/*
 * Copyright (C) 2005-2007 Alfresco Software Limited.
 *
 * This program is free software; you can redistribute it and/or
 * modify it under the terms of the GNU General Public License
 * as published by the Free Software Foundation; either version 2
 * of the License, or (at your option) any later version.

 * This program 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 General Public License for more details.

 * You should have received a copy of the GNU General Public License
 * along with this program; if not, write to the Free Software
 * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301, USA.

 * As a special exception to the terms and conditions of version 2.0 of 
 * the GPL, you may redistribute this Program in connection with Free/Libre 
 * and Open Source Software ("FLOSS") applications as described in Alfresco's 
 * FLOSS exception.  You should have recieved a copy of the text describing 
 * the FLOSS exception, and it is also available here: 
 * http://www.alfresco.com/legal/licensing"
 */
package org.alfresco.repo.cache;

import java.io.Serializable;
import java.util.Collection;

/**
 * Basic caching interface.
 * <p>
 * All implementations <b>must</b> be thread-safe.  Additionally, the use of the
 * <tt>Serializable</tt> for both keys and values ensures that the underlying
 * cache implementations can support both clustered caches as well as persistent
 * caches.
 * <p>
 * All implementations must support <tt>null</tt> values.  It therefore follows
 * that
 * <pre>
 *    (simpleCache.contains(key) == true) does not imply (simpleCache.get(key) != null)
 * </pre>
 * but
 * <pre>
 *    (simpleCache.contains(key) == false) implies (simpleCache.get(key) == null)
 * <pre>
 * 
 * @author Derek Hulley
 */
public interface SimpleCache<K extends Serializable, V extends Object>
{
    /**
     * @param key       the cache key to check up on
     * @return          Returns <tt>true</tt> if there is a cache entry,
     *                  regardless of whether the value itself is <tt>null</tt>
     */
    public boolean contains(K key);
    
    public Collection<K> getKeys();
    
    /**
     * @param key
     * @return          Returns the value associated with the key.  It will be <tt>null</tt>
     *                  if the value is <tt>null</tt> or if the cache doesn't have an entry.
     */
    public V get(K key);
    
    /**
     * @param key       the key against which to store the value
     * @param value     the value to store.  <tt>null</tt> is allowed.
     */
    public void put(K key, V value);
    
    /**
     * Removes the cache entry whether or not the value stored against it is <tt>null</tt>.
     * 
     * @param key       the key value to remove
     */
    public void remove(K key);
    
    public void clear();
}