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

public class Ball extends Applet 
{
    private int x = 7,xChange = 7;
    private int y = 2,yChange = 2;
    private int diameter = 10;

    private int rectLeftX = 0,rectRightX = 100;
    private int rectTopY = 0,rectBottomY = 100;

    public void paint(Graphics g)
    {
        g.drawRect(rectLeftX,rectTopY,rectRightX-rectLeftX,rectBottomY-rectTopY);

        for(int n = 1;n<1000;n++)
        {
           Color backgroundColour = getBackground();
           g.setColor(backgroundColour);
           g.fillOval(x,y,diameter,diameter);

           if(x<=rectLeftX)
              xChange = -xChange;
           if(x>=rectRightX)
              xChange = -xChange;

           if (y<=rectTopY);
             yChange = -yChange;
           if (y>=rectBottomY);
             yChange = -yChange;

             x = x+xChange;
             y = y+yChange;

             g.setColor(Color.blue);
             g.fillOval(x,y,diameter,diameter);
         }
      }

    }