org.intermine.util.SoftReferenceMap Maven / Gradle / Ivy

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package org.intermine.util;

/*
 * Copyright (C) 2002-2022 FlyMine
 *
 * This code may be freely distributed and modified under the
 * terms of the GNU Lesser General Public Licence.  This should
 * be distributed with the code.  See the LICENSE file for more
 * information or http://www.gnu.org/copyleft/lesser.html.
 *
 */

import java.lang.ref.ReferenceQueue;
import java.lang.ref.SoftReference;

/**
 * This is a Map implementation designed specifically for people intending to create a cache.
 * The keys are held strongly, but the values are held softly, so the values can be
 * garbage-collected. When an entry is garbage-collected, its key is removed from the Map on
 * the next Map activity. Subclasses of this map are required to provide the actual Map
 * functionality.
 * 
 * The entrySet() and values() methods of this class do not work.
 *
 * @see java.lang.ref.SoftReference
 * @param  the type of keys maintained by this map
 * @param  the type of mapped values
 * @author Matthew Wakeling
 */
public abstract class SoftReferenceMap extends ReferenceMap
{
    /**
     * Returns a new SoftReferenceWithKey object for the given objects.
     *
     * @param value an Object
     * @param queue a ReferenceQueue
     * @param key an Object
     * @return a SoftReferenceWithKey object
     */
    @Override
    protected SoftReferenceWithKey newRef(Object value, ReferenceQueue