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package com.jme3.terrain.geomipmap;
// Copyright 2007 Christian d'Heureuse, Inventec Informatik AG, Zurich,
// Switzerland
// www.source-code.biz, www.inventec.ch/chdh
//
// This module is multi-licensed and may be used under the terms
// of any of the following licenses:
//
// EPL, Eclipse Public License, V1.0 or later, http://www.eclipse.org/legal
// LGPL, GNU Lesser General Public License, V2 or later,
// http://www.gnu.org/licenses/lgpl.html
// GPL, GNU General Public License, V2 or later,
// http://www.gnu.org/licenses/gpl.html
// AL, Apache License, V2.0 or later, http://www.apache.org/licenses
// BSD, BSD License, http://www.opensource.org/licenses/bsd-license.php
//
// Please contact the author if you need another license.
// This module is provided "as is", without warranties of any kind.
import java.util.ArrayList;
import java.util.Collection;
import java.util.LinkedHashMap;
import java.util.Map;
/**
* An LRU cache, based on <code>LinkedHashMap</code>.
*
* <p>
* This cache has a fixed maximum number of elements (<code>cacheSize</code>).
* If the cache is full and another entry is added, the LRU (least recently
* used) entry is dropped.
*
* <p>
* This class is thread-safe. All methods of this class are synchronized.
*
* <p>
* Author: Christian d'Heureuse, Inventec Informatik AG, Zurich, Switzerland<br>
* Multi-licensed: EPL / LGPL / GPL / AL / BSD.
*/
public class LRUCache<K, V> {
private static final float hashTableLoadFactor = 0.75f;
private LinkedHashMap<K, V> map;
private int cacheSize;
/**
* Creates a new LRU cache.
*
* @param cacheSize
* the maximum number of entries that will be kept in this cache.
*/
public LRUCache(int cacheSize) {
this.cacheSize = cacheSize;
int hashTableCapacity = (int) Math.ceil(cacheSize / LRUCache.hashTableLoadFactor) + 1;
this.map = new LinkedHashMap<K, V>(hashTableCapacity, LRUCache.hashTableLoadFactor, true) {
// (an anonymous inner class)
private static final long serialVersionUID = 1;
@Override
protected boolean removeEldestEntry(Map.Entry<K, V> eldest) {
return this.size() > LRUCache.this.cacheSize;
}
};
}
/**
* Retrieves an entry from the cache.<br>
* The retrieved entry becomes the MRU (most recently used) entry.
*
* @param key
* the key whose associated value is to be returned.
* @return the value associated to this key, or null if no value with this
* key exists in the cache.
*/
public synchronized V get(K key) {
return this.map.get(key);
}
/**
* Adds an entry to this cache.
* The new entry becomes the MRU (most recently used) entry.
* If an entry with the specified key already exists in the cache, it is
* replaced by the new entry.
* If the cache is full, the LRU (least recently used) entry is removed from
* the cache.
*
* @param key
* the key with which the specified value is to be associated.
* @param value
* a value to be associated with the specified key.
*/
public synchronized void put(K key, V value) {
this.map.put(key, value);
}
/**
* Clears the cache.
*/
public synchronized void clear() {
this.map.clear();
}
/**
* Returns the number of used entries in the cache.
*
* @return the number of entries currently in the cache.
*/
public synchronized int usedEntries() {
return this.map.size();
}
/**
* Returns a <code>Collection</code> that contains a copy of all cache
* entries.
*
* @return a <code>Collection</code> with a copy of the cache content.
*/
public synchronized Collection<Map.Entry<K, V>> getAll() {
return new ArrayList<Map.Entry<K, V>>(this.map.entrySet());
}
} // end class LRUCache
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