.getGraphics in custom rendering method returns null... anyone know why?

Question

Hello,
The problem is pretty much exactly as specified.
Take this class for example:
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package vicsanimation;
* @author
import java.awt.*;
import java.awt.image.*;
import javax.imageio.*;
import java.io.*;
import javax.swing.*;
public class VButton extends JLabel {
    BufferedImage activeImage;
    BufferedImage pressedImage;
    BufferedImage deactiveImage;
    BufferedImage highlightedImage;
    ImageIcon currentImage;
    public VButton (String b1, String b2, String b3, String b4, int x, int y){
        activeImage = new BufferedImage(1,1,BufferedImage.TYPE_INT_ARGB);
        try { 
            activeImage = ImageIO.read(new File(b1));
            pressedImage = ImageIO.read(new File(b2));
            deactiveImage = ImageIO.read(new File(b3));
            highlightedImage = ImageIO.read(new File(b4));
        catch (IOException e) {
            System.out.println(e.getMessage());
        this.setSize(activeImage.getWidth(), activeImage.getHeight());
        this.setLocation(x,y);
        this.setVisible(true);
        this.render();      // <----------------- ERROR FROM HERE!!!
    // This is the method used to render the button. It does not use the paint method
    // because the application can use FullScreen mode.
    public void render(){
        Graphics2D buttonGraphics = (Graphics2D)this.getGraphics();
            buttonGraphics.drawImage(activeImage, null, 0, 0);
            System.out.println("Image drawn successfully");
}If I run this code, I get a Null-Pointer exception thrown from the last method. This is because the "buttonGraphics" object is null.
I do know a work-around, although I'd really like to know exactly why this is happening.
The work-around is simply to remove the this.render() call at the end of the constructor, create the button in an outside container object, and then call the render() method from the object that contains the button. For example:
    private void initScreen(){
        ..... snip ....
        VButton closeButton = getCloseButton();
        this.add(closeButton);
        closeButton.render();
        ..... snip .....
    }If anyone could explain to me why this happens (in non-Java expert language) I'd be very thankful.

Answer 1

Thanks again for your help.
I'm sure the solution to every problem is in the API if one were to look hard enough!
But obviously the API is massive and I suppose you learn these things from experience more than committing that kind of stuff to memory. If I were to scour the API looking for solutions to things which I only barely understand to start with I'd go mad. Let alone be there for several days.
So thanks for helping out, I really appreciate it!
Edited by: wombatvvv on Jul 23, 2008 3:23 PM