cachepolicy.java

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/**
 * JDBM LICENSE v1.00
 *
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 * that the following conditions are met:
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 * 1. Redistributions of source code must retain copyright
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 *    copy of this document.
 *
 * 2. Redistributions in binary form must reproduce the
 *    above copyright notice, this list of conditions and the
 *    following disclaimer in the documentation and/or other
 *    materials provided with the distribution.
 *
 * 3. The name "JDBM" must not be used to endorse or promote
 *    products derived from this Software without prior written
 *    permission of Cees de Groot.  For written permission,
 *    please contact [e-mail].
 *
 * 4. Products derived from this Software may not be called "JDBM"
 *    nor may "JDBM" appear in their names without prior written
 *    permission of Cees de Groot.
 *
 * 5. Due credit should be given to the JDBM Project
 *    (http://jdbm.sourceforge.net/).
 *
 * THIS SOFTWARE IS PROVIDED BY THE JDBM PROJECT AND CONTRIBUTORS
 * ``AS IS'' AND ANY EXPRESSED OR IMPLIED WARRANTIES, INCLUDING, BUT
 * NOT LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND
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 * CEES DE GROOT OR ANY CONTRIBUTORS BE LIABLE FOR ANY DIRECT,
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 *
 * Copyright 2000 (C) Cees de Groot. All Rights Reserved.
 * Contributions are Copyright (C) 2000 by their associated contributors.
 *
 * $Id: CachePolicy.java,v 1.5 2003/11/01 13:25:02 dranatunga Exp $
 */

package jdbm.helper;

import java.util.Enumeration;

/**
 *  CachePolicity is an abstraction for different cache policies.
 *  (ie. MRU, time-based, soft-refs, ...)
 *
 * @author <a href="mailto:[e-mail]">Alex Boisvert</a>
 * @author <a href="mailto:[e-mail]">Dilum Ranatunga</a>
 * @version $Id: CachePolicy.java,v 1.5 2003/11/01 13:25:02 dranatunga Exp $
 */
public interface CachePolicy
{

    /**
     * Place an object in the cache. If the cache does not currently contain
     * an object for the key specified, this mapping is added. If an object
     * currently exists under the specified key, the current object is
     * replaced with the new object.
     * <p>
     * If the changes to the cache cause the eviction of any objects
     * <strong>stored under other key(s)</strong>, events corresponding to
     * the evictions are fired for each object. If an event listener is
     * unable to handle the eviction, and throws a cache eviction exception,
     * that exception is propagated to the caller. If such an exception is
     * thrown, the cache itself should be left as it was before the
     * <code>put()</code> operation was invoked: the the object whose
     * eviction failed is still in the cache, and the new insertion or
     * modification is reverted.
     *
     * @param key key for the cached object
     * @param value the cached object
     * @throws CacheEvictionException propagated if, while evicting objects
     *     to make room for new object, an eviction listener encountered
     *     this problem.
     */
    public void put( Object key, Object value )
        throws CacheEvictionException;


    /**
     * Obtain the object stored under the key specified.
     *
     * @param key key the object was cached under
     * @return the object if it is still in the cache, null otherwise.
     */
    public Object get( Object key );


    /**
     * Remove the object stored under the key specified. Note that since
     * eviction notices are only fired when objects under <strong>different
     * keys</strong> are evicted, no event is fired for any object stored
     * under this key (see {@link #put(Object, Object) put( )}).
     *
     * @param key key the object was stored in the cache under.
     */
    public void remove( Object key );


    /**
     * Remove all objects from the cache. Consistent with
     * {@link #remove(Object) remove( )}, no eviction notices are fired.
     */
    public void removeAll();


    /**
     * Enumerate through the objects currently in the cache.
     */
    public Enumeration elements();


    /**
     * Add a listener to this cache policy.
     * <p>
     * If this cache policy already contains a listener that is equal to
     * the one being added, this call has no effect.
     *
     * @param listener the (non-null) listener to add to this policy
     * @throws IllegalArgumentException if listener is null.
     */
    public void addListener( CachePolicyListener listener )
            throws IllegalArgumentException;

    
    /**
     * Remove a listener from this cache policy. The listener is found
     * using object equality, not identity.
     *
     * @param listener the listener to remove from this policy
     */
    public void removeListener( CachePolicyListener listener );

}