problem with drawing images on JPanel

**Asido** · July 19th, 2010, 01:02 PM

So I am making a simple snake game and have this problem. The pictures just doesn't load. Can anybody tell me what I did wrong?

import java.awt.Container;
import java.awt.Graphics;
import java.awt.BorderLayout;
import java.awt.Color;
import java.awt.Image;
import java.awt.Toolkit;
import java.awt.event.KeyAdapter;
import java.awt.event.KeyEvent;
import java.awt.event.ActionListener;
import java.awt.event.ActionEvent;
 
import java.util.Random;
 
import javax.swing.JFrame;
import javax.swing.JPanel;
import javax.swing.Timer;
import javax.swing.ImageIcon;
 
class Snake extends JFrame {
	Snake(String title) {
		setTitle(title);
		setSize(300, 300);
		setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
		setVisible(true);
 
		Container c = getContentPane();
		c.setLayout(new BorderLayout());
		c.add(new Board(), BorderLayout.CENTER);
	}
 
	public static void main(String args[ ]) {
		new Snake("Snake game 2010 (c)");
	}
}
 
class Board extends JPanel implements ActionListener {
	private final int DELAY = 150;
	private final int WIDTH = 300;
	private final int HEIGHT = 300;
	private final int DOT_SIZE = 10;
	private final int ALL_DOTS_X = 30;
	private final int ALL_DOTS_Y = 30;
 
	private int x[ ] = new int[ALL_DOTS_X];
	private int y[ ] = new int[ALL_DOTS_Y];
	private int headX = x[(int)(ALL_DOTS_X / 2)];
	private int headY = y[(int)(ALL_DOTS_Y / 2)];
	private int bodyX = headX;
	private int bodyY = headY;
	private int appleX;
	private int appleY;
	private int bodySize = 3;
 
	private boolean begining = true;
	private boolean inGame = false;
	private boolean left = true;
	private boolean up = false;
	private boolean right = false;
	private boolean down = false;
	private boolean appleStatus = false;
 
	private Random random;
	private Timer timer;
	private Image apple;
	private Image head;
	private Image body;
 
	private Color backgroundColor = Color.BLACK;
 
	Board() {
		setBackground(backgroundColor);
 
		// images
		ImageIcon appleIcon = new ImageIcon(getClass().getResource("apple.png"));
		apple = appleIcon.getImage();
		ImageIcon headIcon = new ImageIcon(getClass().getResource("head.png"));
		head = headIcon.getImage();
		ImageIcon bodyIcon = new ImageIcon(getClass().getResource("body.png"));
		body = bodyIcon.getImage();
		repaint();
 
		for(int i = 0; i < (WIDTH / 10); i++)
			x[i] = i * DOT_SIZE;
		for(int i = 0; i < (HEIGHT / 10); i++)
			y[i] = i * DOT_SIZE;
 
		this.addKeyListener(new KeyAdapter() {
			public void keyPressed(KeyEvent event) {
				int keycode = event.getKeyCode();
				if(keycode == event.VK_UP && !down) {
					up = true;
					right = false;
					left = false;
					down = false;
				}
				if(keycode == event.VK_LEFT && !right) {
					left = true;
					right = false;
					up = false;
					down = false;
				}
				if(keycode == event.VK_RIGHT && !left) {
					right = true;
					left = false;
					up = false;
					down = false;
				}
				if(keycode == event.VK_DOWN && !up) {
					down = true;
					up = false;
					right = false;
					left = false;
				}
			}
		});
 
		timer = new Timer(DELAY, this);
//		timer.start();
	}
 
	void locateApple() {
		appleX = x[random.nextInt(30)];
		appleY = y[random.nextInt(30)];
	}
 
	public void paint(Graphics g) {
		super.paint(g);
		if(inGame) {
			if(!appleStatus) {
				locateApple();
				g.drawImage(apple, appleX, appleY, this);
				appleStatus = true;
			}
 
			g.drawImage(head, headX, headY, this);
			for(int i = bodySize; i == 0; i--) {
				bodyX = headX + i * DOT_SIZE;
				bodyY = headY;
				g.drawImage(body, bodyX, bodyY, this);
				begining = false;
			}
		}
	}
 
	public void actionPerformed(ActionEvent event) {
//		if(up) {
 
//		}
	}
}

**aussiemcgr** · July 19th, 2010, 01:18 PM

um, do you ever set inGame to true? Cause if not, then thats your reason.

**Asido** · July 19th, 2010, 01:33 PM

That's embarrassing. I couldn't see that for 3 hours. But unfortunately this didn't solved the problem though. I still can't see the images.
The previous code throws many NullPointerExceptions after changing inGame to true, so this is the version without Exceptions. I have no idea what is wrong here. I have examined many examples with loading images in JPanel this way. I am wondering, perhaps the paint method I am overriding doesn't belong to that JPanel?
I have tryed to load them in JLabel and then add them to JPanel. This way worked, but it is not convenient since the images has to be moved when the timer ticks.
To draw them on the JFrame worked as well, but then all the decorations would be on top of it. So not convenient again. Anyone has an idea?

import java.awt.Container;
import java.awt.Graphics;
import java.awt.BorderLayout;
import java.awt.Color;
import java.awt.Image;
import java.awt.Toolkit;
import java.awt.event.KeyAdapter;
import java.awt.event.KeyEvent;
import java.awt.event.ActionListener;
import java.awt.event.ActionEvent;
 
import java.util.Random;
 
import javax.swing.JFrame;
import javax.swing.JPanel;
import javax.swing.Timer;
import javax.swing.ImageIcon;
 
class Snake extends JFrame {
	Snake(String title) {
		setTitle(title);
		setSize(300, 300);
		setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
		setVisible(true);
 
