Fehler in Spiele Programmierung Tutorial?

Exception in thread "AWT-EventQueue-0" java.lang.ArrayIndexOutOfBoundsException: 4  
	at GamePackage.Sprite.drawObjects(Sprite.java:46)
	at GamePackage.GamePanel.paintComponent(GamePanel.java:105)
	at javax.swing.JComponent.paint(Unknown Source)
	at javax.swing.JComponent.paintToOffscreen(Unknown Source)
	at javax.swing.RepaintManager$PaintManager.paintDoubleBuffered(Unknown Source)
	at javax.swing.RepaintManager$PaintManager.paint(Unknown Source)
	at javax.swing.RepaintManager.paint(Unknown Source)
	at javax.swing.JComponent._paintImmediately(Unknown Source)
	at javax.swing.JComponent.paintImmediately(Unknown Source)
	at javax.swing.RepaintManager.paintDirtyRegions(Unknown Source)
	at javax.swing.RepaintManager.paintDirtyRegions(Unknown Source)
	at javax.swing.RepaintManager.prePaintDirtyRegions(Unknown Source)
	at javax.swing.RepaintManager.access$700(Unknown Source)
	at javax.swing.RepaintManager$ProcessingRunnable.run(Unknown Source)
	at java.awt.event.InvocationEvent.dispatch(Unknown Source)
	at java.awt.EventQueue.dispatchEventImpl(Unknown Source)
	at java.awt.EventQueue.access$200(Unknown Source)
	at java.awt.EventQueue$3.run(Unknown Source)
	at java.awt.EventQueue$3.run(Unknown Source)
	at java.security.AccessController.doPrivileged(Native Method)
	at java.security.ProtectionDomain$1.doIntersectionPrivilege(Unknown Source)
	at java.awt.EventQueue.dispatchEvent(Unknown Source)
	at java.awt.EventDispatchThread.pumpOneEventForFilters(Unknown Source)
	at java.awt.EventDispatchThread.pumpEventsForFilter(Unknown Source)
	at java.awt.EventDispatchThread.pumpEventsForHierarchy(Unknown Source)
	at java.awt.EventDispatchThread.pumpEvents(Unknown Source)
	at java.awt.EventDispatchThread.pumpEvents(Unknown Source)
	at java.awt.EventDispatchThread.run(Unknown Source)

package GamePackage;

import java.awt.Color;
import java.awt.Dimension;
import java.awt.Graphics;
import java.awt.event.KeyEvent;
import java.awt.event.KeyListener;
import java.awt.image.BufferedImage;
import java.io.IOException;
import java.net.URL;
import java.util.ListIterator;
import java.util.Vector;

import javax.imageio.ImageIO;
import javax.swing.JFrame;
import javax.swing.JPanel;

public class GamePanel extends JPanel implements Runnable, KeyListener {

	private static final long serialVersionUID = 1L;
	JFrame frame;
	
	long delta = 0;
	long last = 0;
	long fps = 0;
	
	Sprite copter;
	Vector<Sprite> actors;
	Vector<Sprite> painter;
	
	boolean up;
	boolean down;
	boolean left;
	boolean right;
	boolean started;
	int speed = 1000;
	
	public static void main(String args){
		new GamePanel(800, 600);
	}
	
	public GamePanel (int w, int h){
		this.setPreferredSize(new Dimension(w,h));
		frame = new JFrame("GameDemo");  
		frame.setLocation(100, 100);
		frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
		frame.add(this);
		frame.addKeyListener(this);
		frame.pack();
		frame.setVisible(true);
		
		doInitializations();
		
		Thread th = new Thread(this);
		th.start();
	}
	
	private void doInitializations(){
		last = System.nanoTime();
		
		BufferedImage heli = loadPics("pics/heli.gif", 4);  
		
		actors = new Vector<Sprite>();
		painter = new Vector<Sprite>();
		copter = new Sprite(heli, 400, 300, 100, this);
		actors.add(copter);
		
		started = true;
	}

	public void run(){
		while (frame.isVisible()){
			computeDelta();
			checkKeys();
			doLogic();
			moveObjects();
			cloneVectors();
			repaint();
			try{
				Thread.sleep(10);
			} catch (InterruptedException e) {}
		}
	}

	private void cloneVectors() {
		painter = (Vector<Sprite>) actors.clone();
	}

	private void computeDelta() {
		delta = System.nanoTime() - last;
		last = System.nanoTime();
		fps = ((long) 1e9)/delta;
	}
	
