Simple Example of LRU Algorithm

Package com. aspboy. Base. cache;

/*
* Created on 2004-
*
* The "least recently used algorithm" (LRU algorithm) removes the rows that have been least accessed in the recent period.
* Therefore, you must set a counter for each row. The LRU algorithm clears the counters of hit rows and Adds 1 to the counters of other rows.
* If a replacement is required, the data row with the highest counter count is eliminated.
* This is an efficient and scientific algorithm. In the counter clearing process, you can remove unnecessary data from the cache after frequent calls,
* Improves the cache utilization.
*/

Import java. util. hashmap;
Import java. util. iterator;
Import java. util. Set;

/**
* @ Author Liu Yueqing
*
* Recently, the minimum algorithm window-preferences-Java-code style-code templates is used.
*/
Public class LRU
{
Protected hashmap lrucache = new hashmap (2 );

// Maximum number of operable Use Times
Protected int MAX_INTEGER_NUMBER = 2147483647;

// Number of objects saved in the cache
Protected int max_object_num= 1000;

Public LRU ()
{
}

Public LRU (int maxObjectNum)
{
Max_object_num = maxObjectNum;
}

/**
* Add an object to the cache.
* @ Param key
* @ Param value
*/
Public Object put (Object key, Object value)
{
CacheObject newValue = new CacheObject (value );
If (lruCache. size ()> = max_object_num)
{
Removel.pdf ();
}

Return lruCache. put (key, newValue );
}

/**
* Use the key to get the object
*
* @ Param key
* @ Return
*/
Public Object get (Object key)
{
CacheObject object = (CacheObject) lruCache. get (key );
If (object = null)
{
Return null;
}

// Based on the LRU algorithm principle, add the hit object calculator 0 and the calculation value of other objects to 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 );
}

/**
* Remove objects that use the least amount of data
*/
Public void removel.pdf ()
{
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 ();
}
/**
* Remove objects that are most frequently used
*/
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 );
}

/**
* Remove the first cached object
*/
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 );
}

/**
* Remove the latest object.
*/
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 );
}

/**
* Delete A key value and corresponding object
* @ 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 ("");
LRU. Get ("B ");
LRU. Get ("D ");
LRU. Get ("");
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
* Window-Preferences-Java-Code Style-Code Templates
*/
/**

*
* TODO To change the template for this generated type comment go
* 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 ();
}
}