Java example source code file (ReplaceExisting.java)

This example Java source code file (ReplaceExisting.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

collected, corrupt, entries, error, hashmap, hashset, illegalargumentexception, integer, iterator, replaceexisting, runtimeexception, util

The ReplaceExisting.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 8025173
 * @summary Verify that replacing the value for an existing key does not
 * corrupt active iterators, in particular due to a resize() occurring and
 * not updating modCount.
 * @run main ReplaceExisting
 */

import java.util.ConcurrentModificationException;
import java.util.HashMap;
import java.util.HashSet;
import java.util.Iterator;

public class ReplaceExisting {
    /* Number of entries required to trigger a resize for cap=16, load=0.75*/
    private static int ENTRIES = 13;

    public static void main(String[] args) {
        for (int i = 0; i <= ENTRIES; i++) {
            HashMap<Integer,Integer> hm = prepHashMap();
            testItr(hm, i);
        }
    }

    /* Prepare a HashMap that will resize on next put() */
    private static HashMap<Integer,Integer> prepHashMap() {
        HashMap<Integer,Integer> hm = new HashMap<>(16, 0.75f);
        // Add items to one more than the resize threshold
        for (int i = 0; i < ENTRIES; i++) {
            hm.put(i*10, i*10);
        }
        return hm;
    }

    /* Iterate hm for elemBeforePut elements, then call put() to replace value
     * for existing key.  With bug 8025173, this will also cause a resize, but
     * not increase the modCount.
     * Finish the iteration to check for a corrupt iterator.
     */
    private static void testItr(HashMap<Integer,Integer> hm, int elemBeforePut) {
        if (elemBeforePut > hm.size()) {
            throw new IllegalArgumentException("Error in test: elemBeforePut must be <= HashMap size");
        }
        // Create a copy of the keys
        HashSet<Integer> keys = new HashSet<>(hm.size());
        keys.addAll(hm.keySet());

        HashSet<Integer> collected = new HashSet<>(hm.size());

        // Run itr for elemBeforePut items, collecting returned elems
        Iterator<Integer> itr = hm.keySet().iterator();
        for (int i = 0; i < elemBeforePut; i++) {
            Integer retVal = itr.next();
            if (!collected.add(retVal)) {
                throw new RuntimeException("Corrupt iterator: key " + retVal + " already encountered");
            }
        }

        // Do put() to replace entry (and resize table when bug present)
        if (null == hm.put(0, 100)) {
            throw new RuntimeException("Error in test: expected key 0 to be in the HashMap");
        }

        // Finish itr + collecting returned elems
        while(itr.hasNext()) {
            Integer retVal = itr.next();
            if (!collected.add(retVal)) {
                throw new RuntimeException("Corrupt iterator: key " + retVal + " already encountered");
            }
        }

        // Compare returned elems to original copy of keys
        if (!keys.equals(collected)) {
            throw new RuntimeException("Collected keys do not match original set of keys");
        }
    }
}