		Board b = new Board();
		Container c = getContentPane();
		c.setLayout(new BorderLayout());
		c.add(b.panel, BorderLayout.CENTER);
	}
 
	public static void main(String args[ ]) {
		new Snake("Snake game 2010 (c)");
	}
}
 
class Board extends JPanel implements ActionListener {
	private final int DELAY = 150;
	private final int WIDTH = 300;
	private final int HEIGHT = 300;
	private final int DOT_SIZE = 10;
	private final int ALL_DOTS_X = 30;
	private final int ALL_DOTS_Y = 30;
 
	private int x[ ] = new int[ALL_DOTS_X];
	private int y[ ] = new int[ALL_DOTS_Y];
	private int headX = x[(int)(ALL_DOTS_X / 2)];
	private int headY = y[(int)(ALL_DOTS_Y / 2)];
	private int bodyX = headX;
	private int bodyY = headY;
	private int appleX;
	private int appleY;
	private int bodySize = 3;
 
	private boolean inGame = true;
	private boolean left = true;
	private boolean up = false;
	private boolean right = false;
	private boolean down = false;
	private boolean appleStatus = false;
 
	JPanel panel;
	private Random random;
	private Timer timer;
	private Image apple;
	private Image head;
	private Image body;
 
	private Color backgroundColor = Color.BLACK;
 
	Board() {
		panel = new JPanel();
		panel.setSize(WIDTH, HEIGHT);
		panel.setBackground(backgroundColor);
 
		// images
		ImageIcon appleIcon = new ImageIcon(getClass().getResource("apple.png"));
		apple = appleIcon.getImage();
		ImageIcon headIcon = new ImageIcon(getClass().getResource("head.png"));
		head = headIcon.getImage();
		ImageIcon bodyIcon = new ImageIcon(getClass().getResource("body.png"));
		body = bodyIcon.getImage();
 
		for(int i = 0; i < (WIDTH / 10); i++)
			x[i] = i * DOT_SIZE;
		for(int i = 0; i < (HEIGHT / 10); i++)
			y[i] = i * DOT_SIZE;
 
		this.addKeyListener(new KeyAdapter() {
			public void keyPressed(KeyEvent event) {
				int keycode = event.getKeyCode();
				if(keycode == event.VK_UP && !down) {
					up = true;
					right = false;
					left = false;
					down = false;
				}
				if(keycode == event.VK_LEFT && !right) {
					left = true;
					right = false;
					up = false;
					down = false;
				}
				if(keycode == event.VK_RIGHT && !left) {
					right = true;
					left = false;
					up = false;
					down = false;
				}
				if(keycode == event.VK_DOWN && !up) {
					down = true;
					up = false;
					right = false;
					left = false;
				}
			}
		});
 
		timer = new Timer(DELAY, this);
//		timer.start();
	}
 
	void locateApple() {
		appleX = x[random.nextInt(30)];
		appleY = y[random.nextInt(30)];
	}
 
	public void paint(Graphics g) {
		super.paint(g);
		if(inGame) {
			if(!appleStatus) {
				locateApple();
				g.drawImage(apple, appleX, appleY, panel);
				appleStatus = true;
			}
 
			g.drawImage(head, headX, headY, panel);
			for(int i = bodySize; i == 0; i--) {
				bodyX = headX + i * DOT_SIZE;
				bodyY = headY;
				g.drawImage(body, bodyX, bodyY, panel);
			}
		}
	}
 
	public void actionPerformed(ActionEvent event) {
//		if(up) {
 
//		}
	}
}

**copeg** · July 19th, 2010, 01:42 PM

I'd first recommend checking whether the images and ImageIcons you load are null (if's and println's work wonders for debugging). If so, then you've got a problem loading your images (make sure they are in the correct location - in your case the same directory as your .class file). If not, then you know the issue is downstream.

EDIT: I'd also recommend performing your drawing by overriding the paintComponent method rather than the paint method.

EDIT EDIT: After closer inspection, it seems you are drawing to a JPanel (Board) that is not added anywhere in your layout, whereas the Board.panel - which is added to your layout - has nothing drawn to it. Try calling:

c.add(b, BorderLayout.CENTER);//rather than b.panel

**aussiemcgr** · July 19th, 2010, 01:46 PM

Well, we need to figure out where the NullPointers are at. To do this, we either set up a bunch of try/catch statements or throw in a bunch of System.out.println's. I suggest that latter.

To place them in the correct place, we need to figure out where NullPointers could occur. That would be at the ImageIcons and the arrays as that is really the only place you set values.

Search for a null pointer when we set these. So put something like this:

ImageIcon appleIcon = new ImageIcon(getClass().getResource("apple.png"));
apple = appleIcon.getImage();
System.out.println("Apple: "+apple);
ImageIcon headIcon = new ImageIcon(getClass().getResource("head.png"));
head = headIcon.getImage();
System.out.println("Head: "+head);
ImageIcon bodyIcon = new ImageIcon(getClass().getResource("body.png"));
body = bodyIcon.getImage();
System.out.println("Body: "+body);
 
for(int i = 0; i < (WIDTH / 10); i++)
{
            x[i] = i * DOT_SIZE;
           System.out.println("i1: "+i+" Value: "+x[i]);
}
for(int i = 0; i < (HEIGHT / 10); i++)
{
            y[i] = i * DOT_SIZE;
           System.out.println("i2: "+i+" Value: "+y[i]);
}

We dont particularly care about what we get, we are just looking for any value of "null"

**aussiemcgr** · July 19th, 2010, 01:59 PM

Originally Posted by copeg

I'd first recommend checking whether the images and ImageIcons you load are null (if's and println's work wonders for debugging). If so, then you've got a problem loading your images (make sure they are in the correct location - in your case the same directory as your .class file). If not, then you know the issue is downstream.

