/*******************************************************************************
* Copyright (c) 1998, 2015 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.tools.workbench.uitools.app;
import org.eclipse.persistence.tools.workbench.utility.iterators.NullIterator;
/**
* A read-only collection value model for when you
* don't need to support a collection. In particular, this
* is useful for the leaf nodes of a tree that never have
* children.
*/
public final class NullCollectionValueModel
extends AbstractReadOnlyCollectionValueModel
{
private static final long serialVersionUID = 1L;
// singleton
private static NullCollectionValueModel INSTANCE;
/**
* Return the singleton.
*/
public static synchronized CollectionValueModel instance() {
if (INSTANCE == null) {
INSTANCE = new NullCollectionValueModel();
}
return INSTANCE;
}
/**
* Ensure non-instantiability.
*/
private NullCollectionValueModel() {
super();
}
// ********** CollectionValueModel implementation **********
/**
* @see CollectionValueModel#size()
*/
public int size() {
return 0;
}
/**
* @see ValueModel#getValue()
*/
public Object getValue() {
return NullIterator.instance();
}
// ********** Object overrides **********
/**
* @see Object#toString()
*/
public String toString() {
return "NullCollectionValueModel";
}
/**
* Serializable singleton support
*/
private Object readResolve() {
return instance();
}
}