lrucache.java

老外的在线考试

/*
 * Core - Library of useful classes that are used in many CyberDemia projects.
 * Copyright (C) 2003 CyberDemia Research and Services
 *
 * This library is free software; you can redistribute it and/or
 * modify it under the terms of the GNU Library General Public
 * License as published by the Free Software Foundation; either
 * version 2 of the License, or (at your option) any later version.
 *
 * This library is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
 * Library General Public License for more details.
 * 
 * You should have received a copy of the GNU Library General Public
 * License along with this library; if not, write to the
 * Free Software Foundation, Inc., 59 Temple Place - Suite 330,
 * Boston, MA  02111-1307, USA.
 *
 * See the COPYING file located in the top-level-directory of
 * the archive of this library for complete text of license.
 */
package com.cyberdemia.util;

import java.util.*;

/**
* LRUCache is a LRU cache of key-value pairs.
* The maximum number of keys that can be stored (the maxCapacity) is specified in the constructor.
* If the cache is full, a subsequent call to add() will remove the
* least-recently-accessed key-value pair to make room for the new pair.
* LRUCache is a subclass of LinkedHashMap and is not thread-safe.
*
* @author Alexander Yap
* @version $Revision: 1.2 $ at $Date: 2004/02/18 08:35:17 $ by $Author: alexycyap $
*/
public class LRUCache extends LinkedHashMap
{
	/**
	* Creates a LRUCache with default max capacity of 64 and initial capacity of 32.
	*/
	public LRUCache()
	{
		this(32, 64);
	}

	/**
	* Creates a LRUCache.
	* @param initCapacity Initial capacity.
	* @param maxCapacity Maximum number of key-value pairs that can be stored.
	*/
	public LRUCache(int initCapacity, int maxCapacity)
	{
		super(initCapacity, 0.75f, true);
		if (maxCapacity<2)
		{
			throw new IllegalArgumentException("Maximum capacity must be >= 2");
		}
		m_maxSize = maxCapacity;
	}

	protected boolean removeEldestEntry(Map.Entry eldest)
	{
		if ( size()>m_maxSize )
		{
			return true;
		}
		return false;
	}

	protected int m_maxSize;
}