001    /**
002     * Licensed to the Apache Software Foundation (ASF) under one or more
003     * contributor license agreements.  See the NOTICE file distributed with
004     * this work for additional information regarding copyright ownership.
005     * The ASF licenses this file to You under the Apache License, Version 2.0
006     * (the "License"); you may not use this file except in compliance with
007     * the License.  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    package org.apache.activemq.memory;
018    
019    import java.util.LinkedHashMap;
020    import java.util.Map;
021    
022    /**
023     * A simple least-recently-used cache of a fixed size.
024     * 
025     * 
026     */
027    public class LRUMap<K,V> extends LinkedHashMap<K,V>{
028    
029        protected static final float DEFAULT_LOAD_FACTOR = (float) 0.75;
030        protected static final int DEFAULT_INITIAL_CAPACITY = 5000;
031        private static final long serialVersionUID = -9179676638408888162L;
032    
033        private int maximumSize;
034    
035        public LRUMap(int maximumSize) {
036            this(DEFAULT_INITIAL_CAPACITY, DEFAULT_LOAD_FACTOR, true, maximumSize);
037        }
038    
039        public LRUMap(int maximumSize, boolean accessOrder) {
040            this(DEFAULT_INITIAL_CAPACITY, DEFAULT_LOAD_FACTOR, accessOrder, maximumSize);
041        }
042    
043        public LRUMap(int initialCapacity, float loadFactor, boolean accessOrder, int maximumSize) {
044            super(initialCapacity, loadFactor, accessOrder);
045            this.maximumSize = maximumSize;
046        }
047    
048        protected boolean removeEldestEntry(Map.Entry<K,V> eldest) {
049            return size() > maximumSize;
050        }
051    }