When to repaint panel?

Question

I'm having a problem figuring out when exactly my panel is ready to be repainted. Inside this JPanel I'm loading Images and then drawing them with paintComponent. My problem is that when the panel is first painted, these images aren't loaded yet so paintComponent can't draw them. However, after a second or so these images are loaded and if I force a repaint by resizing the window everything shows up fine.
What's the best way to repaint the panel when the Images are loaded? I tried a thread approach but I was running into problems where for some reason the images would never load (as if the thread was taking over the whole program) and I would like to avoid threads if possible. Any suggestions would be greatly appreciated.

Answer 1

Synchronous loading means that your application stops everything until the image is fully-loaded, then continues on its way. Asynchronous loading means the app moves ahead without loading the image; not a desirable thing. The old boiler plate method for synchronous loading is with a MediaTracker. The newer way is with ImageIO but this requires j2se 1.4 or later. If you will load or initiate the loading of your images in the constructor of your app/component they will be ready when the app/component is first painted.
class AnImageComponent extends JPanel
    BufferedImage/Image image;
    public AnImageComponent()
        loadImage();
    protected void paintComponent(Graphics g)
        g.drawImage(image, x, y, this);
    private void loadImage()
        // synchronously load image...
}The override of the 'update' method is not recommended and usually not necessary in Swing. Calling 'repaint' and/or 'validate/revalidate' for updating gui components is usually done from within event code, eg, from within the actionPerformed method of a SwingTimer, a while loop inside an animation thread, or a ui component event listener.