001 /*--------------------------------------------------------------------------+ 002 $Id: LRUCacheBase.java 26268 2010-02-18 10:44:30Z juergens $ 003 | | 004 | Copyright 2005-2010 Technische Universitaet Muenchen | 005 | | 006 | Licensed under the Apache License, Version 2.0 (the "License"); | 007 | you may not use this file except in compliance with the License. | 008 | You may obtain a copy of the License at | 009 | | 010 | http://www.apache.org/licenses/LICENSE-2.0 | 011 | | 012 | Unless required by applicable law or agreed to in writing, software | 013 | distributed under the License is distributed on an "AS IS" BASIS, | 014 | WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. | 015 | See the License for the specific language governing permissions and | 016 | limitations under the License. | 017 +--------------------------------------------------------------------------*/ 018 package edu.tum.cs.commons.cache; 019 020 import java.util.LinkedHashMap; 021 022 import edu.tum.cs.commons.assertion.CCSMPre; 023 import edu.tum.cs.commons.error.NeverThrownRuntimeException; 024 025 /** 026 * A cache with a fixed size using a last recently used (LRU) strategy. If 027 * identifiers itself are suitable hash keys, use class 028 * {@link edu.tum.cs.commons.cache.LRUStraightCacheBase}. 029 * 030 * @author hummelb 031 * @author $Author: juergens $ 032 * @version $Rev: 26268 $ 033 * @levd.rating GREEN Hash: 7C20602D714E70624D8FF1B0F6BAAEFF 034 * 035 * @param <I> 036 * the index type of the cache 037 * @param <H> 038 * the hash map key type 039 * @param <E> 040 * the type stored in the cache 041 * @param <X> 042 * the type of exception thrown by the {@link #obtainItem(Object)} 043 * method. Use the {@link NeverThrownRuntimeException} if no 044 * exception will be thrown. 045 */ 046 public abstract class LRUCacheBase<I, H, E, X extends Exception> extends 047 CacheBase<I, H, E, X> { 048 049 /** The actual cache. */ 050 private final LinkedHashMap<H, E> cache; 051 052 /** Constructor. */ 053 public LRUCacheBase(final int maxSize) { 054 CCSMPre.isTrue(maxSize > 0, "Maximal size must be positive!"); 055 056 cache = new LinkedHashMap<H, E>(2 * maxSize, .6f, true) { 057 @Override 058 protected boolean removeEldestEntry(java.util.Map.Entry<H, E> eldest) { 059 return size() > maxSize; 060 } 061 }; 062 } 063 064 /** {@inheritDoc} */ 065 @Override 066 public E getItem(I identifier) throws X { 067 H key = getHashKey(identifier); 068 E value = cache.get(key); 069 if (value == null) { 070 value = obtainItem(identifier); 071 cache.put(key, value); 072 } 073 return value; 074 } 075 }