Commons Collections example source code file (TestReferenceMap.java)

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

Java - Commons Collections tags/keywords

in, map, map, nullpointerexception, nullpointerexception, object, object, outofmemoryerror, ram, string, testreferencemap, util, weak, weakreference, weakreference

The Commons Collections TestReferenceMap.java source code

/*
 *  Licensed to the Apache Software Foundation (ASF) under one or more
 *  contributor license agreements.  See the NOTICE file distributed with
 *  this work for additional information regarding copyright ownership.
 *  The ASF licenses this file to You under the Apache License, Version 2.0
 *  (the "License"); you may not use this file except in compliance with
 *  the License.  You may obtain a copy of the License at
 *
 *      http://www.apache.org/licenses/LICENSE-2.0
 *
 *  Unless required by applicable law or agreed to in writing, software
 *  distributed under the License is distributed on an "AS IS" BASIS,
 *  WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 *  See the License for the specific language governing permissions and
 *  limitations under the License.
 */
package org.apache.commons.collections;

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

import junit.framework.Test;

import org.apache.commons.collections.map.AbstractTestMap;

/**
 * Tests for ReferenceMap. 
 * 
 * @version $Revision: 646780 $ $Date: 2008-04-10 13:48:07 +0100 (Thu, 10 Apr 2008) $
 *
 * @author Paul Jack
 * @author Guilhem Lavaux
 */
public class TestReferenceMap extends AbstractTestMap {

    public TestReferenceMap(String testName) {
        super(testName);
    }

    public static Test suite() {
        return BulkTest.makeSuite(TestReferenceMap.class);
    }

    public static void main(String args[]) {
        String[] testCaseName = { TestReferenceMap.class.getName() };
        junit.textui.TestRunner.main(testCaseName);
    }

    public Map makeEmptyMap() {
        ReferenceMap map = new ReferenceMap(ReferenceMap.WEAK, ReferenceMap.WEAK);
        return map;
    }

    public boolean isAllowNullKey() {
        return false;
    }

    public boolean isAllowNullValue() {
        return false;
    }

    public String getCompatibilityVersion() {
        return "2.1";
    }

    //-----------------------------------------------------------------------
    public void testNullHandling() {
        resetFull();
        assertEquals(null, map.get(null));
        assertEquals(false, map.containsKey(null));
        assertEquals(false, map.containsValue(null));
        assertEquals(null, map.remove(null));
        assertEquals(false, map.entrySet().contains(null));
        assertEquals(false, map.keySet().contains(null));
        assertEquals(false, map.values().contains(null));
        try {
            map.put(null, null);
            fail();
        } catch (NullPointerException ex) {}
        try {
            map.put(new Object(), null);
            fail();
        } catch (NullPointerException ex) {}
        try {
            map.put(null, new Object());
            fail();
        } catch (NullPointerException ex) {}
    }

    //-----------------------------------------------------------------------
/*
    // Tests often fail because gc is uncontrollable

    public void testPurge() {
        ReferenceMap map = new ReferenceMap(ReferenceMap.WEAK, ReferenceMap.WEAK);
        Object[] hard = new Object[10];
        for (int i = 0; i < hard.length; i++) {
            hard[i] = new Object();
            map.put(hard[i], new Object());
        }
        gc();
        assertTrue("map should be empty after purge of weak values", map.isEmpty());

        for (int i = 0; i < hard.length; i++) {
            map.put(new Object(), hard[i]);
        }
        gc();
        assertTrue("map should be empty after purge of weak keys", map.isEmpty());

        for (int i = 0; i < hard.length; i++) {
            map.put(new Object(), hard[i]);
            map.put(hard[i], new Object());
        }

        gc();
        assertTrue("map should be empty after purge of weak keys and values", map.isEmpty());
    }


    public void testGetAfterGC() {
        ReferenceMap map = new ReferenceMap(ReferenceMap.WEAK, ReferenceMap.WEAK);
        for (int i = 0; i < 10; i++) {
            map.put(new Integer(i), new Integer(i));
        }

        gc();
        for (int i = 0; i < 10; i++) {
            Integer I = new Integer(i);
            assertTrue("map.containsKey should return false for GC'd element", !map.containsKey(I));
            assertTrue("map.get should return null for GC'd element", map.get(I) == null);
        }
    }


    public void testEntrySetIteratorAfterGC() {
        ReferenceMap map = new ReferenceMap(ReferenceMap.WEAK, ReferenceMap.WEAK);
        Object[] hard = new Object[10];
        for (int i = 0; i < 10; i++) {
            hard[i] = new Integer(10 + i);
            map.put(new Integer(i), new Integer(i));
            map.put(hard[i], hard[i]);
        }

        gc();
        Iterator iterator = map.entrySet().iterator();
        while (iterator.hasNext()) {
            Map.Entry entry = (Map.Entry)iterator.next();
            Integer key = (Integer)entry.getKey();
            Integer value = (Integer)entry.getValue();
            assertTrue("iterator should skip GC'd keys", key.intValue() >= 10);
            assertTrue("iterator should skip GC'd values", value.intValue() >= 10);
        }

    }
*/

    WeakReference keyReference;
    WeakReference valueReference;

    public Map buildRefMap() {
        Object key = new Object();
        Object value = new Object();
        
        keyReference = new WeakReference(key);
        valueReference = new WeakReference(value);
        
        Map testMap = new ReferenceMap(ReferenceMap.WEAK, ReferenceMap.HARD, true);
        testMap.put(key, value);
 
        assertEquals("In map", value, testMap.get(key));
        assertNotNull("Weak reference released early (1)", keyReference.get());
        assertNotNull("Weak reference released early (2)", valueReference.get());
        return testMap;
    }

    /** Tests whether purge values setting works */
    public void testPurgeValues() throws Exception {
        // many thanks to Juozas Baliuka for suggesting this method
      
        Map testMap = buildRefMap();
        
        int iterations = 0;
        int bytz = 2;
        while(true) {
            System.gc();
            if(iterations++ > 50){
                fail("Max iterations reached before resource released.");
            }
            testMap.isEmpty();
            if( 
                keyReference.get() == null &&
                valueReference.get() == null) {
                break;
                
            } else {
                // create garbage:
                byte[] b =  new byte[bytz];
                bytz = bytz * 2;
            }
        }
    }
    
    private static void gc() {
        try {
            // trigger GC
            byte[][] tooLarge = new byte[1000000000][1000000000];
            fail("you have too much RAM");
        } catch (OutOfMemoryError ex) {
            System.gc(); // ignore
        }
    }
}