SoftCacheWeakIdentityMap


1   /*
2    * The contents of this file are subject to the terms 
3    * of the Common Development and Distribution License 
4    * (the "License").  You may not use this file except 
5    * in compliance with the License.
6    * 
7    * You can obtain a copy of the license at 
8    * glassfish/bootstrap/legal/CDDLv1.0.txt or 
9    * https://glassfish.dev.java.net/public/CDDLv1.0.html. 
10   * See the License for the specific language governing 
11   * permissions and limitations under the License.
12   * 
13   * When distributing Covered Code, include this CDDL 
14   * HEADER in each file and include the License file at 
15   * glassfish/bootstrap/legal/CDDLv1.0.txt.  If applicable, 
16   * add the following below this CDDL HEADER, with the 
17   * fields enclosed by brackets "[]" replaced with your 
18   * own identifying information: Portions Copyright [yyyy] 
19   * [name of copyright owner]
20   */
21  // Copyright (c) 1998, 2005, Oracle. All rights reserved.  
22  package oracle.toplink.essentials.internal.identitymaps;
23  
24  import java.lang.ref.*;
25  
26  /**
27   * <p><b>Purpose</b>: A weak cache is identical to the weak identity map, however the weak
28   * can be a performance problem for some types of apps because it can cause too much garbage collection
29   * of objects read causing them to be re-read and re-built (this defeats the purpose of the cache).
30   * The weak cache solves this through also holding a fixed number of objects is memory to improve caching.
31   * <p><b>Responsibilities</b>:<ul>
32   * <li> Guarantees identity
33   * <li> Allows garbage collection
34   * <li> Increases performance through maintaining a fixed size cache of MRU objects when memory is available
35   * <li> The default size of the reference cache is half the max size
36   * </ul>
37   * @since TOPLink/Java 1.2
38   */
39  public class SoftCacheWeakIdentityMap extends HardCacheWeakIdentityMap {
40      public SoftCacheWeakIdentityMap(int size) {
41          super(size);
42      }
43  
44      /**
45       * Creates a Soft reference if Required
46       * @param object is the domain object to cache.
47       */
48      public Object   buildReference(Object   object) {
49          return new SoftReference(object);
50      }
51  
52      /**
53       * Checks if the object is null, or reference's object is null.
54       * @param the object for hard or the reference for soft.
55       */
56      public boolean hasReference(Object   reference) {
57          return (reference != null) && (((SoftReference)reference).get() != null);
58      }
59  }
60
A to Z: JavaDoc & Examples Daily Java News & Articles Open Source Projects Open Source Codes Free Computer Books Remove Frame
Popular Tags