EDIT: I'd also recommend performing your drawing by overriding the paintComponent method rather than the paint method.

EDIT EDIT: After closer inspection, it seems you are drawing to a JPanel (Board) that is not added anywhere in your layout, whereas the Board.panel - which is added to your layout - has nothing drawn to it. Try calling:

c.add(b, BorderLayout.CENTER);//rather than b.panel

You know, your on to something there, infact, the more I look at it, the more GUI problems I'm seeing.

Snake is a JFrame. So why are we calling Container c = getContentPane();? In fact, Snake doesnt even have a Container other than itself until we give it one. Maybe that is the NullPointer. And even more importantly, Board is our JPanel.

I think what we want is instead of:

Container c = getContentPane();
c.setLayout(new BorderLayout());
c.add(b.panel, BorderLayout.CENTER);

we want:

b.setLayout(new BorderLayout());
setContentPane(b);

Plus you have Board confused. You set Board to be a JPanel, but you also constructed a JPanel inside of it.

Board()
{
panel = new JPanel();
panel.setSize(WIDTH, HEIGHT);
panel.setBackground(backgroundColor);
...
}

That is probably your problem right there. You are setting Board's paint method, but not the paint method of the JPanel you created in board.
Get rid of the panel thing, and just put:

Board()
{
setSize(WIDTH, HEIGHT);
setBackground(backgroundColor);
...
}

This way, the changes we are making to the paint method will effect the JPanel our JFrame is using as the ContentPane.

**Asido** · July 19th, 2010, 02:05 PM

Originally Posted by aussiemcgr

Well, we need to figure out where the NullPointers are at. To do this, we either set up a bunch of try/catch statements or throw in a bunch of System.out.println's. I suggest that latter.

To place them in the correct place, we need to figure out where NullPointers could occur. That would be at the ImageIcons and the arrays as that is really the only place you set values.

Search for a null pointer when we set these. So put something like this:

ImageIcon appleIcon = new ImageIcon(getClass().getResource("apple.png"));
apple = appleIcon.getImage();
System.out.println("Apple: "+apple);
ImageIcon headIcon = new ImageIcon(getClass().getResource("head.png"));
head = headIcon.getImage();
System.out.println("Head: "+head);
ImageIcon bodyIcon = new ImageIcon(getClass().getResource("body.png"));
body = bodyIcon.getImage();
System.out.println("Body: "+body);
 
for(int i = 0; i < (WIDTH / 10); i++)
{
            x[i] = i * DOT_SIZE;
           System.out.println("i1: "+i+" Value: "+x[i]);
}
for(int i = 0; i < (HEIGHT / 10); i++)
{
            y[i] = i * DOT_SIZE;
           System.out.println("i2: "+i+" Value: "+y[i]);
}

We dont particularly care about what we get, we are just looking for any value of "null"

Looking at the output after doing that looks everything ok.

apple: sun.awt.image.ToolkitImage@5fcf29                                 
head: sun.awt.image.ToolkitImage@125844f                                 
body: sun.awt.image.ToolkitImage@f7c31d                                  
i1: 0 Value: 0                                                           
i1: 1 Value: 10                                                          
i1: 2 Value: 20                                                          
i1: 3 Value: 30                                                          
i1: 4 Value: 40                                                          
i1: 5 Value: 50                                                          
i1: 6 Value: 60                                                          
i1: 7 Value: 70                                                          
i1: 8 Value: 80                                                          
i1: 9 Value: 90                                                          
i1: 10 Value: 100                                                        
i1: 11 Value: 110                                                        
i1: 12 Value: 120                                                        
i1: 13 Value: 130                                                        
i1: 14 Value: 140                                                        
i1: 15 Value: 150                                                        
i1: 16 Value: 160                                                        
i1: 17 Value: 170                                                        
i1: 18 Value: 180                                                        
i1: 19 Value: 190                                                        
i1: 20 Value: 200                                                        
i1: 21 Value: 210                                                        
i1: 22 Value: 220                                                        
i1: 23 Value: 230                                                        
i1: 24 Value: 240                                                        
i1: 25 Value: 250                                                        
i1: 26 Value: 260                                                        
i1: 27 Value: 270                                                        
i1: 28 Value: 280                                                        
i1: 29 Value: 290                                                        
i2: 0 Value: 0                                                           
i2: 1 Value: 10                                                          
i2: 2 Value: 20                                                          
i2: 3 Value: 30                                                          
i2: 4 Value: 40                                                          
i2: 5 Value: 50                                                          
i2: 6 Value: 60                                                          
i2: 7 Value: 70                                                          
i2: 8 Value: 80                                                          
i2: 9 Value: 90
i2: 10 Value: 100
i2: 11 Value: 110
i2: 12 Value: 120
i2: 13 Value: 130
i2: 14 Value: 140
i2: 15 Value: 150
i2: 16 Value: 160
i2: 17 Value: 170
i2: 18 Value: 180
i2: 19 Value: 190
i2: 20 Value: 200
i2: 21 Value: 210
i2: 22 Value: 220
i2: 23 Value: 230
i2: 24 Value: 240
i2: 25 Value: 250
i2: 26 Value: 260
i2: 27 Value: 270
i2: 28 Value: 280
i2: 29 Value: 290

