org.apache.hadoop.util.LRUCache Maven / Gradle / Ivy
/**
* Licensed to the Apache Software Foundation (ASF) under one
* or more contributor license agreements. See the NOTICE file
* distributed with this work for additional information
* regarding copyright ownership. The ASF licenses this file
* to you under the Apache License, Version 2.0 (the
* "License"); you may not use this file except in compliance
* with the License. You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/
package org.apache.hadoop.util;
import java.util.LinkedHashMap;
import java.util.Map;
public class LRUCache {
private static final float hashTableLoadFactor = 0.75f;
private LinkedHashMap map;
private int cacheSize;
/**
* Creates a new LRU cache.
* @param cacheSize the maximum number of entries in this cache.
*/
public LRUCache(int cacheSize) {
this.cacheSize = cacheSize;
int hashTableCapacity = (int)Math.ceil(cacheSize / hashTableLoadFactor) + 1;
map = new LinkedHashMap(hashTableCapacity, hashTableLoadFactor, true) {
private static final long serialVersionUID = 1;
@Override
protected boolean removeEldestEntry (Map.Entry eldest) {
return size() > LRUCache.this.cacheSize; }};
}
/**
* Retrieves an entry from the cache.
* The retrieved entry becomes the 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 map.get(key);
}
/**
* Adds an entry to this cache.
* The new entry becomes the 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) {
map.put(key, value);
}
/**
* Remove an entry from this cache.
* If an entry with the specified key already exists in the cache, it is removed.
* If the entry does not exist, then null is returned.
* @param key the key with which the specified value is to be associated.
* @param value the value that was associated with the specified key, null otherwise.
*/
public synchronized V remove(K key) {
return map.remove(key);
}
/**
* Empty the cache.
*/
public synchronized void clear() {
map.clear();
}
/**
* Returns the current size of the cache.
* @return the number of entries currently in the cache.
*/
public synchronized int size() {
return map.size();
}
}