import java.awt.*;
//to be more specific, java.awt.Point does the job

public class CannonBall extends Ball {

   public CannonBall (Point loc, int r, double dx, double dy) {
      super(loc, r); //invoke Ball's constructor
      setMotion(dx, dy);
   }

   public static final double GravityEffect = 0.3;

   public void move () {
      changeInY += GravityEffect; //short for changeInY = changeInY + GravityEffect;
      super.move(); //update the ball position
   }
}