Issue with Java join() method.

Question

First of all here are some code snippets:

public void startThread() {
    this.animationThread = new Thread(this);
    this.animationThread.start();
    try {
        this.animationThread.join();
    } catch (InterruptedException e) {
        e.printStackTrace();
    }
}

@Override
public void run() {     
    pirateMainAnimation.animate();
}

public void animate() {
    for (int j = 0; j < 9; j++) {
        try {
            Thread.sleep(250);
        } catch (InterruptedException e) {
            break;
        }
        PirateAnimationPanel.getInstance().setCurrent(j);
        PirateAnimationPanel.getInstance().repaint();
    }
}

I'm trying to animate some images. The thing is that I want the main thread to wait for the animation thread to finish and then to continue. I searched around, read a little bit and decided to use the join() method. It perfectly waits for the thread to finish but I doesn't animate correctly. The repaint() method gets called 2 times instead of nine. I think maybe the problem is because I used singletons. Here is the singleton implementation.

import java.awt.Graphics;
import java.awt.MediaTracker;

import javax.swing.JPanel;

import uk.ac.aber.dcs.piratehangman.animation.PirateMainAnimation;
import uk.ac.aber.dcs.piratehangman.utilityclasses.AnimationThread;

@SuppressWarnings("serial")
public class PirateAnimationPanel extends JPanel {
    private int current;
    private MediaTracker mTracker;
    private PirateMainAnimation pirateMainAnimation;
    private AnimationThread animationThread;

    private PirateAnimationPanel() {
        this.current = 0;
        this.pirateMainAnimation = new PirateMainAnimation();
        mTracker = new MediaTracker(this);
        this.animationThread = new AnimationThread();
        setMediaTracker();
        repaint();
    }

    private void setMediaTracker() {
        for (int i = 0; i < 9; i++) {
            mTracker.addImage(
                    this.pirateMainAnimation.getImagesForAnimation()[i],
                    this.pirateMainAnimation.getImagesForAnimationID()[i]);
            try {
                mTracker.waitForID(this.pirateMainAnimation
                        .getImagesForAnimationID()[i]);
            } catch (InterruptedException e) {
                System.out.println("Error loading image: " + i);
            }
        }
    }

    public void playAnimation() {
        this.animationThread.startThread();
    }

    public void paintComponent(Graphics g) {
        super.paintComponents(g);
        System.out.println("called");
        g.drawImage(this.pirateMainAnimation.getImagesForAnimation()[current],
                0, 0, this);
    }

    private static class PirateAnimationPanelHolder {
        private static final PirateAnimationPanel pirateAnimationPanel =
            new PirateAnimationPanel();
    };

    public static PirateAnimationPanel getInstance() {
        return PirateAnimationPanelHolder.pirateAnimationPanel;
    }

    public void setCurrent(int current) {
        this.current = current;
    }

    public int getCurrent() {
        return current;
    }
}

Answer 1

I think you mean that the paintComponent() methods only gets called twice. Also I think you should be able to remove the call to super.paintComponents() if you fill the component to the background color.

The repaint() method only marks the component as dirty and requests a re-render on the next paint.

I would have expected the Swing thread to be able to repaint within the 250ms but I'm not sure what other work is being done/rendered. You might want to put a call to MediaTracker.waitForAll() before the animation.

While the static singleton is not adding much I don't think it is causing a problem (in this case).

Update: So the problem is that the join() is on the Swing event Thread which is blocking the repainting of the component. I suggested a call like the following to show the "new game dialog after the last animation:

SwingUtilities.invokeLater(new Runnable() {
    public void run() { showDialog(); }
})

Answer 2

"Note that events being posted to the EventQueue can be coalesced," which may explain the disparity. Also, be certain to build your GUI on event dispatch thread. See A More Complex Image Icon Example for a more detailed discussion.

Addendum: Improving Perceived Performance When Loading Image Icons has a nice SwingWorker example that may simplify the off-loading.