	@Override
	public void paintComponent(Graphics g){
		super.paintComponent(g);
		g.setColor(Color.red);
		g.drawString("FPS: " + Long.toString(fps), 20, 10);  
		
		if (!started)
			return;
		for (ListIterator<Sprite> it = painter.listIterator(); it.hasNext();){
			Sprite r = it.next();
			r.drawObjects(g);
		}
	}
	
	private void moveObjects() {
		for (ListIterator<Sprite> it = actors.listIterator(); it.hasNext();){
			Sprite r = it.next();
			r.move(delta);
		}
	}
	
	private void doLogic(){
		for (ListIterator<Sprite> it = actors.listIterator(); it.hasNext();){
			Sprite r = it.next();
			r.doLogic(delta);
		}
	}
	
	private void checkKeys(){
		if (up){
			copter.setVerticalSpeed(-speed);
		}
		if (down){
			copter.setVerticalSpeed(speed);
		}
		if (right){
			copter.setHorizontalSpeed(speed);
		}
		if (left){
			copter.setHorizontalSpeed(-speed);
		}
		if (!up && !down){
			copter.setVerticalSpeed(0);
		}
		if (!left && !right){
			copter.setHorizontalSpeed(0);
		}
	}
	
	private BufferedImage loadPics (String path, int pics){
		BufferedImage anim = new BufferedImage[pics];
		BufferedImage source = null;
		
		URL pic_url = getClass().getClassLoader().getResource(path);
		
		try{
			source = ImageIO.read(pic_url);
		} catch (IOException e){}
		
		for (int x = 0; x < pics; x++){
			anim[x] = source.getSubimage(x*source.getWidth()/pics, 0, source.getWidth()/pics, source.getHeight());
		}
		return anim;
	}

	@Override
	public void keyPressed(KeyEvent e) {
		if (e.getKeyCode() == KeyEvent.VK_UP){
			up = true;
		}
		if (e.getKeyCode() == KeyEvent.VK_DOWN){
			down = true;
		}
		if (e.getKeyCode() == KeyEvent.VK_LEFT){
			left = true;
		}
		if (e.getKeyCode() == KeyEvent.VK_RIGHT){
			right = true;
		}
	}

	@Override
	public void keyReleased(KeyEvent e) {
		if (e.getKeyCode() == KeyEvent.VK_UP){
			up = false;
		}
		if (e.getKeyCode() == KeyEvent.VK_DOWN){
			down = false;
		}
		if (e.getKeyCode() == KeyEvent.VK_LEFT){
			left = false;
		}
		if (e.getKeyCode() == KeyEvent.VK_RIGHT){
			right = false;
		}
	}

	@Override
	public void keyTyped(KeyEvent arg0) {
		// TODO Auto-generated method stub
		
	}
}

package GamePackage;

import java.awt.Graphics;
import java.awt.geom.Rectangle2D;
import java.awt.image.BufferedImage;

public class Sprite extends Rectangle2D.Double implements Drawable, Movable {

	private static final long serialVersionUID = 1L;
	long delay;
	long animation = 0;
	GamePanel parent;
	BufferedImage pics;
	int currentpic = 0;
	protected double dx;
	protected double dy;
	
	public Sprite (BufferedImage i, double x, double y, long delay, GamePanel p){
		pics = i;
		this.x = x;
		this.y = y;
		this.delay = delay;
		this.width = pics.getWidth();
		this.height = pics.getHeight();
		parent = p;
	}
	
	@Override
	public void doLogic(long delta) {
		animation += (delta/1000000);
		if (animation > delay){
			animation = 0;
			computeAnimation();
		}
	}

	private void computeAnimation() {
		currentpic++;
		if (currentpic > pics.length){
			currentpic = 0;
		}
	}

	@Override
	public void drawObjects(Graphics g) {
		g.drawImage(pics[currentpic], (int) x, (int) y, null);
	}
	
	public double getHorizontalSpeed(){
		return dx;
	}
	
	public void setHorizontalSpeed(double dx){
		this.dx = dx;
	}
	
	public double getVerticalSpeed(){
		return dy;
	}
	
	public void setVerticalSpeed(double dy){
		this.dy = dy;
	}
	
	@Override
	public void move(long delta){
		if (dx != 0){
			x += dx*(delta/1e9);
		}
		if(dy != 0){
			y += dy*(delta/1e9);
		}
	}
}