NullEnumeration.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.utility.iterators;

import java.util.Enumeration;
import java.util.NoSuchElementException;

import org.eclipse.persistence.tools.workbench.utility.ClassTools;


/**
 * A <code>NullEnumeration</code> is just that.
 */
public final class NullEnumeration implements Enumeration {

    // singleton
    private static NullEnumeration INSTANCE;

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

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

    /**
     * @see java.util.Enumeration#hasMoreElements()
     */
    public boolean hasMoreElements() {
        return false;
    }

    /**
     * @see java.util.Enumeration#nextElement()
     */
    public Object nextElement() {
        throw new NoSuchElementException();
    }

    /**
     * @see Object#toString()
     */
    public String toString() {
        return ClassTools.shortClassNameForObject(this);
    }

}