**aussiemcgr** · July 19th, 2010, 02:10 PM

Originally Posted by Asido

Looking at the output after doing that looks everything ok.

apple: sun.awt.image.ToolkitImage@5fcf29                                 
head: sun.awt.image.ToolkitImage@125844f                                 
body: sun.awt.image.ToolkitImage@f7c31d                                  
i1: 0 Value: 0                                                           
i1: 1 Value: 10                                                          
i1: 2 Value: 20                                                          
i1: 3 Value: 30                                                          
i1: 4 Value: 40                                                          
i1: 5 Value: 50                                                          
i1: 6 Value: 60                                                          
i1: 7 Value: 70                                                          
i1: 8 Value: 80                                                          
i1: 9 Value: 90                                                          
i1: 10 Value: 100                                                        
i1: 11 Value: 110                                                        
i1: 12 Value: 120                                                        
i1: 13 Value: 130                                                        
i1: 14 Value: 140                                                        
i1: 15 Value: 150                                                        
i1: 16 Value: 160                                                        
i1: 17 Value: 170                                                        
i1: 18 Value: 180                                                        
i1: 19 Value: 190                                                        
i1: 20 Value: 200                                                        
i1: 21 Value: 210                                                        
i1: 22 Value: 220                                                        
i1: 23 Value: 230                                                        
i1: 24 Value: 240                                                        
i1: 25 Value: 250                                                        
i1: 26 Value: 260                                                        
i1: 27 Value: 270                                                        
i1: 28 Value: 280                                                        
i1: 29 Value: 290                                                        
i2: 0 Value: 0                                                           
i2: 1 Value: 10                                                          
i2: 2 Value: 20                                                          
i2: 3 Value: 30                                                          
i2: 4 Value: 40                                                          
i2: 5 Value: 50                                                          
i2: 6 Value: 60                                                          
i2: 7 Value: 70                                                          
i2: 8 Value: 80                                                          
i2: 9 Value: 90
i2: 10 Value: 100
i2: 11 Value: 110
i2: 12 Value: 120
i2: 13 Value: 130
i2: 14 Value: 140
i2: 15 Value: 150
i2: 16 Value: 160
i2: 17 Value: 170
i2: 18 Value: 180
i2: 19 Value: 190
i2: 20 Value: 200
i2: 21 Value: 210
i2: 22 Value: 220
i2: 23 Value: 230
i2: 24 Value: 240
i2: 25 Value: 250
i2: 26 Value: 260
i2: 27 Value: 270
i2: 28 Value: 280
i2: 29 Value: 290

Then check the GUI like I suggested while you were writing this. If the problem isnt with our set variables, it must be with the GUI.

**Asido** · July 19th, 2010, 02:20 PM

I did like aussiemcgr suggested me, but now I get tons of NullPointerExceptions.

Exception in thread "AWT-EventQueue-0" java.lang.NullPointerException    
        at Board.locateApple(Snake.java:132)                             
        at Board.paint(Snake.java:140)                                   
        at javax.swing.JComponent.paintChildren(JComponent.java:862)     
        at javax.swing.JComponent.paint(JComponent.java:1038)            
        at javax.swing.JLayeredPane.paint(JLayeredPane.java:567)         
        at javax.swing.JComponent.paintChildren(JComponent.java:862)     
        at javax.swing.JComponent.paint(JComponent.java:1038)            
        at javax.swing.JComponent.paintToOffscreen(JComponent.java:5124) 
        at javax.swing.BufferStrategyPaintManager.paint(BufferStrategyPaintManager.java:278)                                                                  
        at javax.swing.RepaintManager.paint(RepaintManager.java:1224)          
        at javax.swing.JComponent._paintImmediately(JComponent.java:5072)      
        at javax.swing.JComponent.paintImmediately(JComponent.java:4882)       
        at javax.swing.RepaintManager.paintDirtyRegions(RepaintManager.java:785)
        at javax.swing.RepaintManager.paintDirtyRegions(RepaintManager.java:713)
        at javax.swing.RepaintManager.seqPaintDirtyRegions(RepaintManager.java:693)
        at javax.swing.SystemEventQueueUtilities$ComponentWorkRequest.run(SystemEventQueueUtilities.java:125)
        at java.awt.event.InvocationEvent.dispatch(InvocationEvent.java:209)
        at java.awt.EventQueue.dispatchEvent(EventQueue.java:597)
        at java.awt.EventDispatchThread.pumpOneEventForFilters(EventDispatchThread.java:269)
        at java.awt.EventDispatchThread.pumpEventsForFilter(EventDispatchThread.java:184)
        at java.awt.EventDispatchThread.pumpEventsForHierarchy(EventDispatchThread.java:174)
        at java.awt.EventDispatchThread.pumpEvents(EventDispatchThread.java:169)
        at java.awt.EventDispatchThread.pumpEvents(EventDispatchThread.java:161)
        at java.awt.EventDispatchThread.run(EventDispatchThread.java:122)

Code looks like this:

import java.awt.Container;
import java.awt.Graphics;
import java.awt.BorderLayout;
import java.awt.Color;
import java.awt.Image;
import java.awt.Toolkit;
import java.awt.event.KeyAdapter;
import java.awt.event.KeyEvent;
import java.awt.event.ActionListener;
import java.awt.event.ActionEvent;
 
import java.util.Random;
 
import javax.swing.JFrame;
import javax.swing.JPanel;
import javax.swing.Timer;
import javax.swing.ImageIcon;
 
class Snake extends JFrame {
    Snake(String title) {
        setTitle(title);
        setSize(300, 300);
        setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        setVisible(true);
 
