jpa/plugins/org.eclipse.jpt.utility/src/org/eclipse/jpt/utility/internal/model/value/NullCollectionValueModel.java

/*******************************************************************************
 * Copyright (c) 2007 Oracle. All rights reserved.
 * This program and the accompanying materials are made available under the
 * terms of the Eclipse Public License v1.0, which accompanies this distribution
 * and is available at http://www.eclipse.org/legal/epl-v10.html.
 * 
 * Contributors:
 *     Oracle - initial API and implementation
 ******************************************************************************/
package org.eclipse.jpt.utility.internal.model.value;

import java.util.Iterator;

import org.eclipse.jpt.utility.internal.iterators.EmptyIterator;


/**
 * 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 final NullCollectionValueModel INSTANCE = new NullCollectionValueModel();

	/**
	 * Return the singleton.
	 */
	public static synchronized CollectionValueModel instance() {
		return INSTANCE;
	}

	/**
	 * Ensure non-instantiability.
	 */
	private NullCollectionValueModel() {
		super();
	}
	

	// ********** CollectionValueModel implementation **********

	@Override
	public int size() {
		return 0;
	}

	public Iterator iterator() {
		return EmptyIterator.instance();
	}


	// ********** Object overrides **********

    @Override
	public String toString() {
		return "NullCollectionValueModel";
	}

	/**
	 * Serializable singleton support
	 */
	private Object readResolve() {
		return instance();
	}

}