package designpatterns.observer.java;import java.util.ArrayList;import java.util.List;public class ObserverClient {	public static void main(String[] args) {		BillingService basicBilling = new BillingService();		BillingService premiumBilling = new BillingService();				Song song = new Song("Kris Kringle Was A Cat Thief");		song.addObserver(basicBilling);						Song song2 = new Song("Rock n Roll McDonald's");		song2.addObserver(basicBilling);		//this song is billed by two services,		//perhaps the label demands an premium for online access?		song2.addObserver(premiumBilling);				Playlist favorites = new Playlist("Favorites");		favorites.addObserver(basicBilling);				List songs = new ArrayList();		songs.add(song);		songs.add(song2);		favorites.setSongs(songs);				favorites.play();				song.showLyrics();	}}