//        Container c = getContentPane();
//        c.setLayout(new BorderLayout());
//        c.add(new Board(), BorderLayout.CENTER);
		Board b = new Board();
		b.setLayout(new BorderLayout());
		setContentPane(b);
    }
 
    public static void main(String args[ ]) {
        new Snake("Snake game 2010 (c)");
    }
}
 
class Board extends JPanel implements ActionListener {
    private final int DELAY = 150;
    private final int WIDTH = 300;
    private final int HEIGHT = 300;
    private final int DOT_SIZE = 10;
    private final int ALL_DOTS_X = 30;
    private final int ALL_DOTS_Y = 30;
 
    private int x[ ] = new int[ALL_DOTS_X];
    private int y[ ] = new int[ALL_DOTS_Y];
    private int headX = x[(int)(ALL_DOTS_X / 2)];
    private int headY = y[(int)(ALL_DOTS_Y / 2)];
    private int bodyX = headX;
    private int bodyY = headY;
    private int appleX;
    private int appleY;
    private int bodySize = 3;
 
    private boolean inGame = true;
    private boolean left = true;
    private boolean up = false;
    private boolean right = false;
    private boolean down = false;
    private boolean appleStatus = false;
 
    JPanel panel;
    private Random random;
    private Timer timer;
    private Image apple;
    private Image head;
    private Image body;
 
    private Color backgroundColor = Color.BLACK;
 
    Board() {
        setSize(WIDTH, HEIGHT);
        setBackground(backgroundColor);
 
        // images
        ImageIcon appleIcon = new ImageIcon(getClass().getResource("apple.png"));
        apple = appleIcon.getImage();
//        System.out.println("apple: " + apple);
        ImageIcon headIcon = new ImageIcon(getClass().getResource("head.png"));
        head = headIcon.getImage();
//        System.out.println("head: " + head);
        ImageIcon bodyIcon = new ImageIcon(getClass().getResource("body.png"));
        body = bodyIcon.getImage();
//        System.out.println("body: " + body);
 
        for(int i = 0; i < (WIDTH / 10); i++) {
            x[i] = i * DOT_SIZE;
//            System.out.println("i1: " + i + " Value: " + x[i]);
        }
        for(int i = 0; i < (HEIGHT / 10); i++) {
            y[i] = i * DOT_SIZE;
//            System.out.println("i2: " + i + " Value: " + y[i]);
        }
 
        this.addKeyListener(new KeyAdapter() {
            public void keyPressed(KeyEvent event) {
                int keycode = event.getKeyCode();
                if(keycode == event.VK_UP && !down) {
                    up = true;
                    right = false;
                    left = false;
                    down = false;
                }
                if(keycode == event.VK_LEFT && !right) {
                    left = true;
                    right = false;
                    up = false;
                    down = false;
                }
                if(keycode == event.VK_RIGHT && !left) {
                    right = true;
                    left = false;
                    up = false;
                    down = false;
                }
                if(keycode == event.VK_DOWN && !up) {
                    down = true;
                    up = false;
                    right = false;
                    left = false;
                }
            }
        });
 
        timer = new Timer(DELAY, this);
//      timer.start();
    }
 
    void locateApple() {
        appleX = x[random.nextInt(30)];
        appleY = y[random.nextInt(30)];
    }
 
    public void paint(Graphics g) {
        super.paint(g);
        if(inGame) {
            if(!appleStatus) {
                locateApple();
                g.drawImage(apple, appleX, appleY, this);
                appleStatus = true;
            }
 
            g.drawImage(head, headX, headY, this);
            for(int i = bodySize; i == 0; i--) {
                bodyX = headX + i * DOT_SIZE;
                bodyY = headY;
                g.drawImage(body, bodyX, bodyY, this);
            }
        }
    }
 
    public void actionPerformed(ActionEvent event) {
//      if(up) {
 
//      }
    }
}

EDIT: Finally I managed to see the images after commenting the lines (132 and 140) which throws NullPointsException!

**aussiemcgr** · July 19th, 2010, 02:29 PM

Originally Posted by Asido

I did like aussiemcgr suggested me, but now I get tons of NullPointerExceptions.

Exception in thread "AWT-EventQueue-0" java.lang.NullPointerException    
        at Board.locateApple(Snake.java:132)                             
        at Board.paint(Snake.java:140)                                   
        at javax.swing.JComponent.paintChildren(JComponent.java:862)     
        at javax.swing.JComponent.paint(JComponent.java:1038)            
        at javax.swing.JLayeredPane.paint(JLayeredPane.java:567)         
        at javax.swing.JComponent.paintChildren(JComponent.java:862)     
        at javax.swing.JComponent.paint(JComponent.java:1038)            
        at javax.swing.JComponent.paintToOffscreen(JComponent.java:5124) 
        at javax.swing.BufferStrategyPaintManager.paint(BufferStrategyPaintManager.java:278)                                                                  
        at javax.swing.RepaintManager.paint(RepaintManager.java:1224)          
        at javax.swing.JComponent._paintImmediately(JComponent.java:5072)      
        at javax.swing.JComponent.paintImmediately(JComponent.java:4882)       
        at javax.swing.RepaintManager.paintDirtyRegions(RepaintManager.java:785)
        at javax.swing.RepaintManager.paintDirtyRegions(RepaintManager.java:713)
        at javax.swing.RepaintManager.seqPaintDirtyRegions(RepaintManager.java:693)
        at javax.swing.SystemEventQueueUtilities$ComponentWorkRequest.run(SystemEventQueueUtilities.java:125)
        at java.awt.event.InvocationEvent.dispatch(InvocationEvent.java:209)
        at java.awt.EventQueue.dispatchEvent(EventQueue.java:597)
        at java.awt.EventDispatchThread.pumpOneEventForFilters(EventDispatchThread.java:269)
        at java.awt.EventDispatchThread.pumpEventsForFilter(EventDispatchThread.java:184)
        at java.awt.EventDispatchThread.pumpEventsForHierarchy(EventDispatchThread.java:174)
        at java.awt.EventDispatchThread.pumpEvents(EventDispatchThread.java:169)
        at java.awt.EventDispatchThread.pumpEvents(EventDispatchThread.java:161)
        at java.awt.EventDispatchThread.run(EventDispatchThread.java:122)

