import java.awt.*;
import java.applet.*;

/* <APPLET CODE=MovingCircle.class  WIDTH=100 HEIGHT=100>
   </APPLET>
*/

public class MovingCircle extends BasicAnimationApplet {

        int x, y;       // the position of the circle
        int vx;         // the horizontal velocity

        public void init() {
          x = 0;
          y = 50;
          vx = 4;
        }

        public void step() {
								int width = getSize().width; // width of applet window
                x += vx;
                if (x > width) { // wrap around
										vx = -vx;
                    x = width;
								}
								if (x < 0) {
									vx = -vx;
									x = 0;
								}
        }

        public void paint(Graphics g) {
          int size = 20;
          g.fillOval(x, y, size, size);
        }
}