java LRUCache

// Copyright 2007 Christian d'Heureuse, Inventec Informatik AG, Zurich, Switzerland// www.source-code.biz, www.inventec.ch/chdh//// This module is multi-licensed and may be used under the terms// of any of the following licenses:////  EPL, Eclipse Public License, V1.0 or later, http://www.eclipse.org/legal//  LGPL, GNU Lesser General Public License, V2 or later, http://www.gnu.org/licenses/lgpl.html//  GPL, GNU General Public License, V2 or later, http://www.gnu.org/licenses/gpl.html//  AL, Apache License, V2.0 or later, http://www.apache.org/licenses//  BSD, BSD License, http://www.opensource.org/licenses/bsd-license.php//// Please contact the author if you need another license.// This module is provided "as is", without warranties of any kind.import java.util.LinkedHashMap;import java.util.Collection;import java.util.Map;import java.util.ArrayList;/*** An LRU cache, based on <code>LinkedHashMap</code>.** <p>* This cache has a fixed maximum number of elements (<code>cacheSize</code>).* If the cache is full and another entry is added, the LRU (least recently used) entry is dropped.** <p>* This class is thread-safe. All methods of this class are synchronized.** <p>* Author: Christian d'Heureuse, Inventec Informatik AG, Zurich, Switzerland<br>* Multi-licensed: EPL / LGPL / GPL / AL / BSD.*/public class LRUCache<K,V> {private static final float   hashTableLoadFactor = 0.75f;private LinkedHashMap<K,V>   map;private int                  cacheSize;/*** Creates a new LRU cache.* @param cacheSize the maximum number of entries that will be kept in this cache.*/public LRUCache (int cacheSize) {   this.cacheSize = cacheSize;   int hashTableCapacity = (int)Math.ceil(cacheSize / hashTableLoadFactor) + 1;   map = new LinkedHashMap<K,V>(hashTableCapacity, hashTableLoadFactor, true) {      // (an anonymous inner class)      private static final long serialVersionUID = 1;      @Override protected boolean removeEldestEntry (Map.Entry<K,V> eldest) {         return size() > LRUCache.this.cacheSize; }}; }/*** Retrieves an entry from the cache.<br>* The retrieved entry becomes the MRU (most recently used) entry.* @param key the key whose associated value is to be returned.* @return    the value associated to this key, or null if no value with this key exists in the cache.*/public synchronized V get (K key) {   return map.get(key); }/*** Adds an entry to this cache.* The new entry becomes the MRU (most recently used) entry.* If an entry with the specified key already exists in the cache, it is replaced by the new entry.* If the cache is full, the LRU (least recently used) entry is removed from the cache.* @param key    the key with which the specified value is to be associated.* @param value  a value to be associated with the specified key.*/public synchronized void put (K key, V value) {   map.put (key, value); }/*** Clears the cache.*/public synchronized void clear() {   map.clear(); }/*** Returns the number of used entries in the cache.* @return the number of entries currently in the cache.*/public synchronized int usedEntries() {   return map.size(); }/*** Returns a <code>Collection</code> that contains a copy of all cache entries.* @return a <code>Collection</code> with a copy of the cache content.*/public synchronized Collection<Map.Entry<K,V>> getAll() {   return new ArrayList<Map.Entry<K,V>>(map.entrySet()); }} // end class LRUCache