/**

     * Simulate several bouncing balls

     */

    public void bounce(int numPelotas)

    {

        int ground = 400;   // position of the ground line

        ArrayList<BouncingBall> pelotas = new ArrayList<BouncingBall>();


        myCanvas.setVisible(true);


        // draw the ground

        myCanvas.drawLine(50, ground, 550, ground);


        // crate and show the balls

        for (int i = 0; i < numPelotas; i++) {

            pelotas.add(new BouncingBall(50+(i*60), 50, 16, Color.blue, ground, myCanvas));

            pelotas.get(i).draw();

        }


        // make them bounce

        boolean finished =  false;

        int aux = 0;

        while(!finished) {

            myCanvas.wait(50);           // small delay

            for(BouncingBall pelota : pelotas) {

                pelota.move();

            }

            // stop once ball has travelled a certain distance on x axis

            for (BouncingBall pelota : pelotas){

                if (pelota.getXPosition() >= 550){

                    aux ++;               

                } 

            }

            if (aux==numPelotas-1) {

                finished = true; 

            }

        }

        for(int i=0; i<numPelotas; i++) {

            pelotas.get(i).erase();

        }

    }