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/*
========== licence begin GPL
Copyright (C) 2002-2003 SAP AG
This program is free software; you can redistribute it and/or
modify it under the terms of the GNU General Public License
as published by the Free Software Foundation; either version 2
of the License, or (at your option) any later version.
This program 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 General Public License for more details.
You should have received a copy of the GNU General Public License
along with this program; if not, write to the Free Software
Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA.
========== licence end
*/
package com.sap.dbtech.util.cache;
import java.util.*;
/**
*
*/
public class LruCache
{
/**
*
*/
private static class Association
extends DListElement
{
Object key;
Association (
Object key,
Object value)
{
super (value);
this.key = key;
}
final Object getKey ()
{
return this.key;
}
}
private Dictionary lookup;
private Association lruTop;
private Association lruBottom;
private int currentSize;
private int maxSize;
static Object[] templateForClear=new Object[0];
/**
* creates a new LruCache
*/
public
LruCache (
int cacheSize)
{
this.maxSize = cacheSize;
this.clear ();
}
/**
*
*/
public void
clear ()
{
this.currentSize = 0;
this.lookup = new Hashtable (this.maxSize);
this.lruTop = null;
this.lruBottom = null;
}
/**
*
*/
public Object
get (
Object key)
{
Object result = null;
Association entry;
entry = (Association) this.lookup.get (key);
if (entry != null) {
result = entry.getObject ();
this.moveToTop (entry);
}
return result;
}
/**
*
*/
public void
put (
Object key,
Object value)
{
Association newEntry = new Association (key, value);
this.lookup.put (key, newEntry);
if (this.lruTop != null) {
this.lruTop.prepend (newEntry);
}
this.lruTop = newEntry;
if (this.lruBottom == null) {
this.lruBottom = newEntry;
}
++this.currentSize;
if (this.currentSize > this.maxSize) {
this.removeLast ();
}
}
/**
*
*/
private void
moveToTop (
Association entry)
{
if (entry == this.lruTop) {
return;
}
if (entry == this.lruBottom) {
this.lruBottom = (Association) entry.previous ();
}
entry.remove ();
this.lruTop.prepend (entry);
this.lruTop = entry;
}
/**
*
*/
private void
removeLast ()
{
Association toDelete = this.lruBottom;
this.lruBottom = (Association) toDelete.previous ();
this.lookup.remove(toDelete.getKey ());
this.removeHook (toDelete);
--this.currentSize;
}
/**
*
*/
protected void
removeHook (
Object value)
{
}
/**
* Returns all values and afterwards clears this cache.
* @return an array of the stored <i>values</i>.
*/
public Object[] clearAll()
{
Object[] result=((Hashtable)lookup).values().toArray(templateForClear);
clear();
return result;
}
}
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