Code looks like this:

import java.awt.Container;
import java.awt.Graphics;
import java.awt.BorderLayout;
import java.awt.Color;
import java.awt.Image;
import java.awt.Toolkit;
import java.awt.event.KeyAdapter;
import java.awt.event.KeyEvent;
import java.awt.event.ActionListener;
import java.awt.event.ActionEvent;
 
import java.util.Random;
 
import javax.swing.JFrame;
import javax.swing.JPanel;
import javax.swing.Timer;
import javax.swing.ImageIcon;
 
class Snake extends JFrame {
    Snake(String title) {
        setTitle(title);
        setSize(300, 300);
        setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        setVisible(true);
 
//        Container c = getContentPane();
//        c.setLayout(new BorderLayout());
//        c.add(new Board(), BorderLayout.CENTER);
		Board b = new Board();
		b.setLayout(new BorderLayout());
		setContentPane(b);
    }
 
    public static void main(String args[ ]) {
        new Snake("Snake game 2010 (c)");
    }
}
 
class Board extends JPanel implements ActionListener {
    private final int DELAY = 150;
    private final int WIDTH = 300;
    private final int HEIGHT = 300;
    private final int DOT_SIZE = 10;
    private final int ALL_DOTS_X = 30;
    private final int ALL_DOTS_Y = 30;
 
    private int x[ ] = new int[ALL_DOTS_X];
    private int y[ ] = new int[ALL_DOTS_Y];
    private int headX = x[(int)(ALL_DOTS_X / 2)];
    private int headY = y[(int)(ALL_DOTS_Y / 2)];
    private int bodyX = headX;
    private int bodyY = headY;
    private int appleX;
    private int appleY;
    private int bodySize = 3;
 
    private boolean inGame = true;
    private boolean left = true;
    private boolean up = false;
    private boolean right = false;
    private boolean down = false;
    private boolean appleStatus = false;
 
    JPanel panel;
    private Random random;
    private Timer timer;
    private Image apple;
    private Image head;
    private Image body;
 
    private Color backgroundColor = Color.BLACK;
 
    Board() {
        setSize(WIDTH, HEIGHT);
        setBackground(backgroundColor);
 
        // images
        ImageIcon appleIcon = new ImageIcon(getClass().getResource("apple.png"));
        apple = appleIcon.getImage();
//        System.out.println("apple: " + apple);
        ImageIcon headIcon = new ImageIcon(getClass().getResource("head.png"));
        head = headIcon.getImage();
//        System.out.println("head: " + head);
        ImageIcon bodyIcon = new ImageIcon(getClass().getResource("body.png"));
        body = bodyIcon.getImage();
//        System.out.println("body: " + body);
 
        for(int i = 0; i < (WIDTH / 10); i++) {
            x[i] = i * DOT_SIZE;
//            System.out.println("i1: " + i + " Value: " + x[i]);
        }
        for(int i = 0; i < (HEIGHT / 10); i++) {
            y[i] = i * DOT_SIZE;
//            System.out.println("i2: " + i + " Value: " + y[i]);
        }
 
        this.addKeyListener(new KeyAdapter() {
            public void keyPressed(KeyEvent event) {
                int keycode = event.getKeyCode();
                if(keycode == event.VK_UP && !down) {
                    up = true;
                    right = false;
                    left = false;
                    down = false;
                }
                if(keycode == event.VK_LEFT && !right) {
                    left = true;
                    right = false;
                    up = false;
                    down = false;
                }
                if(keycode == event.VK_RIGHT && !left) {
                    right = true;
                    left = false;
                    up = false;
                    down = false;
                }
                if(keycode == event.VK_DOWN && !up) {
                    down = true;
                    up = false;
                    right = false;
                    left = false;
                }
            }
        });
 
        timer = new Timer(DELAY, this);
//      timer.start();
    }
 
    void locateApple() {
        appleX = x[random.nextInt(30)];
        appleY = y[random.nextInt(30)];
    }
 
    public void paint(Graphics g) {
        super.paint(g);
        if(inGame) {
            if(!appleStatus) {
                locateApple();
                g.drawImage(apple, appleX, appleY, this);
                appleStatus = true;
            }
 
            g.drawImage(head, headX, headY, this);
            for(int i = bodySize; i == 0; i--) {
                bodyX = headX + i * DOT_SIZE;
                bodyY = headY;
                g.drawImage(body, bodyX, bodyY, this);
            }
        }
    }
 
    public void actionPerformed(ActionEvent event) {
//      if(up) {
 
//      }
    }
}

EDIT: Finally I managed to see the images after commenting the lines (132 and 140) which throws NullPointsException!

