songcountobserver.aj

designpatterns for aop

package designpatterns.observer.aspectj;

import ca.ubc.cs.spl.aspectPatterns.patternLibrary.*;

public aspect SongCountObserver extends ObserverProtocol {
	declare parents : Song extends Subject;
	declare parents : SongPlayCounter implements Observer;

	pointcut titleUse(Song song) :
		this(song)
		&& execution(public void Song.play());

	public pointcut subjectChange(Subject subject) : 
		titleUse(Song) && this(subject);

	public void updateObserver(Subject s, Observer o) {
		SongPlayCounter counter = (SongPlayCounter) o;
		counter.incrementPlays((Song) s);
	}

	// could be injected by a dependency injection
	// framework like Spring
	private SongPlayCounter defaultCounter = new SongPlayCounter();

	pointcut songCreation(Subject s) :
		execution(public Song.new(..))
		&& this(s);

	after(Subject s) returning : songCreation(s){
		// different songs could be tracked in different statistical sets...
		addObserver(s, defaultCounter);
	}

}