001 /**
002 * JDBM LICENSE v1.00
003 *
004 * Redistribution and use of this software and associated documentation
005 * ("Software"), with or without modification, are permitted provided
006 * that the following conditions are met:
007 *
008 * 1. Redistributions of source code must retain copyright
009 * statements and notices. Redistributions must also contain a
010 * copy of this document.
011 *
012 * 2. Redistributions in binary form must reproduce the
013 * above copyright notice, this list of conditions and the
014 * following disclaimer in the documentation and/or other
015 * materials provided with the distribution.
016 *
017 * 3. The name "JDBM" must not be used to endorse or promote
018 * products derived from this Software without prior written
019 * permission of Cees de Groot. For written permission,
020 * please contact cg@cdegroot.com.
021 *
022 * 4. Products derived from this Software may not be called "JDBM"
023 * nor may "JDBM" appear in their names without prior written
024 * permission of Cees de Groot.
025 *
026 * 5. Due credit should be given to the JDBM Project
027 * (http://jdbm.sourceforge.net/).
028 *
029 * THIS SOFTWARE IS PROVIDED BY THE JDBM PROJECT AND CONTRIBUTORS
030 * ``AS IS'' AND ANY EXPRESSED OR IMPLIED WARRANTIES, INCLUDING, BUT
031 * NOT LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND
032 * FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL
033 * CEES DE GROOT OR ANY CONTRIBUTORS BE LIABLE FOR ANY DIRECT,
034 * INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES
035 * (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR
036 * SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
037 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT,
038 * STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
039 * ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED
040 * OF THE POSSIBILITY OF SUCH DAMAGE.
041 *
042 * Copyright 2000 (C) Cees de Groot. All Rights Reserved.
043 * Contributions are Copyright (C) 2000 by their associated contributors.
044 *
045 * $Id: CachePolicy.java,v 1.5 2003/11/01 13:25:02 dranatunga Exp $
046 */
047 package jdbm.helper;
048
049
050 import java.util.Enumeration;
051
052
053 /**
054 * CachePolicity is an abstraction for different cache policies.
055 * (ie. MRU, time-based, soft-refs, ...)
056 *
057 * @author <a href="mailto:boisvert@intalio.com">Alex Boisvert</a>
058 * @author <a href="mailto:dranatunga@users.sourceforge.net">Dilum Ranatunga</a>
059 * @version $Id: CachePolicy.java,v 1.5 2003/11/01 13:25:02 dranatunga Exp $
060 */
061 public interface CachePolicy<K,V>
062 {
063 /**
064 * Place an object in the cache. If the cache does not currently contain
065 * an object for the key specified, this mapping is added. If an object
066 * currently exists under the specified key, the current object is
067 * replaced with the new object.
068 * <p>
069 * If the changes to the cache cause the eviction of any objects
070 * <strong>stored under other key(s)</strong>, events corresponding to
071 * the evictions are fired for each object. If an event listener is
072 * unable to handle the eviction, and throws a cache eviction exception,
073 * that exception is propagated to the caller. If such an exception is
074 * thrown, the cache itself should be left as it was before the
075 * <code>put()</code> operation was invoked: the the object whose
076 * eviction failed is still in the cache, and the new insertion or
077 * modification is reverted.
078 *
079 * @param key key for the cached object
080 * @param value the cached object
081 * @throws CacheEvictionException propagated if, while evicting objects
082 * to make room for new object, an eviction listener encountered
083 * this problem.
084 */
085 public void put( K key, V value ) throws CacheEvictionException;
086
087
088 /**
089 * Obtain the object stored under the key specified.
090 *
091 * @param key key the object was cached under
092 * @return the object if it is still in the cache, null otherwise.
093 */
094 public V get( K key );
095
096
097 /**
098 * Remove the object stored under the key specified. Note that since
099 * eviction notices are only fired when objects under <strong>different
100 * keys</strong> are evicted, no event is fired for any object stored
101 * under this key (see {@link #put(Object, Object) put( )}).
102 *
103 * @param key key the object was stored in the cache under.
104 */
105 public void remove( K key );
106
107
108 /**
109 * Remove all objects from the cache. Consistent with
110 * {@link #remove(Object) remove( )}, no eviction notices are fired.
111 */
112 public void removeAll();
113
114
115 /**
116 * Enumerate through the objects currently in the cache.
117 */
118 public Enumeration<V> elements();
119
120
121 /**
122 * Add a listener to this cache policy.
123 * <p>
124 * If this cache policy already contains a listener that is equal to
125 * the one being added, this call has no effect.
126 *
127 * @param listener the (non-null) listener to add to this policy
128 * @throws IllegalArgumentException if listener is null.
129 */
130 public void addListener( CachePolicyListener<V> listener ) throws IllegalArgumentException;
131
132
133 /**
134 * Remove a listener from this cache policy. The listener is found
135 * using object equality, not identity.
136 *
137 * @param listener the listener to remove from this policy
138 */
139 public void removeListener( CachePolicyListener<V> listener );
140 }