null pointer exception...

[Jeffrey Chu]

 import java.awt.*;
import java.awt.event.*;
import javax.swing.*;
import javax.swing.event.*;
 
public class Scene extends JApplet {
 
private BigButtonPanel panel1;
private ImagePanel panel2;
private int panelchoice = 0, x = 0;
 
public void init ( )  {
setBackground ( Color.black );
Container contentPane = getContentPane();
        contentPane.setLayout ( new GridLayout ( 3, 1));
   
panel1 = new BigButtonPanel ( );
        contentPane.add ( panel1 );
 
panel2 = new ImagePanel ( );
        contentPane.add ( panel2 );

}
 
public Insets getInsets ( ) {
return new Insets ( 5, 5, 5, 5 );
}
  
class BigButtonPanel extends JPanel implements ActionListener   {
 
public BigButtonPanel ( )   {
setLayout(new BorderLayout());
setBackground ( Color.cyan );
       JButton big = new JButton ( " Sun " );
       big.addActionListener ( this );  
       this.add ( big );
setBackground ( Color.blue );
       JButton small = new JButton ( " Snow " );
       small.addActionListener ( this );  
       this.add ( small );
}
 
   public void actionPerformed ( ActionEvent evt ) {
      String command = evt.getActionCommand();
               
      if ( command.equals ( " Snow " ) )   {
         panelchoice = 1;
panel2.repaint ( );
}
else if ( command.equals ( " Sun " ) )   {
         panelchoice = 2;
panel2.repaint ( );
}
}
}
 
 
class ImagePanel extends JPanel implements ChangeListener {
JSlider bottom;
private Image [] image;
public ImagePanel ( )   {
this.setLayout ( new BorderLayout ( ) );
 
image[1] = getImage ( getDocumentBase ( ), "penguin.jpg" );
WaitForImage ( this, image[1] );

image[2] = getImage ( getDocumentBase ( ), "background.jpg" );
WaitForImage ( this, image[2] );

 
       bottom = new JSlider ( JSlider.HORIZONTAL, 0, 600, 600 );
       this.add ( bottom, BorderLayout.SOUTH );
       bottom.addChangeListener ( this );
 
}
 
public void WaitForImage ( JPanel component, Image image )   {
MediaTracker tracker = new MediaTracker ( component );
try  {
tracker.addImage ( image, 0 );
tracker.waitForID ( 0 );
}
catch ( InterruptedException e )   {
e.printStackTrace ( );   
}
}
 
public void paintComponent ( Graphics g ) {
super.paintComponent ( g );
//paints the background
g.drawImage ( image[2], 0, 0, 600, 500, this );
//paints a penguin
g.drawImage ( image[1], x, x-100, 90, 100, this );
//if panel choice is 1 it paints snow
if ( panelchoice == 1 )  {
g.setColor ( Color.white );
for ( int i = 0; i < 200; i++ )   {
int x = (int)(Math.random() * 600);
int y = (int)(Math.random() * 500);
g.fillOval ( x, y, 6, 6 );
}
}
//if panel choice is 2, then it paints a sun
else if (panelchoice == 2){
g.setColor(Color.yellow);
g.fillOval(0,0,50,50);
}
}
 
   public void stateChanged ( ChangeEvent evt )   {
       x = bottom.getValue();
this.repaint ( );
   }
}
} 

i've looked at the code my self but i cant see to pin point the problem
[ May 08, 2005: Message edited by: Jeffrey Chu ]

[K Riaz]

private Image [] image;
public ImagePanel ( )   {
this.setLayout ( new BorderLayout ( ) );
 
image[1] = getImage ( getDocumentBase ( ), "penguin.jpg" );
WaitForImage ( this, image[1] );

image[2] = getImage ( getDocumentBase ( ), "background.jpg" );
WaitForImage ( this, image[2] );
 

In Java, you must allocate space for an array using the "new" keyword with its size. In your case, you have an array of type "image", but have not correctly intialized it. Change the offending line to:

 
//Create an array with two elements
private Image [] image = new Image[2];

Try that.

[K Riaz]

Just one more thing, you will get an ArrayIndexOutOfBounds exception. Array indexes begin from 0, not 1. So use "image[0]=.." and "image[1]=..".
[ May 08, 2005: Message edited by: Kashif Riaz ]

[Jeffrey Chu]

ok i did a rework of my code, but now i get this error...

