JAVA - How to create new thread every mouse click

Question

In java, how do you drop a ball to a panel in every mouse click? Say I clicked the panel 3 times, so there should be 3 balls bouncing in the panel.

I have this code block:

ball = new Thread() {
    public void run() {
        while (true) { 
            x += speedX;
            y += speedY;
        }
    }
};
ball.start();

repaint();
try {Thread.sleep(100/3);}catch(InterruptedException ex){}

And the method to paint the ball:

public void paintComponent(Graphics ball) {
  super.paintComponent(ball);
  if(clicks>0){
    ball.setColor(Color.BLUE);
    ball.fillOval((int) (x - rad), (int) (y - rad), (int)(2 * rad), (int)(2 * rad));
  }
}

But this thread only drops 1 ball in the panel. I also did try an array of threads but it did not work.

Answer 1

1. Obviously you need to keep different (x,y) data for each ball, eg have a class Ball with x,y and then List<Ball>

(unless you meant to have them calculated, namely have a single x,y with the balls calculated in some offset to it)

2. on paintComponent you need to paint all balls, which means some loop of 'fillOval'

3. your thread(s) need to call ' repaint ' after changing x and y. It also needs some ' sleep ' otherwise the ball will run too fast.

4. Regarding the threads, I kind of agree with MadProgrammer: you could have a single thread that iterates over all balls and advances their coordiantes. But it you want several threads (for the exercise, or for better future control) it should work fine, as long as each threads knows which ball it's responsible for. So it's something like

    List<Ball> balls= ...; Class BallRunnable implements Runnable{ private Ball ball; private JComponent comp; // the one whose paintComponent does fillOval public BallRunnable(Ball ball, JComponent comp){ this.ball=ball; } public void run(){ while(true){ ball.x +=speedX; ball.y+= speedY; Thread.sleep(200); comp.repaint(); } } } 

Answer 2

The behavior of the panel must be defined by setting a MouseListener to the panel to launch a new thread which would create a new ball.

    final JPanel p = new JPanel();
    p.addMouseListener(new MouseListener() {
        @Override
        public void mouseClicked(MouseEvent e) {
            Thread ball = new Thread() {
                public void run() {
                    while (true) {
                        x += speedX;
                        y += speedY;
                    }
                }
            };
            ball.start();

            p.repaint();
        }

        @Override
        public void mousePressed(MouseEvent e) {

        }

        @Override
        public void mouseReleased(MouseEvent e) {

        }

        @Override
        public void mouseEntered(MouseEvent e) {

        }

        @Override
        public void mouseExited(MouseEvent e) {

        }
    });