001/*
002 * Cache.java July 2006
003 *
004 * Copyright (C) 2006, Niall Gallagher <niallg@users.sf.net>
005 *
006 * Licensed under the Apache License, Version 2.0 (the "License");
007 * you may not use this file except in compliance with the License.
008 * You may obtain a copy of the License at
009 *
010 *     http://www.apache.org/licenses/LICENSE-2.0
011 *
012 * Unless required by applicable law or agreed to in writing, software
013 * distributed under the License is distributed on an "AS IS" BASIS,
014 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or 
015 * implied. See the License for the specific language governing 
016 * permissions and limitations under the License.
017 */
018
019package org.simpleframework.xml.util;
020
021/**
022 * The <code>Cache</code> interface is used to represent a cache
023 * that will store key value pairs. The cache exposes only several
024 * methods to ensure that implementations can focus on performance
025 * concerns rather than how to manage the cached values.
026 * 
027 * @author Niall Gallagher
028 */
029public interface Cache<T> {
030   
031   /**
032    * This method is used to determine if the cache is empty. This
033    * is done by checking if there are any elements in the cache.
034    * If anything has been cached this will return false.
035    * 
036    * @return this returns true if the cache is empty
037    */
038   boolean isEmpty();
039   
040   /**
041    * This method is used to insert a key value mapping in to the
042    * cache. The value can later be retrieved or removed from the
043    * cache if desired. If the value associated with the key is 
044    * null then nothing is stored within the cache.
045    * 
046    * @param key this is the key to cache the provided value to
047    * @param value this is the value that is to be cached
048    */
049   void cache(Object key, T value);
050 
051   /**
052    * This is used to exclusively take the value mapped to the 
053    * specified key from the cache. Invoking this is effectively
054    * removing the value from the cache.
055    * 
056    * @param key this is the key to acquire the cache value with
057    * 
058    * @return this returns the value mapped to the specified key 
059    */
060   T take(Object key);
061   
062   /**
063    * This method is used to get the value from the cache that is
064    * mapped to the specified key. If there is no value mapped to
065    * the specified key then this method will return a null.
066    * 
067    * @param key this is the key to acquire the cache value with
068    * 
069    * @return this returns the value mapped to the specified key 
070    */
071   T fetch(Object key);   
072   
073   /**
074    * This is used to determine whether the specified key exists
075    * with in the cache. Typically this can be done using the 
076    * fetch method, which will acquire the object. 
077    * 
078    * @param key this is the key to check within this segment
079    * 
080    * @return true if the specified key is within the cache
081    */
082   boolean contains(Object key);
083}