org.apache.oro.util.CacheLRU Maven / Gradle / Ivy
/*
* $Id: CacheLRU.java,v 1.10 2003/11/07 20:16:25 dfs Exp $
*
* ====================================================================
* The Apache Software License, Version 1.1
*
* Copyright (c) 2000 The Apache Software Foundation. All rights
* reserved.
*
* Redistribution and use in source and binary forms, with or without
* modification, are permitted provided that the following conditions
* are met:
*
* 1. Redistributions of source code must retain the above copyright
* notice, this list of conditions and the following disclaimer.
*
* 2. Redistributions in binary form must reproduce the above copyright
* notice, this list of conditions and the following disclaimer in
* the documentation and/or other materials provided with the
* distribution.
*
* 3. The end-user documentation included with the redistribution,
* if any, must include the following acknowledgment:
* "This product includes software developed by the
* Apache Software Foundation (http://www.apache.org/)."
* Alternately, this acknowledgment may appear in the software itself,
* if and wherever such third-party acknowledgments normally appear.
*
* 4. The names "Apache" and "Apache Software Foundation", "Jakarta-Oro"
* must not be used to endorse or promote products derived from this
* software without prior written permission. For written
* permission, please contact [email protected].
*
* 5. Products derived from this software may not be called "Apache"
* or "Jakarta-Oro", nor may "Apache" or "Jakarta-Oro" appear in their
* name, without prior written permission of the Apache Software Foundation.
*
* THIS SOFTWARE IS PROVIDED ``AS IS'' AND ANY EXPRESSED OR IMPLIED
* WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
* OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
* DISCLAIMED. IN NO EVENT SHALL THE APACHE SOFTWARE FOUNDATION OR
* ITS CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
* SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
* LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF
* USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND
* ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
* OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT
* OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
* SUCH DAMAGE.
* ====================================================================
*
* This software consists of voluntary contributions made by many
* individuals on behalf of the Apache Software Foundation. For more
* information on the Apache Software Foundation, please see
*
* @param capacity The capacity of the cache.
*/
public CacheLRU(int capacity) {
super(capacity);
int i;
__next = new int[_cache.length];
__prev = new int[_cache.length];
for(i=0; i < __next.length; i++)
__next[i] = __prev[i] = -1;
}
/**
* Same as:
*
* CacheLRU(GenericCache.DEFAULT_CAPACITY);
*
*/
public CacheLRU(){
this(GenericCache.DEFAULT_CAPACITY);
}
private void __moveToFront(int index) {
int next, prev;
if(__head != index) {
next = __next[index];
prev = __prev[index];
// Only the head has a prev entry that is an invalid index so
// we don't check.
__next[prev] = next;
// Make sure index is valid. If it isn't, we're at the tail
// and don't set __prev[next].
if(next >= 0)
__prev[next] = prev;
else
__tail = prev;
__prev[index] = -1;
__next[index] = __head;
__prev[__head] = index;
__head = index;
}
}
public synchronized Object getElement(Object key) {
Object obj;
obj = _table.get(key);
if(obj != null) {
GenericCacheEntry entry;
entry = (GenericCacheEntry)obj;
// Maintain LRU property
__moveToFront(entry._index);
return entry._value;
}
return null;
}
/**
* Adds a value to the cache. If the cache is full, when a new value
* is added to the cache, it replaces the least recently used value
* in the cache (i.e., LRU).
*
* @param key The key referencing the value added to the cache.
* @param value The value to add to the cache.
*/
public final synchronized void addElement(Object key, Object value) {
Object obj;
obj = _table.get(key);
if(obj != null) {
GenericCacheEntry entry;
// Just replace the value, but move it to the front.
entry = (GenericCacheEntry)obj;
entry._value = value;
entry._key = key;
__moveToFront(entry._index);
return;
}
// If we haven't filled the cache yet, place in next available spot
// and move to front.
if(!isFull()) {
if(_numEntries > 0) {
__prev[_numEntries] = __tail;
__next[_numEntries] = -1;
__moveToFront(_numEntries);
}
++_numEntries;
} else {
// We replace the tail of the list.
_table.remove(_cache[__tail]._key);
__moveToFront(__tail);
}
_cache[__head]._value = value;
_cache[__head]._key = key;
_table.put(key, _cache[__head]);
}
}