java.lang.NullPointerException
at sun.java2d.SunGraphics2D.drawImage(SunGraphics2D.java:2721)
at sun.java2d.SunGraphics2D.drawImage(SunGraphics2D.java:2682)
at Scene$DisplayPanel.paintComponent(Scene.java:59)
at javax.swing.JComponent.paint(JComponent.java:808)
at javax.swing.JComponent.paintChildren(JComponent.java:647)
at javax.swing.JComponent.paint(JComponent.java:817)
at javax.swing.JComponent.paintChildren(JComponent.java:647)
at javax.swing.JComponent.paint(JComponent.java:817)
at javax.swing.JLayeredPane.paint(JLayeredPane.java:557)
at javax.swing.JComponent.paintChildren(JComponent.java:647)
at javax.swing.JComponent.paintWithOffscreenBuffer(JComponent.java:4794)
at javax.swing.JComponent.paintDoubleBuffered(JComponent.java:4740)
at javax.swing.JComponent.paint(JComponent.java:798)
at java.awt.GraphicsCallback$PaintCallback.run(GraphicsCallback.java:21)
at sun.awt.SunGraphicsCallback.runOneComponent(SunGraphicsCallback.java:60)
at sun.awt.SunGraphicsCallback.runComponents(SunGraphicsCallback.java:97)
at java.awt.Container.paint(Container.java:1312)
at sun.awt.RepaintArea.paint(RepaintArea.java:177)
at sun.awt.windows.WComponentPeer.handleEvent(WComponentPeer.java:260)
at java.awt.Component.dispatchEventImpl(Component.java:3678)
at java.awt.Container.dispatchEventImpl(Container.java:1627)
at java.awt.Component.dispatchEvent(Component.java:3477)
at java.awt.EventQueue.dispatchEvent(EventQueue.java:456)
at java.awt.EventDispatchThread.pumpOneEventForHierarchy(EventDispatchThread.java:201)
at java.awt.EventDispatchThread.pumpEventsForHierarchy(EventDispatchThread.java:151)
at java.awt.EventDispatchThread.pumpEvents(EventDispatchThread.java:145)
at java.awt.EventDispatchThread.pumpEvents(EventDispatchThread.java:137)
at java.awt.EventDispatchThread.run(EventDispatchThread.java:100)

and my enw code is

 import java.awt.*;
import java.awt.event.*;
import javax.swing.*;
import javax.swing.event.*;
 
public class Scene extends JApplet  {
 
private int x, canvaschoice;
private DisplayPanel canvas;
private ButtonPanel buttonPanel;
private Image [] image = new Image[2];
private JSlider bottom;

 
public Scene ( )   {
x = 0;
canvaschoice = 0;
}
 
public void init() {
      setBackground(Color.gray);
 
canvas = new DisplayPanel();
getContentPane().add ( canvas, BorderLayout.CENTER );
 
       buttonPanel = new ButtonPanel ( );
       getContentPane().add ( buttonPanel, BorderLayout.NORTH );

image = new Image[4];

}

class DisplayPanel extends JPanel implements ChangeListener  {
 
public DisplayPanel ( )   {
setBackground ( Color.darkGray );
for ( int i = 0; i < image.length; i++ )   {
image[i] = getImage ( getDocumentBase ( ), "" + i + ".jpg" );
WaitForImage ( this, image[i] );
}
bottom = new JSlider ( JSlider.HORIZONTAL, 0, 600, 600 );
this.add ( bottom, BorderLayout.SOUTH );
bottom.addChangeListener ( this );
}
public void WaitForImage ( JPanel component, Image image )   {
MediaTracker tracker = new MediaTracker ( component );
try  {
tracker.addImage ( image, 0 );
tracker.waitForID ( 0 );
}
catch ( InterruptedException e )   {
e.printStackTrace ( );   
}
}
 
public void paintComponent(Graphics g) {
super.paintComponent ( g );
//paints the background
g.drawImage ( image[1], 0, 0, 600, 500, this );
//paints a penguin
g.drawImage ( image[0], x, x-100, 40, 60, this );
//if panel choice is 1 it paints snow
if ( canvaschoice == 1 )  {
g.setColor ( Color.white );
for ( int i = 0; i < 200; i++ )   {
int x = (int)(Math.random() * 600);
int y = (int)(Math.random() * 500);
g.fillOval ( x, y, 6, 6 );
}
}
//if panel choice is 2, then it paints a sun
else if (canvaschoice == 2){
g.setColor(Color.yellow);
g.fillOval(0,0,50,50);
}
}
public void stateChanged ( ChangeEvent evt )   {
       x = bottom.getValue();
canvas.repaint ( );
   }
}
 



class ButtonPanel extends JPanel implements ActionListener   {
 
public ButtonPanel ( )   {
setBackground ( Color.black );
       
       JButton snowButton = new JButton ( "Snow" );
       snowButton.addActionListener ( this );  
       this.add ( snowButton );
 
       JButton sunButton = new JButton ( "Sun" );
       sunButton.addActionListener ( this );
       this.add ( sunButton );
 
       JButton resetButton = new JButton ( "Reset" );
       resetButton.addActionListener ( this );
       this.add ( resetButton );
 
}
 
   public void actionPerformed ( ActionEvent evt ) {
      String command = evt.getActionCommand();
               
      if ( command.equals ( "Snow" ) )
         canvaschoice = 1;
      else if ( command.equals ( "Sun" ) )
         canvaschoice = 2;
      else if ( command.equals ( "Reset" ) ){
         canvaschoice=0;
canvas.repaint();
}
      }
}
}
 
 

[Layne Lund]

Most of the classes listed in the stack trace you gave are from the Java API. You don't have any direct control over those. However, there is one line that says "Scene$DisplayPanel.paintComponent(Scene.java:59)". This looks promising. It indicates that the problem originated in your Scene.java file on line 59. This is in the paintComponent() method of your DisplayPanel class (which happens to be an inner class of Scene). So which line is #59? I could probably figure it out from the context given in the stack trace, but I thought I'd let you look at it for a minute. If you are still stuck, tell us which line this is referring to and we'll help from there.

Layne

[Jeffrey Chu]

well i know its refering to g.drawImage ( image[1], 0, 0, 600, 500, this );
but i have that image on my computer.... i have no clue....