001 /******************************************************************************* 002 * Portions created by Sebastian Thomschke are copyright (c) 2005-2011 Sebastian 003 * Thomschke. 004 * 005 * All Rights Reserved. This program and the accompanying materials 006 * are made available under the terms of the Eclipse Public License v1.0 007 * which accompanies this distribution, and is available at 008 * http://www.eclipse.org/legal/epl-v10.html 009 * 010 * Contributors: 011 * Sebastian Thomschke - initial implementation. 012 *******************************************************************************/ 013 package net.sf.oval.internal.util; 014 015 import java.lang.ref.SoftReference; 016 import java.util.HashMap; 017 import java.util.LinkedList; 018 import java.util.Map; 019 020 /** 021 * @author Sebastian Thomschke 022 */ 023 public final class ObjectCache<K, V> 024 { 025 private final Map<K, SoftReference<V>> map = new HashMap<K, SoftReference<V>>(); 026 027 private final LinkedList<V> objectsLastAccessed = new LinkedList<V>(); 028 private final int objectsToKeepCount; 029 030 /** 031 * Creates a new cache keeping all objects. 032 */ 033 public ObjectCache() 034 { 035 objectsToKeepCount = -1; 036 } 037 038 /** 039 * @param maxObjectsToKeep the number of cached objects that should stay in memory when GC 040 * starts removing SoftReferences to free memory 041 */ 042 public ObjectCache(final int maxObjectsToKeep) 043 { 044 this.objectsToKeepCount = maxObjectsToKeep; 045 } 046 047 public void compact() 048 { 049 for (final Map.Entry<K, SoftReference<V>> entry : map.entrySet()) 050 { 051 final SoftReference<V> ref = entry.getValue(); 052 if (ref.get() == null) map.remove(entry.getKey()); 053 } 054 } 055 056 public boolean contains(final K key) 057 { 058 return map.containsKey(key); 059 } 060 061 public V get(final K key) 062 { 063 final SoftReference<V> softReference = map.get(key); 064 if (softReference != null) 065 { 066 final V value = softReference.get(); 067 068 if (value == null) 069 map.remove(key); 070 else if (objectsToKeepCount > 0 && value != objectsLastAccessed.getFirst()) 071 { 072 objectsLastAccessed.remove(value); 073 objectsLastAccessed.addFirst(value); 074 if (objectsLastAccessed.size() > objectsToKeepCount) objectsLastAccessed.removeLast(); 075 } 076 return softReference.get(); 077 } 078 return null; 079 } 080 081 public void put(final K key, final V value) 082 { 083 map.remove(key); 084 map.put(key, new SoftReference<V>(value)); 085 } 086 }