Java example source code file (HashMapCloneLeak.java)

This example Java source code file (HashMapCloneLeak.java) is included in the alvinalexander.com "Java Source Code Warehouse" project. The intent of this project is to help you "Learn Java by Example" ^TM.

Learn more about this Java project at its project page.

Java - Java tags/keywords

exception, hashmap, hashmapcloneleak, object, outofmemoryerror, util, weakreference

The HashMapCloneLeak.java Java example source code

/*
 * Copyright (c) 2013, 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 7042126
 * @summary Verify that we do not leak contents when we clone a HashMap
 * @author david.buck@oracle.com
 * @run main/othervm HashMapCloneLeak
 * @run main/othervm -XX:+AggressiveOpts HashMapCloneLeak
 */

import java.util.HashMap;
import java.lang.ref.WeakReference;

public class HashMapCloneLeak {

    static WeakReference<Object> wr = null;

    // helper method to keep testObject and map out of main method's scope
    private static HashMap<Integer, Object> makeMap() {
        HashMap<Integer, Object> map = new HashMap();
        Object testObject = new Object();
        wr = new WeakReference<Object>(testObject);
        map.put(42, testObject);
        return map;
    }

    public static void main(String[] args) throws Exception {
        HashMap<Integer, Object> hm = makeMap();
        hm = (HashMap<Integer, Object>)hm.clone();
        hm.clear();
        // There should no longer be a strong reference to testObject
        // the WeakReference should be nulled out by GC. If not,
        // we will hang here until timed out by the test harness.
        Object[] chain = null;
        while (wr.get() != null) {
            try {
                Object[] allocate = new Object[1000000];
                allocate[0] = chain;
                chain = allocate;
            } catch (OutOfMemoryError oome) {
                chain = null;
            }
            System.gc();
            Thread.sleep(100);
        }
    }

}