LRU算法简单例子
转：http://blog.csdn.net/5iasp/article/details/4268090
package com.aspboy.base.cache;
/*
* Created on 2004-8-18
*
*“最近最少使用算法”（LRU算法），它是将最近一段时间内最少被访问过的行淘汰出局。
*因此需要为每行设置一个计数器，LRU算法是把命中行的计数器清零，其他各行计数器加1。
*当需要替换时淘汰行计数器计数值最大的数据行出局。
*这是一种高效、科学的算法，其计数器清零过程可以把一些频繁调用后再不需要的数据淘汰出Cache，
*提高Cache的利用率。
*/
import java.util.HashMap;
import java.util.Iterator;
import java.util.Set;
/**
* @author 刘跃清
*
* 最近最少使用算法 Window - Preferences - Java - Code Style - Code Templates
*/
public class LRU
{
protected HashMap lruCache = new HashMap(2);
//可操作的最大使用次数
protected int MAX_INTEGER_NUMBER=2147483647;
//缓存中保存的数大对象数目
protected int max_object_num=1000;
public LRU()
{
}
public LRU(int maxObjectNum)
{
max_object_num=maxObjectNum;
}
/**
* 增加对象到缓存中
* @param key
* @param value
*/
public Object put(Object key, Object value)
{
CacheObject newValue = new CacheObject(value);
if (lruCache.size()>=max_object_num)
{
removeLease();
}
return lruCache.put(key, newValue);
}
/**
* 使用key来获取对象
*
* @param key
* @return
*/
public Object get(Object key)
{
CacheObject object=(CacheObject)lruCache.get(key);
if (object==null)
{
return null;
}
//根据LRU算法原则，将命中的对象计算器0，将其他对象的计算值加1
Set set=lruCache.keySet();
Iterator iter=set.iterator();
Object keyObject=null;
CacheObject cacheObject=null;
while(iter.hasNext())
{
keyObject=iter.next();
cacheObject=(CacheObject) lruCache.get(keyObject);
cacheObject.setUsetimes(cacheObject.getUsetimes()+1);
}
object.setUsetimes(0);
return object!=null? object.getValue():null;
}
public boolean containsKey(Object key)
{
return lruCache.containsKey(key);
}
public void clear()
{
lruCache.clear();
}
public int size()
{
return lruCache.size();
}
public boolean isEmpty()
{
return lruCache.isEmpty();
}
public boolean containsValue(Object value)
{
return lruCache.containsKey(value);
}
/**
* 移除使用最少的对象
*/
public void removeLease()
{
Object leaseUseObjectKey=null;
int usetimes=0;
Set set=lruCache.keySet();
Iterator iter=set.iterator();
while(iter.hasNext())
{
Object keyObject=iter.next();
CacheObject object=(CacheObject) lruCache.get(keyObject);
if (object.getUsetimes()>usetimes)
{
usetimes=object.getUsetimes();
leaseUseObjectKey=keyObject;
}
}
lruCache.remove(leaseUseObjectKey);
}
public Set keySet()
{
return lruCache.keySet();
}
/**
* 移除使用最频繁的对象
*/
public void removeMost()
{
Object leaseUseObjectKey=null;
int usetimes=MAX_INTEGER_NUMBER;
Set set=lruCache.keySet();
Iterator iter=set.iterator();
while(iter.hasNext())
{
Object keyObject=iter.next();
CacheObject object=(CacheObject) lruCache.get(keyObject);
if (object.getUsetimes()<usetimes)
{
usetimes=object.getUsetimes();
leaseUseObjectKey=keyObject;
}
}
lruCache.remove(leaseUseObjectKey);
}
/**
* 移除最早置入缓存的对象
*/
public void removeEarly()
{
Object leaseUseObjectKey=null;
long time=System.currentTimeMillis()+365*24*60*60*1000;
Set set=lruCache.keySet();
Iterator iter=set.iterator();
while(iter.hasNext())
{
Object keyObject=iter.next();
CacheObject object=(CacheObject) lruCache.get(keyObject);
if (object.getPushtime()<time)
{
time=object.getPushtime();
leaseUseObjectKey=keyObject;
}
}
lruCache.remove(leaseUseObjectKey);
}
/**
* 移除最迟放入的对象
*/
public void removeLater()
{
Object leaseUseObjectKey=null;
long time=-1;
Set set=lruCache.keySet();
Iterator iter=set.iterator();
while(iter.hasNext())
{
Object keyObject=iter.next();
CacheObject object=(CacheObject) lruCache.get(keyObject);
if (object.getPushtime()>time)
{
time=object.getPushtime();
leaseUseObjectKey=keyObject;
}
}
lruCache.remove(leaseUseObjectKey);
}
/**
* 删除某个键值及对应对象
* @param key
*/
public void remove(Object key)
{
lruCache.remove(key);
}
public static void main(String[] args)
{
LRU lru = new LRU(4);
lru.put("a","The A String");
lru.put("b","The B String");
lru.put("d","The D String");
lru.put("c","The C String");
System.out.println(lru.toString());
lru.get("a");
lru.get("b");
lru.get("d");
lru.get("a");
lru.get("b");
lru.get("d");
lru.put("e","The E String");
lru.get("e");
lru.get("e");
lru.get("e");
lru.get("e");
System.out.println(lru.toString());
}
public String toString()
{
StringBuffer strBf= new StringBuffer(10);
Set set1=lruCache.keySet();
Iterator iter1=set1.iterator();
while(iter1.hasNext())
{
Object key=iter1.next();
strBf.append(key+"=");
strBf.append(lruCache.get(key));
strBf.append("/n");
}
return strBf.toString();
}
}
package com.aspboy.base.cache;
/*
* Created on 2004-9-7
*
* TODO To change the template for this generated file go to
* Window - Preferences - Java - Code Style - Code Templates
*/
/**
*
* TODO To change the template for this generated type comment go to
* Window - Preferences - Java - Code Style - Code Templates
*/
public class CacheObject
{
long pushtime = 0;
int usetimes = 0;
Object value = null;
CacheObject( Object value )
{
pushtime = System.currentTimeMillis();
usetimes = 0;
this.value = value;
}
/**
* @return Returns the pushtime.
*/
public final long getPushtime()
{
return pushtime;
}
/**
* @return Returns the usetimes.
*/
public final int getUsetimes()
{
return usetimes;
}
/**
* @param usetimes The usetimes to set.
*/
public final void setUsetimes(int usetimes)
{
this.usetimes = usetimes;
}
/**
* @return Returns the value.
*/
public final Object getValue()
{
return value;
}
/**
* @param value The value to set.
*/
public final void setValue(Object value)
{
this.value = value;
}
public String toString()
{
StringBuffer strBf=new StringBuffer(10);
strBf.append("value="+value+'/n');
strBf.append("pushtime="+pushtime+'/n');
strBf.append("usetimes="+usetimes+'/n');
return strBf.toString();
}
}