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.
}

Answer 1

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.