carfield.com.hk

Main.java

2004-03-24T16:00:00Z

package examples.state.java;

/* -*- 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 driver for the State design pattern example. 
 *
 * Intent: Allow an object to alter its behavior when its internal state
 * changes. The object will appear to change its class
 *
 * Participatng objects are <code>Queue</code> as Context, and 
 * <code>QueueNormal</code>, <code>QueueEmpty</code>, and <code>QueueFull
 * </code> as ConcreteStates. The State interface is defined in
 * <code>QueueState</code>. This version implements an update-on-demand
 * logic (see GoF, implementation 1, page 308). The logic requires passing
 * the context on calls to methods defined in the state interface, and an
 * interface for context objects. The interface is defined in 
 * <code>QueueContext</code>.
 * 
 *
 * This example of the State design pattern models a Queue ADT with
 * a limited capacity that has three different states: 
 * <UL>
 * <LI>Empty:	The queue is empty 
 * <LI>Normal: The queue is neither empty nor full
 * <LI>Full:	The queue is full (# of elements = capacity)
 * </UL>
 * The queue will store Objects to preserve generality. The following
 * operations are defined on Queue:
 * <UL>
 * <LI><code>insert(Object)</code> Inserts a new Object into the queue
 * <LI><code>getFirst():Object</code> Returns the first element in the queue
 * <LI><code>removeFirst()</code> Removes the first elelemts from the queue
 * </UL>
 * These are the pattern roles:
 * <UL>
 * <LI>Queue:	Context
 * <LI>QueueState: 	State interface
 * <LI>QueueEmpty: ConcreteStateA
 * <LI>QueueNormal: ConcreteStateB
 * <LI>QueueFull:	ConcreteStateC 
 * </UL>
 * This implementation passes the context as an argument to it's method 
 * calls to sate objects, thus allowing for update on demand and removing
 * the constraint that Queue has to ask the states for the successor state
 * after each call.
 *
 * According to GoF, this implementation is generally more flexible than 
 * having the state stransitions fixed in the context object. Note however
 * that this approach results in a tight coupling of ConcreteStates
 * and Context objects.
 *
 * This is the Java version.
 *
 * @author Jan Hannemann
 * @author Gregor Kiczales
 * @version 1.0, 06/13/02
 * 
 * @see QueueContext
 * @see Queue
 * @see QueueState
 * @see QueueEmpty
 * @see QueueNormal
 * @see QueueFull
 */


public class Main { 
 
 /**
 * Implements insertion into a queue. Prints out status messages.
 *
 * @param queue the queue to insert into
 * @param s the string to insert into the queue
 */ 	

	private static void testInsert(Queue queue, String s) {
		System.out.print(" Trying to insert ["+s+"] into the queue ... ");
		boolean status = queue.insert(s);
		if (status == true) {
			System.out.println("successful"); 
		} else {
			System.out.println("NOT successful, queue full?");
		}
	}

 /**
 * Implements deletion from a queue. Prints out status messages.
 *
 * @param queue the queue to insert into
 */ 	

	private static void testRemove(Queue queue) {
		System.out.print(" Trying to remove 1st element of the queue ... ");
		String item = (String) queue.getFirst(); 
		boolean status = queue.removeFirst();
		if (status == true) {
			System.out.println("successful: "+item); 
		} else {
			System.out.println("NOT successful: "+item);
		}
	}

 /**
 * Implements the driver for the State design pattern example. 
 *
 * This example of the State design pattern models a Queue ADT with
 * a limited capacity that has three different states: 
 * <UL>
 * <LI>Empty:	The queue is empty 
 * <LI>Normal: The queue is neither empty nor full
 * <LI>Full:	The queue is full (# of elements = capacity)
 * </UL>
 * The queue will store Objects to preserve generality. The following
 * operations are defined on Queue:
 * <UL>
 * <LI><code>insert(Object)</code> Inserts a new Object into the queue
 * <LI><code>getFirst():Object</code> Returns the first element in the queue
 * <LI><code>removeFirst()</code> Removes the first elelemts from the queue
 * </UL>
 * These are the pattern roles:
 * <UL>
 * <LI>Queue:	Context
 * <LI>QueueState: 	State interface
 * <LI>QueueEmpty: ConcreteStateA
 * <LI>QueueNormal: ConcreteStateB
 * <LI>QueueFull:	ConcreteStateC 
 * </UL>
 * This implementation passes the context as an argument to it's method 
 * calls to sate objects, thus allowing for update on demand and removing
 * the constraint that Queue has to ask the states for the successor state
 * after each call. 
 *
 * @param args the command line paramters, unused
 */

	public static void main(String[] args) {

		System.out.println("Testing Pattern: State - STARTING\n");
		
		Queue queue = new Queue();
		testInsert(queue, "This ");
		testInsert(queue, "is "); 
		testInsert(queue, "a ");
		testInsert(queue, "test"); 
		System.out.println();
		testRemove(queue);
		testRemove(queue);
		testRemove(queue);
		testRemove(queue);

		System.out.println("\nTesting Pattern: State - FINISHED");
	}
}

Queue.java

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QueueContext.java

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QueueEmpty.java

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QueueFull.java

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QueueNormal.java

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QueueState.java

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files.lst

2004-03-24T16:00:00Z