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Java > Open Source Codes > oracle > toplink > essentials > internal > helper > InvalidObject


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
23 /* Copyright (c) 2004, 2005, Oracle. All rights reserved. */
24 /*
25    DESCRIPTION
26     <short description of component this file declares/defines>
27
28    PRIVATE CLASSES
29     <list of private classes defined - with one-line descriptions>
30
31    NOTES
32     <other useful comments, qualifications, etc.>
33
34    MODIFIED (MM/DD/YY)
35     pkrogh 10/07/05 -
36     pkrogh 09/29/05 -
37     gyorke 08/09/05 - gyorke_10-essentials-directory-creation_050808
38     dmahar 08/04/05 -
39     pkrogh 08/28/04 - codeformat
40     smcritch 05/14/04 - smcritch_refactor_session_read031604
41     smcritch 04/26/04 - Creation
42  */
43 package oracle.toplink.essentials.internal.helper;
44
45
46 /**
47  * <b>Purpose</b>:Indicates an object that should not be returned from
48  * query execution.
49  * <p>
50  * When conforming if checkEarly return finds a matching object by exact primary
51  * key, but that object is deleted, want to return null from query execution.
52  * <p>
53  * However if null is returned from checkEarly return that will indicate that
54  * no object was found and to go to the database. Hence returning null is not
55  * enough, something else needed to be returned, indicating not only that
56  * checkEarlyReturn had failed but query execution should not proceed.
57  * <p>
58  * Can be used in other instances where returning null is ambiguous.
59  * <p>
60  * Implements singleton pattern
61  * @author Stephen McRitchie
62  * @since release specific (what release of product did this appear in)
63  */
64 public class InvalidObject {
65     public static final InvalidObject instance = new InvalidObject();
66
67     private InvalidObject() {
68     }
69
70     /**
71      * @return singleton invalid object.
72      */
73     public static InvalidObject instance() {
74         return instance;
75     }
76 }
77
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