1 /*
 2  * Copyright (c) 2023, 2026, Oracle and/or its affiliates. All rights reserved.
 3  * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
 4  *
 5  * This code is free software; you can redistribute it and/or modify it
 6  * under the terms of the GNU General Public License version 2 only, as
 7  * published by the Free Software Foundation.
 8  *
 9  * This code is distributed in the hope that it will be useful, but WITHOUT
10  * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
11  * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
12  * version 2 for more details (a copy is included in the LICENSE file that
13  * accompanied this code).
14  *
15  * You should have received a copy of the GNU General Public License version
16  * 2 along with this work; if not, write to the Free Software Foundation,
17  * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
18  *
19  * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
20  * or visit www.oracle.com if you need additional information or have any
21  * questions.
22  */
23 
24 /*
25  * @test
26  * @bug     8294693
27  * @summary Basic test for Collections.shuffle
28  * @key     randomness
29  * @library /test/lib
30  */
31 
32 import jdk.test.lib.valueclass.VClass;
33 import java.util.ArrayList;
34 import java.util.Collections;
35 import java.util.LinkedList;
36 import java.util.List;
37 import java.util.Random;
38 import java.util.function.Consumer;
39 import java.util.random.RandomGenerator;
40 
41 public class Shuffle {
42     static final int N = 100;
43 
44     public static void main(String[] args) {
45         test(new ArrayList<>());
46         test(new LinkedList<>());
47         testValue();
48     }
49 
50     static void test(List<Integer> list) {
51         for (int i = 0; i < N; i++) {
52             list.add(i);
53         }
54         Collections.shuffle(list);
55         if (list.size() != N) {
56             throw new RuntimeException(list.getClass() + ": size " + list.size() + " != " + N);
57         }
58         for (int i = 0; i < N; i++) {
59             if (!list.contains(i)) {
60                 throw new RuntimeException(list.getClass() + ": does not contain " + i);
61             }
62         }
63         checkRandom(list, l -> Collections.shuffle(l, new Random(1)));
64         RandomGenerator.JumpableGenerator generator = RandomGenerator.JumpableGenerator.of("Xoshiro256PlusPlus");
65         checkRandom(list, l -> Collections.shuffle(l, generator.copy()));
66     }
67 
68     static void testValue() {
69         List<VClass> values = new ArrayList<>();
70         for (int i = 0; i < N; i++) values.add(new VClass(i, new int[] { i }));
71         Collections.shuffle(values, new Random(1));
72         if (values.size() != N) throw new RuntimeException("value shuffle size");
73         for (int i = 0; i < N; i++)
74             if (Collections.frequency(values, new VClass(i, new int[] { i })) != 1)
75                 throw new RuntimeException("value shuffle lost " + i);
76     }
77 
78     private static void checkRandom(List<Integer> list, Consumer<List<?>> randomizer) {
79         list.sort(null);
80         randomizer.accept(list);
81         ArrayList<Integer> copy = new ArrayList<>(list);
82         list.sort(null);
83         if (list.equals(copy)) {
84             // Assume that at least one pair of elements must be reordered during shuffle
85             throw new RuntimeException(list.getClass() + ": list is not shuffled");
86         }
87         randomizer.accept(list);
88         if (!list.equals(copy)) {
89             throw new RuntimeException(list.getClass() + ": " + list + " != " + copy);
90         }
91     }
92 }
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