MostRecentlyUsedMap.java Source code

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Here is the source code for MostRecentlyUsedMap.java

Source

/*
 * $Id: MostRecentlyUsedMap.java 457812 2005-10-06 21:20:34Z jdonnerstag $
 * $Revision: 457812 $ $Date: 2005-10-06 23:20:34 +0200 (Thu, 06 Oct 2005) $
 * 
 * 
 * Licensed 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.
 */

import java.util.LinkedHashMap;
import java.util.Map;

/**
 * Holds a map of most recently used items of a given maximum size. Old entries
 * are expired when the map exceeds that maximum size.
 * 
 * @author Jonathan Locke
 */
public class MostRecentlyUsedMap extends LinkedHashMap {
    private static final long serialVersionUID = 1L;

    /** Value most recently removed from map */
    Object removedValue;

    /** Maximum number of entries allowed in this map */
    private int maxEntries;

    /**
     * Constructor
     *  
     * @param maxEntries
     *            Maximum number of entries allowed in the map
     */
    public MostRecentlyUsedMap(final int maxEntries) {
        super(10, 0.75f, true);

        if (maxEntries <= 0) {
            throw new IllegalArgumentException("Must have at least one entry");
        }

        this.maxEntries = maxEntries;
    }

    /**
     * @return Returns the removedValue.
     */
    public Object getRemovedValue() {
        return removedValue;
    }

    /**
     * @see java.util.LinkedHashMap#removeEldestEntry(java.util.Map.Entry)
     */
    protected boolean removeEldestEntry(final Map.Entry eldest) {
        final boolean remove = size() > maxEntries;
        // when it should be removed remember the oldest value that will be removed
        if (remove) {
            this.removedValue = eldest.getValue();
        } else {
            removedValue = null;
        }
        return remove;
    }
}