/******************************************************************************* | |
* Copyright (c) 1998, 2013 Oracle and/or its affiliates. All rights reserved. | |
* This program and the accompanying materials are made available under the | |
* terms of the Eclipse Public License v1.0 and Eclipse Distribution License v. 1.0 | |
* which accompanies this distribution. | |
* The Eclipse Public License is available at http://www.eclipse.org/legal/epl-v10.html | |
* and the Eclipse Distribution License is available at | |
* http://www.eclipse.org/org/documents/edl-v10.php. | |
* | |
* Contributors: | |
* Oracle - initial API and implementation from Oracle TopLink | |
******************************************************************************/ | |
package org.eclipse.persistence.internal.helper; | |
/** | |
* <b>Purpose</b>:Indicates an object that should not be returned from | |
* query execution. | |
* <p> | |
* When conforming if checkEarly return finds a matching object by exact primary | |
* key, but that object is deleted, want to return null from query execution. | |
* <p> | |
* However if null is returned from checkEarly return that will indicate that | |
* no object was found and to go to the database. Hence returning null is not | |
* enough, something else needed to be returned, indicating not only that | |
* checkEarlyReturn had failed but query execution should not proceed. | |
* <p> | |
* Can be used in other instances where returning null is ambiguous. | |
* <p> | |
* Implements singleton pattern | |
* @author Stephen McRitchie | |
*/ | |
public class InvalidObject { | |
public static final InvalidObject instance = new InvalidObject(); | |
private InvalidObject() { | |
} | |
/** | |
* @return singleton invalid object. | |
*/ | |
public static InvalidObject instance() { | |
return instance; | |
} | |
} |