Java - repaint JPanel 2 times in one method

Question

This is simple version of my problem. I have 3 classes: public class TopographyFrame extends JFrame - simple JFrame with JPAnel and button public class TopograpyPanel extends JPanel - JPanel to fill Rectangles public class Siec - class to perform calculations and call repaint on JPAnale

in JPanel i overided paintComponent() method

public void paintComponent (Graphics g) {
        super.paintComponent(g);
        Graphics2D g2 = (Graphics2D) g;
        System.out.println(rectangles.length);
        for(int i = 0 ; i < rectangles.length ; i++){
            g2.setPaint(neurony[i].winner);
            g2.fillRect((int)rectangles[i].x,(int)rectangles[i].y,(int)rectangles[i].width, (int)rectangles[i].height);
        }
    }

neurony - array of objects with field public Color winner

in class Siec i have reference to JPanel to repaint it in class JFrame i have a button with private action listener:

class MyListener implements ActionListener{
        Siec s;
        public MyListener(Siec s){
            this.s = s;
        }
        public void actionPerformed(ActionEvent arg0) {
            try {
                s.forPaint();
            } catch (Exception e) {
                e.printStackTrace();
            }
        }

method forPaint() in Siec looks like:

public void forPaint(){

        setTopography();

        try {
            Thread.sleep(3000);
        } catch (InterruptedException e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        }
        setTopography();
    }
public void setTopography() {
    for (int i = 0; i < vector.colors.length; i++) {
            neurony[i].winner = vector.colors[(int)(random() * 900 % vector.colors.length)];
    }
    panel.repaint();
}

vector.color is array of Colors

So my problem is: when i click a button i would like to JPanel repaint immediately and then after 3 second repaint one more time. Insted JPanel repaints only one time after 3s delay. }

Try to use paintImmediately(). And take a look at this: [http://stackoverflow.com/questions/4120528/repaint-in-a-loop][1] [1]: http://stackoverflow.com/questions/4120528/repaint-in-a-loop — ceklock, Apr 30 '12 at 20:40
I tried it, but paintImmediately() don't fill rectangles like i need to — viniolli, Apr 30 '12 at 20:49

score 2 · Accepted Answer · answered Apr 30 '12 at 20:31

2

You can't sleep, wait, or otherwise pause on the event handling thread, ever. Doing so blocks all events from being processed, including painting events. Your first painting can't occur because you're sleeping on the event thread, preventing it from happening.

The right way to do any kind of animation -- even simple stuff like this -- is to create your own thread. That second thread can call repaint(), sleep for 3 seconds, then call repaint() again. The SwingWorker class is nominally a simpler way to do this, but in all honesty, beginners always find creating their own thread to be easier.

answered Apr 30 '12 at 20:31

Ernest Friedman-Hill

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Thanks alot, your answer realy helped me, i changed actionPerformed(ActionEvent arg0) to: `code`public void actionPerformed(ActionEvent arg0) { new Thread(){ public void run() { try { s.forPaint(); } catch (Exception e) { e.printStackTrace(); } } }.start(); } – viniolli Apr 30 '12 at 20:44
@Ernest: Yes, that's why `EventQueue.invokeAndWait()` and `invokeLater()` throw exceptions. – wchargin Apr 30 '12 at 22:41
@WChargin -- what's that now? – Ernest Friedman-Hill May 01 '12 at 00:33
@Ernest: [If you throw `invokeAndWait` from the EDT, you get an exception](http://stackoverflow.com/questions/2435397/calling-invokeandwait-from-the-edt). I believe the same goes for `invokeLater`. – wchargin May 02 '12 at 21:55
I'm not really sure what this has to do with the discussion, but that's right, you can't call invokeAndWait() from the EDT. You can call invokeLater() though. – Ernest Friedman-Hill May 03 '12 at 00:18

score 1 · Answer 2 · answered Apr 30 '12 at 20:38

You are scheduling a repaint on the UI thread and then sleeping (blocking) the UI thread for 3seconds and then requesting another repaint again. Those two will either happen really close to each other after this method has finished (after 3 seconds) or be merged into one update (afterwards as well). Instead of sleep(3000) and then calling your setTopography again you could schedule a setTopography call on the UI thread to happen after 3 seconds.

Have a look at the Swing Timer for example: http://docs.oracle.com/javase/tutorial/uiswing/misc/timer.html

So something along the lines of:

javax.swing.Timer timer = new javax.swing.Timer(3000, new ActionListener() {
    public void actionPerformed(ActionEvent e) {
        setTopography();
    }
});
timer.setRepeats(false);
timer.start();

score 0 · Answer 3 · answered Apr 30 '12 at 20:43

Since your sleep is being performed on the Event Dispatch Thread, the repaint() event cannot be performed until the end of the wait. Do this instead:

private Timer timer = new Timer(); // use java.util.Timer

public void forPaint() {

    setTopography();

    timer.schedule(new TimerTask() {

        @Override
        public void run() {
            setTopography();
        }

    }, 3000);

}

public void setTopography() {
    SwingUtilities.invokeLater(new Runnable() {

        @Override
        public void run() {

            for (int i = 0; i < vector.colors.length; i++) {
                neurony[i].winner = vector.colors[(int)(random() * 900 % vector.colors.length)];
            }
            panel.repaint();
        }
    });
}

Keep in mind that all modifications to a Swing component (e.g. your JPanel) must happen on the EDT.

Not sure why it did not work. The concept is the same as @Ernest Friedman-Hill's solution. Perhaps someone can point out the flaw? — Nate, Apr 30 '12 at 21:21

Java - repaint JPanel 2 times in one method

3 Answers3