Screen.java

package ca.ubc.cs.spl.aspectPatterns.examples.observer.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.aspectPatterns.
 * 
 * For more details and the latest version of this code, please see:
 * http://www.cs.ubc.ca/labs/spl/projects/aodps.html
 *
 * Contributor(s):   
 */


import java.util.HashSet;
import java.util.Iterator;
 
/** 
 * Provides a means to output messages. Objects of this class act as
 * output devices. 
 *
 * @author  Jan Hannemann
 * @author  Gregor Kiczales
 * @version 1.11, 04/01/04
 */
  
public class Screen implements ChangeSubject, ChangeObserver {

    /**
     * stores the <i>Observer</i>s for this screen (<i>Subject</i>)
     */
         
    private HashSet observers;

    
    /**
     * the individual name of this screen object
     */

    private String name;
    
    /**
     * creates a new <code>Screen</code> object with the provided name.
     *
     * @param name the name for the new <code>Screen</code> object 
     */
    
    public Screen(String s) {
        this.name = s; 
        observers = new HashSet();
    }


    /**
     * Prints the name of the <code>Screen</code> object and the argument 
     * string to stdout.
     *
     * @param s the string to print
     */
     
    public void display (String s) {
	    System.out.println(name + ": " + s);
	    notifyObservers();
    }   

	/**
	 * Attaches an <i>Observer</i> to this <i>Subject</i>.
	 * 
	 * @param o the <i>Observer</i> to attach
	 */

    public void addObserver(ChangeObserver o) {
        this.observers.add(o);
    }
    
	/**
	 * Detaches an <i>Observer</i> from this <i>Subject</i>.
	 * 
	 * @param o the <i>Observer</i> to detach
	 */

    public void removeObserver(ChangeObserver o) {
        this.observers.remove(o);
    }
    
	/**
	 * Notifies all <i>Observer</i>s.
	 */
   
    public void notifyObservers() {
        for (Iterator e = observers.iterator() ; e.hasNext() ;) {
            ((ChangeObserver)e.next()).refresh(this);
        }
    }

	/**
	 * Updates an <i>Observer</i>. Uses the <i>push</i> strategy (i.e. the
	 * subject triggering the update passes itself as an argument).
	 * 
	 * This particular method prints a message showing what object caused
	 * the update 
	 *
	 * @param s the <i>Subject</i> triggering the update
	 */

    public void refresh(ChangeSubject s) { 
    	String subjectTypeName = s.getClass().getName();
    	subjectTypeName = subjectTypeName.substring(
    		subjectTypeName.lastIndexOf(".")+1, subjectTypeName.length());
        display("update received from a "+subjectTypeName+" object");
    }
        
}