Question

I am writing a genetic algorithm that approximates an image with a polygon. While going through the different generations, I’d like to output the progress to a JFrame. However, it seems like the JFrame waits until the GA’s while loop finishes to display something. I don’t believe it’s a problem like repainting, since it eventually does display everything once the while loop exits. I want to GUI to update dynamically even when the while loop is running.

Here is my code:

while (some conditions) {
    //do some other stuff
    gui.displayPolygon(best);
    gui.displayFitness(fitness);
    gui.setVisible(true);
}

public void displayPolygon(Polygon poly) {
    BufferedImage bpoly = ImageProcessor.createImageFromPoly(poly);
    ImageProcessor.displayImage(bpoly, polyPanel);
    this.setVisible(true);
}

public static void displayImage(BufferedImage bimg, JPanel panel) {
    panel.removeAll();
    panel.setBounds(0, 0, bimg.getWidth(), bimg.getHeight());
    JImagePanel innerPanel = new JImagePanel(bimg, 25, 25);
    panel.add(innerPanel);
    innerPanel.setLocation(25, 25);
    innerPanel.setVisible(true);
    panel.setVisible(true);
}

Answer 1

I think your problem is that Java won’t let you update the GUI from another thread than the GUI thread itself. This causes grief to everybody at some point, but fortunately a reasonably convenient workaround is provided.

The idea is to pass the code that does the updating as a Runnable to the method SwingUtilities.invokeAndWait or SwingUtilities.invokeLater. Here’s an example.

To run your GA at maximum speed and exploit parallelism, I guess invokeLater would be appropriate.

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EDIT: Oh wait, camickr’s solution hints that you’re doing something else: You’re running the GA in the GUI’s thread. Well, that can only do one or the other, calculate or display. So the true solution would combine both changes:

1. Run the GA in a separate thread (you could run it in the thread used by main() after you’ve instantiated the GUI); and
2. Use invokeLater to communicate updates to the GUI thread (which camickr calls the EDT, or Event Dispatch Thread).