public void bounce(int numberOfBalls)    {
        int ground = 400;   // position of the ground line

        myCanvas.setVisible(true);
        ArrayList<BouncingBall> balls = new ArrayList<BouncingBall>(numberOfBalls);
        Dimension cSize = myCanvas.getSize();
        // draw the ground
        myCanvas.drawLine(50, ground, 550, ground);
        // crate and show the balls
       for(int i=0;i<numberOfBalls;i++) {
           balls.add(new BouncingBall(0, 0, 16, new Color((int)(Math.random()*Math.pow(256,3))), 24, myCanvas));
        }

       dBalls:while(true) {
            myCanvas.wait(50);          // small delay
            for (int i=0;i<numberOfBalls;i++) {
                balls.get(i).move();
                if(balls.get(i).getXPosition() >= 550) {
                    break dBalls;
                }
            }
       }
        for (int i=0;i<numberOfBalls;i++) {
            balls.get(i).erase();
       }