001    /** 
002     * 
003     * Copyright 2004 Protique Ltd
004     * 
005     * Licensed under the Apache License, Version 2.0 (the "License"); 
006     * you may not use this file except in compliance with the License. 
007     * You may obtain a copy of the License at 
008     * 
009     * http://www.apache.org/licenses/LICENSE-2.0
010     * 
011     * Unless required by applicable law or agreed to in writing, software
012     * distributed under the License is distributed on an "AS IS" BASIS, 
013     * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. 
014     * See the License for the specific language governing permissions and 
015     * limitations under the License. 
016     * 
017     **/
018    package org.activemq.util;
019    
020    import java.util.LinkedHashMap;
021    import java.util.Map;
022    
023    /**
024     * Represnts an LRUCache of a fixed maximum size which by default will
025     * remove items based on access order but can be used to use insertion order
026     *
027     * @version $Revision: 1.1.1.1 $
028     */
029    public class LRUCache extends LinkedHashMap {
030        private static final long serialVersionUID = -5754338187296859149L;
031    
032        protected static final int DEFAULT_INITIAL_CAPACITY = 1000;
033        protected static final float DEFAULT_LOAD_FACTOR = (float) 0.75;
034    
035        private int maxSize;
036    
037        public LRUCache(int initialCapacity, float loadFactor, boolean accessOrder, int maxSize) {
038            super(initialCapacity, loadFactor, accessOrder);
039            this.maxSize = maxSize;
040        }
041    
042        public LRUCache(int maxSize) {
043            this(DEFAULT_INITIAL_CAPACITY, DEFAULT_LOAD_FACTOR, true, maxSize);
044        }
045    
046        public LRUCache(int maxSize, boolean accessOrder) {
047            this(DEFAULT_INITIAL_CAPACITY, DEFAULT_LOAD_FACTOR, accessOrder, maxSize);
048        }
049    
050        protected boolean removeEldestEntry(Map.Entry eldest) {
051            return size() > maxSize;
052        }
053    }