BouncingBall.java

/*************************************************************************
 *  Compilation:  javac BouncingBall.java
 *  Execution:    java BouncingBall
 *  Dependencies: StdDraw.java
 *
 *  Assumes the following files are in the same directory:
 *     earth.gif, laser.wav, pop.wav
 *
 *  Implementation of a 2-d bouncing ball in the box from (-1, -1) to (1, 1).
 *
 *  % java BouncingBall
 *
 *************************************************************************/

import java.awt.Color;

public class BouncingBall { 
    public static void main(String[] args) {
        double rx = 0.480,  ry = 0.860;     // position
        double vx = 0.015, vy = 0.023;      // velocity

        int SIZE = 512;                     // size of graphics window
        StdDraw.create(SIZE, SIZE);
        StdDraw.setScale(-1.0, -1.0, 1.0, 1.0);

        while(true) {
            StdDraw.clear(Color.black);

            // detect collision with wall and reverse velocity
            if (Math.abs(rx + vx) > 1.0) { vx = -vx; StdDraw.play("laser.wav"); }
            if (Math.abs(ry + vy) > 1.0) { vy = -vy; StdDraw.play("pop.wav");   }

            // update position
            rx = rx + vx;
            ry = ry + vy;

            StdDraw.go(rx, ry);
            StdDraw.spot("earth.gif");
            StdDraw.pause(50);
        }
    }
}