Question

I’m stuck with a problem considering my Display class, which extends Canvas.
A single thread is running within the very same class.
In this thread, the repaint method is called.
However, while the thread works fine, the paint method is never called!

Here’s my code (I left out everything unrelated):

package display;

public final class Display extends Canvas implements Runnable {
private static final long serialVersionUID = 1L;

private Frame frame;

private GraphicsEnvironment ge;
private GraphicsDevice gd;

public BDisplay() {     
    ge = GraphicsEnvironment.getLocalGraphicsEnvironment();
    gd = ge.getDefaultScreenDevice();

    frame = new Frame();

    //frame.setUndecorated(true);
    frame.setLocationRelativeTo(null);
    frame.setResizable(false);
    frame.setVisible(true);

    frame.add(this);

    frame.setLayout(null);

    //gd.setFullScreenWindow(frame);
}

@Override
public final void paint(Graphics g) {
    //THIS METHOD IS NEVER CALLED

    System.out.println("Paint method was called!");
    super.paint(g);

    //...
}

@Override
public synchronized void run() {
    while (isRunning()) {
        //THIS LOOP WORKS FINE.
        this.repaint();
    }
}
}

It has nothing to do with some missing functions like isRunning().
They exist, i just left those out.

I never stumbled across a problem like this before,
although I haven’t done anything with SWING or AWT for some time now.

Can anyone help?

The thread loop works fine,
but the repaint just doesn’t seem to get scheduled…

Answer 1

You’re realizing the JFrame before you add the component (i.e. Canvas, and previously JPanel).

Try this

public BDisplay() {     
    ge = GraphicsEnvironment.getLocalGraphicsEnvironment();
    gd = ge.getDefaultScreenDevice();

    frame = new Frame();
    frame.setResizable(false);
    frame.add(this);
    //frame.setLayout(null); // Why are you using a null layout?
    frame.pack();
    frame.setLocationRelativeTo(null);
    frame.setVisible(true);
}

EDIT

By the way, I’d recommend using a JPanel instead of a Canvas since it’s not recommended that you mix heavy and light components. For more detail, see Mixing heavy and light components.