org.eclipse.xtext.nodemodel.BidiIterator Maven / Gradle / Ivy

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/*******************************************************************************
 * Copyright (c) 2010 itemis AG (http://www.itemis.eu) and others.
 * 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
 *******************************************************************************/
package org.eclipse.xtext.nodemodel;

import java.util.Iterator;
import java.util.NoSuchElementException;

/**
 * A bidirectional iterator. It can be used in both directions and even alternating.
 * It is similar to a {@link java.util.ListIterator ListIterator} besides that it does not
 * support the index-based operations {@link java.util.ListIterator#previousIndex() previousIndex} and
 * {@link java.util.ListIterator#nextIndex() nextIndex} or the mutating operations 
 * {@link java.util.ListIterator#set(Object) set} and
 * {@link java.util.ListIterator#add(Object) add}.
 * @author Sebastian Zarnekow - Initial contribution and API
 */
public interface BidiIterator extends Iterator {

	/**
     * Returns true if this bidi iterator has more elements when
     * traversing in the reverse direction.  (In other words, returns
     * true if previous would return an element rather than
     * throwing an exception.)
     *
     * @return true if the bidi iterator has more elements when
     *	       traversing in the reverse direction.
     */
	boolean hasPrevious();
	
	/**
     * Returns the previous element.  This method may be called
     * repeatedly to iterate backwards, or intermixed with
     * calls to next to go back and forth.  (Note that alternating
     * calls to next and previous will return the same
     * element repeatedly.)
     *
     * @return the previous element.
     * 
     * @exception NoSuchElementException if the iteration has no previous
     *            element.
     */
	T previous();
	
}