jdk/test/java/util/Random/DistinctSeeds.java

/*
 * 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).
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 * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
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/*
 * This file is available under and governed by the GNU General Public
 * License version 2 only, as published by the Free Software Foundation.
 * However, the following notice accompanied the original version of this
 * file:
 *
 * Written by Doug Lea with assistance from members of JCP JSR-166
 * Expert Group and released to the public domain, as explained at
 * http://creativecommons.org/licenses/publicdomain
 */

/*
 * @test
 * @bug 4949279
 * @summary Independent instantiations of Random() have distinct seeds.
 */

import java.util.Random;

public class DistinctSeeds {
    public static void main(String[] args) throws Exception {
        // Strictly speaking, it is possible for these to randomly fail,
        // but the probability should be *extremely* small (< 2**-63).
        if (new Random().nextLong() == new Random().nextLong() ||
            new Random().nextLong() == new Random().nextLong())
            throw new RuntimeException("Random() seeds not unique.");
    }
}