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Wed Mar 24 16:00:00 GMT 2004
QueueStateAspect
package examples.state.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.pattern. * * Contributor(s): */ /** * Implements the state transitions for this state design pattern example. * State transitions are realizied as <code>after</code> advice. The * joinpoints are the calls from the context to its state object.<p> * * Exisiting states are reused without a employing a flyweight mechanism or * (inflexibly) modularizing the transitions in the context. * * @author Jan Hannemann * @author Gregor Kiczales * @version 1.0, 06/13/02 * */ public aspect QueueStateAspect { /** * the queue's "empty" state */ protected QueueEmpty empty = new QueueEmpty(); /** * the queue's "normal" state */ protected QueueNormal normal = new QueueNormal(); /** * the queue's "full" state */ protected QueueFull full = new QueueFull(); /** * Sets the initial state of the queue to empty. * * @param queue the queue context that is initialized. */ after(Queue queue): initialization(new()) && target(queue) { queue.setState(empty); } /** * Updates the queue context's state after each call from it to the * <code>insert(Object)</code> method if its current state. * * @param queue the queue context that makes the call. * @param qs the current QueueState that receives the call * @param arg the object to be inserted. */ after(Queue queue, QueueState qs, Object arg): call(boolean QueueState+.insert(Object)) && target(qs) && args(arg) && this(queue) { if (qs == empty) { normal.insert(arg); queue.setState(normal); } else if (qs == normal) { if (normal.first == normal.last) { full.items = normal.items; full.first = normal.first; queue.setState(full); } } } /** * Updates the queue context's state after each call from it to the * <code>removeFirst()</code> method if its current state. * * @param queue the queue context that makes the call. * @param qs the current QueueState that receives the call */ after(Queue queue, QueueState qs): call(boolean QueueState+.removeFirst()) && target(qs) && this(queue) { if (qs == full) { normal.items = full.items; normal.last = full.first; normal.first = (full.first +1) % normal.items.length; queue.setState(normal); } else if (qs == normal) { if (normal.first == normal.last) { queue.setState(empty); } } } }
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