// RandomBall.java

          public class RandomBall extends Ball

          {

          public RandomBall (int newX, int newY, int newRadius, int newXMotion, int newYMotion)

          {

          // call the Ball constructor

          super( newX, newY, newRadius, newXMotion, newYMotion );

          }

          public void move()

          {

          // 50% chance of chaning X motion

          if( Math.random() > 0.5 )

          dx = -dx;

          // 50% chance of changing Y motion

          if( Math.random() > 0.5 )

          dy = -dy;

          // move centre of object

          x = x + dx;

          y = y + dy;

          }

          } // class RandomBall