SingleElementListIterator.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.ListIterator;
import java.util.NoSuchElementException;

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


/**
 * A <code>SingleElementListIterator</code> holds a single element
 * and returns it with the first call to <code>next()</code>, at
 * which point it will return <code>false</code> to any subsequent
 * call to <code>hasNext()</code>. Likewise, it will return <code>false</code>
 * to a call to <code>hasPrevious()</code> until a call to <code>next()</code>,
 * at which point a call to <code>previous()</code> will return the
 * single element.
 * <p>
 * A <code>SingleElementIterator</code> is equivalent to the
 * <code>Iterator</code> returned by:
 *     <code>java.util.Collections.singletonList(element).listIterator()</code>
 */
public class SingleElementListIterator implements ListIterator {
    private Object element;
    private Object next;

    private static final Object END = new Object();


    /**
     * Construct a list iterator that returns only the specified element.
     */
    public SingleElementListIterator(Object element) {
        super();
        this.element = element;
        this.next = element;
    }

    /**
     * @see java.util.ListIterator#hasNext()
     */
    public boolean hasNext() {
        return this.next == this.element;
    }

    /**
     * @see java.util.ListIterator#next()
     */
    public Object next() {
        if (this.next == END) {
            throw new NoSuchElementException();
        }
        this.next = END;
        return this.element;
    }

    /**
     * @see java.util.ListIterator#nextIndex()
     */
    public int nextIndex() {
        return (this.next == this.element) ? 0 : 1;
    }

    /**
     * @see java.util.ListIterator#hasPrevious()
     */
    public boolean hasPrevious() {
        return this.next == END;
    }

    /**
     * @see java.util.ListIterator#previous()
     */
    public Object previous() {
        if (this.next == this.element) {
            throw new NoSuchElementException();
        }
        this.next = this.element;
        return this.element;
    }

    /**
     * @see java.util.ListIterator#nextIndex()
     */
    public int previousIndex() {
        return (this.next == END) ? 0 : -1;
    }

    /**
     * @see java.util.ListIterator#add(Object)
     */
    public void add(Object o) {
        throw new UnsupportedOperationException();
    }

    /**
     * @see java.util.ListIterator#set(Object)
     */
    public void set(Object o) {
        throw new UnsupportedOperationException();
    }

    /**
     * @see java.util.ListIterator#remove()
     */
    public void remove() {
        throw new UnsupportedOperationException();
    }

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

}