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Wed Mar 24 16:00:00 GMT 2004
OpenListIteration
package examples.iterator.aspectj; /* -*- Mode: Java; tab-width: 4; indent-tabs-mode: nil; c-basic-offset: 4 -*- * * This file is part of the design patterns project at UBC * * The contents of this file are subject to the Mozilla Public License * Version 1.1 (the "License"); you may not use this file except in * compliance with the License. You may obtain a copy of the License at * either http://www.mozilla.org/MPL/ or http://aspectj.org/MPL/. * * Software distributed under the License is distributed on an "AS IS" basis, * WITHOUT WARRANTY OF ANY KIND, either express or implied. See the License * for the specific language governing rights and limitations under the * License. * * The Original Code is ca.ubc.cs.spl.patterns. * * Contributor(s): */ import java.util.NoSuchElementException; import java.util.Iterator; /** * Implements a concrete instance of the Iterator design pattern. This * concrete aspect attaches a factory method to the <i>Aggregate</i> class * and provides an implementation for the Iterator via an inner class. * * @author Jan Hannemann * @author Gregor Kiczales * @version 1.0, 07/13/02 * * @see SimpleList * @see OpenList */ public aspect OpenListIteration { /** * Attaches the factory method to create the reverse iterator to the * OpenList class using the open classes mechanism. */ Iterator OpenList.createReverseIterator() { return new ReverseIterator(this); } /** * Another possibility of where to place the factory method. If we * have the factory method on the aspect, multiple instances of the * same pattern will not be confused an can use the same aggregate * (multiple factory methods won't conflict that way, even if they * have the same signature). This is the preferrable implementation. */ Iterator createIteratorFor(OpenList list) { return new ReverseIterator(list); } /** * Provides the implementation of the reverse iterator. Instead * of defining an inner class, one could also instantiate * <code>java.util.Iterator</code> as an anonymous class and overwrite * the appropriate methods. */ private static class ReverseIterator implements Iterator { /** * the positition of the current element */ protected int current; /** * the list this iterator operates on */ protected SimpleList list; /** * Returns true if the iteration has more elements. * * @returns true if the iteration has more elements */ public boolean hasNext() { return (current > 0); } /** * This opional method is not implemented for this iterator. */ public void remove() { throw new UnsupportedOperationException("remove() not supported"); } /** * Returns the next element in the iteration. * * @returns the next element in the iteration. */ public Object next() { if (!hasNext()) { throw new ArrayIndexOutOfBoundsException("Iterator out of Bounds"); } else { return list.get(--current); } } /** * Creates a new ReverseIterator from the given list. * * @param list the list to generate an iterator from */ public ReverseIterator(SimpleList list) { super(); this.list = list; current = list.count(); } } }
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