);
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if (!list.equals(copy)) {
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throw new RuntimeException(list.getClass() + ": " + list + " != " + copy);
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}
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}
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}
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