2 things...
1) Incase you dont already know, when you get a NullPointer like that, the only one we care about is the first occurance because that is the most relevent to what we are doing. The only reason it prints out all of those NullPointers is because it is tracking it backwards because none of those methods are designed to handle exceptions.
2) What lines did you comment out that you found gives NullPointers? We cant see line numbers on your code.

**Asido** · July 19th, 2010, 02:34 PM

132:

appleX = x[random.nextInt(30)];

140:

locateApple();

The problem is I guess because paint method is called first, and then the Board constructor which initializes x and y arrays.

**copeg** · July 19th, 2010, 02:39 PM

Originally Posted by aussiemcgr

In fact, Snake doesnt even have a Container other than itself until we give it one. Maybe that is the NullPointer.

JFrame's do have an associated content pane whether it is set or not, so calling getContentPane() will not return a null pointer unless you called setContentPane(null)

Along the lines of the NullPointerException, those descriptions should lead you to the precise location of the problem, in your case line 132....(hint: where is the variable random instantiated?)

Once again, I encourage you to use paintComponent rather than paint

**aussiemcgr** · July 19th, 2010, 02:44 PM

Originally Posted by Asido

132:

appleX = x[random.nextInt(30)];

140:

locateApple();

The problem is I guess because paint method is called first, and then the Board constructor which initializes x and y arrays.

Your right, that would be the reason. We might be able to fix this though. What if you overroad the update(Graphics g) method instead of the paint(Graphics g) method? In order to prevoke that method, you would say repaint(); That way you could initialize the x and y arrays, then call repaint(); to draw the snake.

Scratch that, it may mess up real bad. Try the paintComponent suggestion copeg made. I think thats how we did it when I learned it last year.

**Asido** · July 19th, 2010, 03:07 PM

Well, thanks all you guys for the help and tips. Everything works fine and moving on with the creation.

By the way, speaking about JFrames container in Snake class, my way works fine as well:

Container c = getContentPane();
c.setLayout(new BorderLayout());
c.add(new Board(), BorderLayout.CENTER);

EDIT: If anyone is interested in the result (but I guess not

), here is the code:
I used 3 images 10x10 for the apple, head and body.

import java.awt.Container;
import java.awt.Graphics;
import java.awt.BorderLayout;
import java.awt.Color;
import java.awt.Image;
import java.awt.Font;
import java.awt.Toolkit;
import java.awt.FontMetrics;
import java.awt.event.KeyListener;
import java.awt.event.KeyEvent;
import java.awt.event.ActionListener;
import java.awt.event.ActionEvent;
 
import javax.swing.JFrame;
import javax.swing.JPanel;
import javax.swing.Timer;
import javax.swing.ImageIcon;
 
import java.util.Random;
 
class Snake extends JFrame {
	Snake(String title) {
		setTitle(title);
		setSize(310, 335);
		setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
		setVisible(true);
 
		Board b = new Board();
		Container c = getContentPane();
		c.setLayout(new BorderLayout());
		c.add(b, BorderLayout.CENTER);
//		Board b = new Board();
//		b.setLayout(new BorderLayout());
//		setContentPane(b);
	}
 
	public static void main(String args[ ]) {
		new Snake("Snake game 2010 by Asido (c)");
	}
}
 
class Board extends JPanel implements ActionListener {
	private final int WIDTH = 302;
	private final int HEIGHT = 309;
	private final int DOT_SIZE = 10;
	private final int ALL_DOTS_X = 30;
	private final int ALL_DOTS_Y = 30;
 
	private int x[ ] = new int[ALL_DOTS_X];
	private int y[ ] = new int[ALL_DOTS_Y];
	private int prevX[ ] = new int[ALL_DOTS_X * ALL_DOTS_Y];
	private int prevY[ ] = new int[ALL_DOTS_X * ALL_DOTS_Y];
	private int headX;
	private int headY;
	private int bodyX;
	private int bodyY;
	private int appleX;
	private int appleY;
	private int bodySize = 3;
	private int delay = 300;
	private int pausedDelay = 0;
	int score = 0;
 
	private boolean inGame = false;
	private boolean left = true;
	private boolean up = false;
	private boolean right = false;
	private boolean down = false;
	private boolean appleStatus = false;
 
	private Graphics g;
	private Font hugeFont = new Font("Luxi Mono", Font.BOLD, 30);
	private Font largeFont = new Font("Luxi Mono", Font.BOLD, 24);
	private Font smallFont = new Font("Luxi Mono", Font.PLAIN, 14);
	private Font tinyFont = new Font("Luxi Mono", Font.BOLD, 10);
	private Random random = new Random();
	private Timer timer;
	private Image apple;
	private Image head;
	private Image body;
 
	private Color backgroundColor = Color.BLACK;
	private Color stringColor = Color.WHITE;
 
	private MovementHandler movementHandler = new MovementHandler();
	private RestartHandler restartHandler = new RestartHandler();
 
	Board() {    	
		setSize(WIDTH, HEIGHT);
		setBackground(backgroundColor);
		setFocusable(true);//kad KeyEventai veiktu ant JPanel
 
