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import java.util.ArrayList;
import java.util.List;
class PlayList {
private static PlayList instance;
private List<Song> list;
private PlayList() {
list = new ArrayList<Song>();
}
public static PlayList instance() {
if(instance==null ) {
instance = new PlayList();
}
return instance;
}
public void enqueue(Song song) {
list.add(song);
if(Player.instance().isIdle()) {
new Thread() {
public void run() {
System.out.println("Playing playlist...");
for (Song s : list) {
Player.instance().play(s.getName());
}
}
}.start();
}
}
}
class Song {
private String name;
public Song(String name) {
this.name = name;
}
public String getName() {
return name;
}
}
class Player {
private static Player instance;
private Player() {}
public static Player instance() {
if(instance==null ) {
instance = new Player();
}
return instance;
}
public void play(String name) {
System.out.println("Playing Song "+name+"...");
}
public boolean isIdle() {
return true;
}
}
class Jukebox {
public void play(Song song) {
Player.instance().play(song.getName());
}
}
class Main {
public static void main(String[] args) {
Song song = new Song("Merry XMas");
Jukebox jukebox = new Jukebox();
jukebox.play(song);
}
}
aspect PlaylistAspect {
void around(Song song) :
call(public void Jukebox.play(Song))
&& args(song) {
PlayList.instance().enqueue(song);
}
}
aspect CreditsAspect {
void around() : call(public void Jukebox.play(Song)) {
if(Credits.instance().enoughCredits()) {
System.out.println("Withdrawing credit.");
Credits.instance().withDraw();
proceed();
} else {
throw new InsufficientCreditsException();
}
}
}
class Credits {
private static final int INITIAL_CREDITS = 10;
private static Credits instance;
private int credits;
private Credits() {
credits = INITIAL_CREDITS;
}
public static Credits instance() {
if(instance==null ) {
instance = new Credits();
}
return instance;
}
public boolean enoughCredits() {
return credits > 0;
}
public void withDraw() {
credits--;
}
}
@SuppressWarnings("serial")
class InsufficientCreditsException extends RuntimeException {
public InsufficientCreditsException() {
super();
}
public InsufficientCreditsException(String message, Throwable cause) {
super(message, cause);
}
public InsufficientCreditsException(String message) {
super(message);
}
/**
* @param cause
*/
public InsufficientCreditsException(Throwable cause) {
super(cause);
}
}
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