content: /*
   * Cache.java July 2006
   *
   * Copyright (C) 2006, Niall Gallagher <niallg@users.sf.net>
   *
   * Licensed 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 com.aliyun.odps.simpleframework.xml.util;
  
  /**
   * The <code>Cache</code> interface is used to represent a cache
   * that will store key value pairs. The cache exposes only several
   * methods to ensure that implementations can focus on performance
   * concerns rather than how to manage the cached values.
   * 
   * @author Niall Gallagher
   */
  public interface Cache<T> {
     
     /**
      * This method is used to determine if the cache is empty. This
      * is done by checking if there are any elements in the cache.
      * If anything has been cached this will return false.
      * 
      * @return this returns true if the cache is empty
      */
     boolean isEmpty();
     
     /**
      * This method is used to insert a key value mapping in to the
      * cache. The value can later be retrieved or removed from the
      * cache if desired. If the value associated with the key is 
      * null then nothing is stored within the cache.
      * 
      * @param key this is the key to cache the provided value to
      * @param value this is the value that is to be cached
      */
     void cache(Object key, T value);
   
     /**
      * This is used to exclusively take the value mapped to the 
      * specified key from the cache. Invoking this is effectively
      * removing the value from the cache.
      * 
      * @param key this is the key to acquire the cache value with
      * 
      * @return this returns the value mapped to the specified key 
      */
     T take(Object key);
     
     /**
      * This method is used to get the value from the cache that is
      * mapped to the specified key. If there is no value mapped to
      * the specified key then this method will return a null.
      * 
      * @param key this is the key to acquire the cache value with
      * 
      * @return this returns the value mapped to the specified key 
      */
     T fetch(Object key);   
     
     /**
      * This is used to determine whether the specified key exists
      * with in the cache. Typically this can be done using the 
      * fetch method, which will acquire the object. 
      * 
      * @param key this is the key to check within this segment
      * 
      * @return true if the specified key is within the cache
      */
     boolean contains(Object key);
  }