Mega Code Archive
Generic LRU Cache
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/*
* Licensed to the Apache Software Foundation (ASF) under one or more
* contributor license agreements. See the NOTICE file distributed with
* this work for additional information regarding copyright ownership.
* The ASF licenses this file to You under the Apache License, Version 2.0
* (the "License"); you may not use this file except in compliance with
* the License. You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/
import java.util.Hashtable;
/**
* This class implements a Generic LRU Cache
*
* @author Ignacio J. Ortega
*
*/
public class LRUCache
{
class CacheNode
{
CacheNode prev;
CacheNode next;
Object value;
Object key;
CacheNode()
{
}
}
public LRUCache(int i)
{
currentSize = 0;
cacheSize = i;
nodes = new Hashtable(i);
}
public Object get(Object key)
{
CacheNode node = (CacheNode)nodes.get(key);
if(node != null)
{
moveToHead(node);
return node.value;
}
else
{
return null;
}
}
public void put(Object key, Object value)
{
CacheNode node = (CacheNode)nodes.get(key);
if(node == null)
{
if(currentSize >= cacheSize)
{
if(last != null)
nodes.remove(last.key);
removeLast();
}
else
{
currentSize++;
}
node = new CacheNode();
}
node.value = value;
node.key = key;
moveToHead(node);
nodes.put(key, node);
}
public Object remove(Object key) {
CacheNode node = (CacheNode)nodes.get(key);
if (node != null) {
if (node.prev != null) {
node.prev.next = node.next;
}
if (node.next != null) {
node.next.prev = node.prev;
}
if (last == node)
last = node.prev;
if (first == node)
first = node.next;
}
return node;
}
public void clear()
{
first = null;
last = null;
}
private void removeLast()
{
if(last != null)
{
if(last.prev != null)
last.prev.next = null;
else
first = null;
last = last.prev;
}
}
private void moveToHead(CacheNode node)
{
if(node == first)
return;
if(node.prev != null)
node.prev.next = node.next;
if(node.next != null)
node.next.prev = node.prev;
if(last == node)
last = node.prev;
if(first != null)
{
node.next = first;
first.prev = node;
}
first = node;
node.prev = null;
if(last == null)
last = first;
}
private int cacheSize;
private Hashtable nodes;
private int currentSize;
private CacheNode first;
private CacheNode last;
}
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