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.fusesource.hawtdb.util;
018    
019    import java.util.LinkedHashMap;
020    import java.util.Map;
021    
022    /**
023     * A Simple LRU Cache
024     * 
025     * @param <K>
026     * @param <V>
027     */
028    
029    public class LRUCache<K, V> extends LinkedHashMap<K, V> {
030        private static final long serialVersionUID = -342098639681884413L;
031        protected int maxCacheSize = 10000;
032    
033        /**
034         * Default constructor for an LRU Cache The default capacity is 10000
035         */
036        public LRUCache() {
037            this(0,10000, 0.75f, true);
038        }
039    
040        /**
041         * Constructs a LRUCache with a maximum capacity
042         * 
043         * @param maximumCacheSize
044         */
045        public LRUCache(int maximumCacheSize) {
046            this(0, maximumCacheSize, 0.75f, true);
047        }
048    
049        /**
050         * Constructs an empty <tt>LRUCache</tt> instance with the specified
051         * initial capacity, maximumCacheSize,load factor and ordering mode.
052         * 
053         * @param initialCapacity the initial capacity.
054         * @param maximumCacheSize
055         * @param loadFactor the load factor.
056         * @param accessOrder the ordering mode - <tt>true</tt> for access-order,
057         *                <tt>false</tt> for insertion-order.
058         * @throws IllegalArgumentException if the initial capacity is negative or
059         *                 the load factor is non-positive.
060         */
061    
062        public LRUCache(int initialCapacity, int maximumCacheSize, float loadFactor, boolean accessOrder) {
063            super(initialCapacity, loadFactor, accessOrder);
064            this.maxCacheSize = maximumCacheSize;
065        }
066    
067        /**
068         * @return Returns the maxCacheSize.
069         */
070        public int getMaxCacheSize() {
071            return maxCacheSize;
072        }
073    
074        /**
075         * @param maxCacheSize The maxCacheSize to set.
076         */
077        public void setMaxCacheSize(int maxCacheSize) {
078            this.maxCacheSize = maxCacheSize;
079        }
080    
081        protected boolean removeEldestEntry(Map.Entry<K,V> eldest) {
082            return size() > maxCacheSize;
083        }
084    }