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Java > Open Source Codes > org > nemesis > forum > util > cache > CacheObject


1 /*
2  * NEMESIS-FORUM.
3  * Copyright (C) 2002 David Laurent(lithium2@free.fr). All rights reserved.
4  *
5  * Copyright (c) 2000 The Apache Software Foundation. All rights reserved.
6  *
7  * Copyright (C) 2001 Yasna.com. All rights reserved.
8  *
9  * Copyright (C) 2000 CoolServlets.com. All rights reserved.
10  *
11  * NEMESIS-FORUM. is free software; you can redistribute it and/or
12  * modify it under the terms of the Apache Software License, Version 1.1,
13  * or (at your option) any later version.
14  *
15  * NEMESIS-FORUM core framework, NEMESIS-FORUM backoffice, NEMESIS-FORUM frontoffice
16  * application are parts of NEMESIS-FORUM and are distributed under
17  * same terms of licence.
18  *
19  *
20  * NEMESIS-FORUM includes software developed by the Apache Software Foundation (http://www.apache.org/)
21  * and software developed by CoolServlets.com (http://www.coolservlets.com).
22  * and software developed by Yasna.com (http://www.yasna.com).
23  *
24  */
25
26 package org.nemesis.forum.util.cache;
27
28 import org.nemesis.forum.util.LinkedListNode;
29
30 /**
31  * Wrapper for all objects put into cache. It's primary purpose is to maintain
32  * references to the linked lists that maintain the creation time of the object
33  * and the ordering of the most used objects.
34  *
35  * This class is optimized for speed rather than strictly correct encapsulation.
36  */
37 public final class CacheObject {
38
39    /**
40     * Underlying object wrapped by the CacheObject.
41     */
42     public Cacheable object;
43
44     /**
45      * The size of the Cacheable object. The size of the Cacheable
46      * object is only computed once when it is added to the cache. This makes
47      * the assumption that once objects are added to cache, they are mostly
48      * read-only and that their size does not change significantly over time.
49      */
50     public int size;
51
52     /**
53      * A reference to the node in the cache order list. We keep the reference
54      * here to avoid linear scans of the list. Every time the object is
55      * accessed, the node is removed from its current spot in the list and
56      * moved to the front.
57      */
58     public LinkedListNode lastAccessedListNode;
59
60     /**
61      * A reference to the node in the age order list. We keep the reference
62      * here to avoid linear scans of the list. The reference is used if the
63      * object has to be deleted from the list.
64      */
65     public LinkedListNode ageListNode;
66
67     /**
68      * Creates a new cache object wrapper. The size of the Cacheable object
69      * must be passed in in order to prevent another possibly expensive
70      * lookup by querying the object itself for its size.<p>
71      *
72      * @param object the underlying Cacheable object to wrap.
73      * @param size the size of the Cachable object in bytes.
74      */
75     public CacheObject(Cacheable object, int size) {
76         this.object = object;
77         this.size = size;
78     }
79 }
80
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