/*
* JBoss, Home of Professional Open Source
* Copyright 2005, JBoss Inc., and individual contributors as indicated
* by the @authors tag. See the copyright.txt in the distribution for a
* full listing of individual contributors.
*
* This is free software; you can redistribute it and/or modify it
* under the terms of the GNU Lesser General Public License as
* published by the Free Software Foundation; either version 2.1 of
* the License, or (at your option) any later version.
*
* This software is distributed in the hope that it will be useful,
* but WITHOUT ANY WARRANTY; without even the implied warranty of
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
* Lesser General Public License for more details.
*
* You should have received a copy of the GNU Lesser General Public
* License along with this software; if not, write to the Free
* Software Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA
* 02110-1301 USA, or see the FSF site: http://www.fsf.org.
*/
package org.jboss.util;

/**
 * Interface that specifies a policy for caches. <p>
 * Implementation classes can implement a LRU policy, a random one, 
 * a MRU one, or any other suitable policy.
 * 
 * @author <a href="mailto:simone.bordet@compaq.com">Simone Bordet</a>
 * @version $Revision$
 */
public interface CachePolicy
{
   /**
    * Returns the object paired with the specified key if it's 
    * present in the cache, otherwise must return null. <br>
    * Implementations of this method must have complexity of order O(1).
    * Differently from {@link #peek} this method not only return whether
    * the object is present in the cache or not, but also 
    * applies the implemented policy that will "refresh" the cached 
    * object in the cache, because this cached object
    * was really requested.
    * 
    * @param key the key paired with the object
    * @see #peek
    */
   Object get(Object key);

   /**
    * Returns the object paired with the specified key if it's 
    * present in the cache, otherwise must return null. <br>
    * Implementations of this method must have complexity of order O(1).
    * This method should not apply the implemented caching policy to the 
    * object paired with the given key, so that a client can 
    * query if an object is cached without "refresh" its cache status. Real 
    * requests for the object must be done using {@link #get}.
    * 
    * @param key the key paired with the object
    * @see #get
    */	
   Object peek(Object key);
   
   /**
    * Inserts the specified object into the cache following the 
    * implemented policy. <br>
    * Implementations of this method must have complexity of order O(1).
    * 
    * @param key the key paired with the object
    * @param object the object to cache
    * @see #remove
    */
   void insert(Object key, Object object);
   
   /**
    * Remove the cached object paired with the specified key. <br>
    * Implementations of this method must have complexity of order O(1).
    * 
    * @param key the key paired with the object
    * @see #insert
    */
   void remove(Object key);
   
   /**
    * Flushes the cached objects from the cache.
    */
   void flush();

   /**
    * Get the size of the cache.
    */
   int size();



   /**
    * create the service, do expensive operations etc 
    */
   void create() throws Exception;
   
   /**
    * start the service, create is already called
    */
   void start() throws Exception;
   
   /**
    * stop the service
    */
   void stop();
   
   /**
    * destroy the service, tear down 
    */
   void destroy();
}
