RotatingBall.java

/*************************************************************************
 *  Compilation:  javac RotatingBall.java
 *  Execution:    java RotatingBall
 *  Dependencies: StdDraw.java
 *
 *  Assumes the following files are in the same directory: earth.gif.
 *
 *  Implementation of a 2-d bouncing and rotating ball.
 *
 *  % java RotatingBall
 *
 *************************************************************************/

import java.awt.Color;

public class RotatingBall { 
    public static void main(String[] args) {
        double rx = 0.4,  ry = 0.6;        // position
        double vx = 0.02, vy = 0.03;       // velocity
        double spin = 20;                  // spin this many degrees

        int SIZE = 512;                    // size of window
        StdDraw.create(SIZE, SIZE);
        StdDraw.setScale(0, 0, 1, 1);

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

            // detect collision with wall and reverse velocity
            if ((rx + vx > 1) || (rx + vx < 0.0)) { vx = -vx; }
            if ((ry + vy > 1) || (ry + vy < 0.0)) { vy = -vy; }

            // update position
            rx = rx + vx;
            ry = ry + vy;
            StdDraw.go(rx, ry);
            StdDraw.rotate(spin);
            StdDraw.spot("earth.gif");
            StdDraw.pause(50);
        }
    }
}