NullListValueModel.java

/*******************************************************************************
 * 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.NullListIterator;

/**
 * A read-only list value model for when you don't
 * need to support a list.
 */
public final class NullListValueModel
    extends AbstractReadOnlyListValueModel
{

    private static final long serialVersionUID = 1L;

    // singleton
    private static NullListValueModel INSTANCE;

    /**
     * Return the singleton.
     */
    public static synchronized ListValueModel instance() {
        if (INSTANCE == null) {
            INSTANCE = new NullListValueModel();
        }
        return INSTANCE;
    }

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


    // ********** ListValueModel implementation **********

    /**
     * @see ListValueModel#size()
     */
    public int size() {
        return 0;
    }

    /**
     * @see ValueModel#getValue()
     */
    public Object getValue() {
        return NullListIterator.instance();
    }


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

    /**
     * @see Object#toString()
     */
    public String toString() {
        return "NullListValueModel";
    }

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

}