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1   /**
2    * JDBM LICENSE v1.00
3    *
4    * Redistribution and use of this software and associated documentation
5    * ("Software"), with or without modification, are permitted provided
6    * that the following conditions are met:
7    *
8    * 1. Redistributions of source code must retain copyright
9    *    statements and notices.  Redistributions must also contain a
10   *    copy of this document.
11   *
12   * 2. Redistributions in binary form must reproduce the
13   *    above copyright notice, this list of conditions and the
14   *    following disclaimer in the documentation and/or other
15   *    materials provided with the distribution.
16   *
17   * 3. The name "JDBM" must not be used to endorse or promote
18   *    products derived from this Software without prior written
19   *    permission of Cees de Groot.  For written permission,
20   *    please contact cg@cdegroot.com.
21   *
22   * 4. Products derived from this Software may not be called "JDBM"
23   *    nor may "JDBM" appear in their names without prior written
24   *    permission of Cees de Groot.
25   *
26   * 5. Due credit should be given to the JDBM Project
27   *    (http://jdbm.sourceforge.net/).
28   *
29   * THIS SOFTWARE IS PROVIDED BY THE JDBM PROJECT AND CONTRIBUTORS
30   * ``AS IS'' AND ANY EXPRESSED OR IMPLIED WARRANTIES, INCLUDING, BUT
31   * NOT LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND
32   * FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED.  IN NO EVENT SHALL
33   * CEES DE GROOT OR ANY CONTRIBUTORS BE LIABLE FOR ANY DIRECT,
34   * INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES
35   * (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR
36   * SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
37   * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT,
38   * STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
39   * ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED
40   * OF THE POSSIBILITY OF SUCH DAMAGE.
41   *
42   * Copyright 2000 (C) Cees de Groot. All Rights Reserved.
43   * Contributions are Copyright (C) 2000 by their associated contributors.
44   *
45   * $Id: CachePolicy.java,v 1.5 2003/11/01 13:25:02 dranatunga Exp $
46   */
47  
48  package jdbm.helper;
49  
50  import java.util.Enumeration;
51  
52  /**
53   *  CachePolicity is an abstraction for different cache policies.
54   *  (ie. MRU, time-based, soft-refs, ...)
55   *
56   * @author <a href="mailto:boisvert@intalio.com">Alex Boisvert</a>
57   * @author <a href="mailto:dranatunga@users.sourceforge.net">Dilum Ranatunga</a>
58   * @version $Id: CachePolicy.java,v 1.5 2003/11/01 13:25:02 dranatunga Exp $
59   */
60  public interface CachePolicy
61  {
62  
63      /**
64       * Place an object in the cache. If the cache does not currently contain
65       * an object for the key specified, this mapping is added. If an object
66       * currently exists under the specified key, the current object is
67       * replaced with the new object.
68       * <p>
69       * If the changes to the cache cause the eviction of any objects
70       * <strong>stored under other key(s)</strong>, events corresponding to
71       * the evictions are fired for each object. If an event listener is
72       * unable to handle the eviction, and throws a cache eviction exception,
73       * that exception is propagated to the caller. If such an exception is
74       * thrown, the cache itself should be left as it was before the
75       * <code>put()</code> operation was invoked: the the object whose
76       * eviction failed is still in the cache, and the new insertion or
77       * modification is reverted.
78       *
79       * @param key key for the cached object
80       * @param value the cached object
81       * @throws CacheEvictionException propagated if, while evicting objects
82       *     to make room for new object, an eviction listener encountered
83       *     this problem.
84       */
85      public void put( Object key, Object value )
86          throws CacheEvictionException;
87  
88  
89      /**
90       * Obtain the object stored under the key specified.
91       *
92       * @param key key the object was cached under
93       * @return the object if it is still in the cache, null otherwise.
94       */
95      public Object get( Object key );
96  
97  
98      /**
99       * Remove the object stored under the key specified. Note that since
100      * eviction notices are only fired when objects under <strong>different
101      * keys</strong> are evicted, no event is fired for any object stored
102      * under this key (see {@link #put(Object, Object) put( )}).
103      *
104      * @param key key the object was stored in the cache under.
105      */
106     public void remove( Object key );
107 
108 
109     /**
110      * Remove all objects from the cache. Consistent with
111      * {@link #remove(Object) remove( )}, no eviction notices are fired.
112      */
113     public void removeAll();
114 
115 
116     /**
117      * Enumerate through the objects currently in the cache.
118      */
119     public Enumeration elements();
120 
121 
122     /**
123      * Add a listener to this cache policy.
124      * <p>
125      * If this cache policy already contains a listener that is equal to
126      * the one being added, this call has no effect.
127      *
128      * @param listener the (non-null) listener to add to this policy
129      * @throws IllegalArgumentException if listener is null.
130      */
131     public void addListener( CachePolicyListener listener )
132             throws IllegalArgumentException;
133 
134     
135     /**
136      * Remove a listener from this cache policy. The listener is found
137      * using object equality, not identity.
138      *
139      * @param listener the listener to remove from this policy
140      */
141     public void removeListener( CachePolicyListener listener );
142 
143 }