		// images
		ImageIcon appleIcon = new ImageIcon(getClass().getResource("apple.png"));
		apple = appleIcon.getImage();
		ImageIcon headIcon = new ImageIcon(getClass().getResource("head.png"));
		head = headIcon.getImage();
		ImageIcon bodyIcon = new ImageIcon(getClass().getResource("body.png"));
		body = bodyIcon.getImage();
 
		timer = new Timer(delay, this);
        timer.start();
 
		begining();
    }
 
    void locateApple() {
        appleX = x[random.nextInt(30)];
        appleY = y[random.nextInt(30)];
 
        for(int i = 0; i < bodySize; i++) {
        	if((appleX == prevX[i] && appleY == prevY[i]) || (appleX == headX && appleY == headY))
        		locateApple();
        }
    }
 
    void begining() {
    	inGame = true;
    	left = true;
    	right = false;
    	up = false;
    	down = false;
 
    	bodySize = 3;
    	score = 0;
 
    	addKeyListener(movementHandler);
 
    	for(int i = 0; i < (WIDTH / 10); i++)
			x[i] = i * DOT_SIZE;
		for(int i = 0; i < (HEIGHT / 10); i++)
			y[i] = i * DOT_SIZE;
		locateApple();
		headX = x[((int)(ALL_DOTS_X / 2))];
		headY = y[((int)(ALL_DOTS_Y / 2))];
 
		for(int i = 0; i < bodySize; i++) {
			prevX[i] = headX + i * DOT_SIZE;
			prevY[i] = headY;
		}
 
		setTimerDelay(200);
    }
 
    void setTimerDelay(int delay) {
    	timer.setDelay(delay);
    }
 
    public void paintComponent(Graphics g) {
        super.paintComponent(g);
        if(inGame) {
            if(!appleStatus) {
                g.drawImage(apple, appleX, appleY, this);
            }
 
            g.setColor(stringColor);
            g.setFont(tinyFont);
            g.drawString("Score: " + score, 5, (HEIGHT - 1));
            g.setColor(Color.DARK_GRAY);
            g.drawLine(0, (HEIGHT - 10), WIDTH, (HEIGHT - 10));
 
            g.drawImage(head, headX, headY, this);
            for(int i = 0; i < bodySize; i++) {
                bodyX = prevX[i];
                bodyY = prevY[i];
                g.drawImage(body, bodyX, bodyY, this);
            }
 
            Toolkit.getDefaultToolkit().sync();
            g.dispose();
        }
        else 
        	gameOver(g);
    }
 
    void gameOver(Graphics g) {
    	String gameOverMessage = "Game Over";
    	String restartMessage = "Press 'R' to restart";
    	String scoreMessage = "Score: " + score;
 
    	inGame = false;
    	g.setFont(largeFont);
    	g.setColor(stringColor);
    	FontMetrics largeFM = g.getFontMetrics(largeFont);
    	g.drawString(gameOverMessage, ((WIDTH - largeFM.stringWidth(gameOverMessage)) / 2), (HEIGHT / 2));
 
    	removeKeyListener(movementHandler);
    	addKeyListener(restartHandler);
 
    	FontMetrics hugeFM = g.getFontMetrics(hugeFont);
    	g.setFont(hugeFont);
    	g.drawString(scoreMessage, ((WIDTH - hugeFM.stringWidth(scoreMessage)) / 2), (HEIGHT / 3 * 2));
    	g.setFont(smallFont);
    	g.drawString(restartMessage, 10, (HEIGHT - 20));
    }
 
    void restart() {
    	begining();
    	repaint();
 
    }
 
    void detectCollision() {
    	if(headX < 0 || headX > 290 || headY < 0 || headY > 290)
    		inGame = false;
    	if(bodySize > 3) {	
    		for(int i = 0; i < bodySize; i++) {
    			if(headX == prevX[i] && headY == prevY[i])
    				inGame = false;
    		}
    	}
    }
 
    void checkApple() {
    	if(appleX == headX && appleY == headY) {
    		bodySize++;
    		score += 100;
    		locateApple();
 
    		switch(bodySize) {
    			case 10: setTimerDelay(190); break;
    			case 15: setTimerDelay(170); break;
    			case 20: setTimerDelay(150); break;
    			case 25: setTimerDelay(140); break;
    			case 30: setTimerDelay(130); break;
    			case 35: setTimerDelay(120); break;
    		}
    	}
    }
 
    public void actionPerformed(ActionEvent event) {    	
    	for(int i = bodySize; i >= 0; i--) {
    		if(i > 0) {
    			prevX[i] = prevX[i-1];
    			prevY[i] = prevY[i-1];
    		}
    		else {
    			prevX[i] = headX;
    			prevY[i] = headY;
    		}
    	}
 
    	if(up)
        	headY -= DOT_SIZE;
    	if(down)
    		headY += DOT_SIZE;
    	if(left)
    		headX -= DOT_SIZE;
    	if(right)
    		headX += DOT_SIZE;
 
    	detectCollision();
    	checkApple();
    	repaint();
    }
 
    private class MovementHandler implements KeyListener {
    	public void keyPressed(KeyEvent event) {
    		int keycode = event.getKeyCode();
			if(keycode == KeyEvent.VK_UP && !down) {
				up = true;
				right = false;
				left = false;
				down = false;
			}
			if(keycode == KeyEvent.VK_LEFT && !right) {
               	left = true;
               	right = false;
               	up = false;
               	down = false;
            }
            if(keycode == KeyEvent.VK_RIGHT && !left) {
               	right = true;
               	left = false;
               	up = false;
               	down = false;
            }
            if(keycode == KeyEvent.VK_DOWN && !up) {
                down = true;
                up = false;
                right = false;
                left = false;
            }
    	}
 
    	public void keyReleased(KeyEvent e) {}
    	public void keyTyped(KeyEvent e) {}
    }
 
    private class RestartHandler implements KeyListener {
    	public void keyPressed(KeyEvent event) {
    		int keycode = event.getKeyCode();
    		if(keycode == KeyEvent.VK_R)
    			restart();
    	}
 
    	public void keyReleased(KeyEvent e) {}
    	public void keyTyped(KeyEvent e) {}
    }
}

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