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

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

public class MovingCircles extends BasicAnimationApplet {

        CircleSprite[] circles = new CircleSprite[10];

        public void init() {
                int width = 100;    // width of applet's window
                int height = 100;   // height of applet's window

                for (int i = 0; i < circles.length; i++) {
                        int x = randomIntBelow(width);
                        int y = randomIntBelow(height);
                        Color c = randomColor();
                        circles[i] = new CircleSprite(x, y, c);
                      }
                    }

        public void step() {
                for (int i = 0; i < circles.length; i++)
                        circles[i].step();
        }

        public void paint(Graphics g) {
                for (int i = 0; i < circles.length; i++)
                        circles[i].paint(g);
        }

        Color randomColor() {
                Color[] colors = {Color.blue, Color.red, Color.green, Color.yellow};
                int r = randomIntBelow(colors.length);
                return colors[r];
  }

  int randomIntBelow(int n) {
    // Return a random number between 0 and one less than n.
    return (int) (Math.random() * n);
  }


}
      

class CircleSprite {
        int x, y;           // the position of the circle
        int vx, vy;         // the velocity
        Color color;

        CircleSprite(int  xx, int yy, Color clr) {
                this.x = xx;
                this.y = yy;
                this.color = clr;
                vx = 2;
                vy = 0;
        }

        void step() {
          int width = 100;
          int height = 100;
          x += vx;
          y += vy;
          // wrap in all four directions
          if (x > width)
            x = 0;
          if (x < 0)
            x = width;
          if (y > height)
            y = 0;
          if (y < 0)
            y = height;
        }

        void paint(Graphics g) {
          int size = 10;
          g.setColor(color);
          g.fillOval(x, y, size, size);
        }
      }