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/*******************************************************************************
* 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;
/**
* Purpose:Indicates an object that should not be returned from
* query execution.
*
* 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.
*
* 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.
*
* Can be used in other instances where returning null is ambiguous.
*
* 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;
}
}