Clock applet example. createImage returns null

Question

Hello, I'm quite new with AWT and I need help. I cannot use swing.
I'm trying to make a "normal" app with the applet of the analog clock that is included as an example in the JDK. I have been reading the API of java.awt.applet and I have made the following things:
1.- I have deleted the Parser classes that are there fore taking the parameters that were used in the html.
2.- I have made an class that extends Panel and implement Runnable, as same as the class Applet. This class, called XClock, includes an adapted AnalogClock that is the class included in the example.
I think I have to do the double-buffering. So I have included the following code:
// Create the offImage for double-buffering.
offImage = createImage(size.width, size.height);
offG = offImage.getGraphics();
Of course, size has the right values. My code compiles ok, but when I run it says that offImage becomes null, so in the second line it throws a NullPointerException.
I have made the following class to test the XClock class:
public class Prueba {
public static void main(String[]args){
XClock reloj=new XClock();
XClock extends Panel. �Any help?. Please, it's quite important for me.

Answer 1

This will make you go:
import java.awt.event.*;
import java.awt.*;
public class Prueba  extends Frame 
     Xclock clock = new Xclock();
public Prueba ()
     addWindowListener(new WindowAdapter()
    {     public void windowClosing(WindowEvent ev)
          {     setVisible(false);
     setBounds(10,10,400,300);
     add(clock);
     setVisible(true);
public class Xclock extends Panel
     Image    offImage = null;
     Graphics offG;
public Xclock()
public void paint(Graphics g)
     if (offImage == null)
          offImage = createImage(getWidth(),getHeight());
          offG     = offImage.getGraphics();
          offG.drawOval(10,10,250,250);
     g.drawImage(offImage,0,0,this);
public void update(Graphics g)
     paint(g);
public static void main(String[] args )
     new Prueba ();
Noah
import java.awt.event.*;
import java.awt.*;
public class Prueba extends Frame
     Xclock clock = new Xclock();
public Prueba ()
     addWindowListener(new WindowAdapter()
{     public void windowClosing(WindowEvent ev)
          {     setVisible(false);
     setBounds(10,10,400,300);
     add(clock);
     setVisible(true);
public class Xclock extends Panel
     Image offImage = null;
     Graphics offG;
public Xclock()
public void paint(Graphics g)
     if (offImage == null)
          offImage = createImage(getWidth(),getHeight());
          offG = offImage.getGraphics();
          offG.drawOval(10,10,250,250);
     g.drawImage(offImage,0,0,this);
public void update(Graphics g)
     paint(g);
public static void main(String[] args )
     new Prueba ();
}