Ball myBall = new Ball(1.25, "golfball");
Sphere mySphere = myBall;
mySphere.displayStatistics();

public double area() {
  double r = radius();
  return Math.PI * r * r;  // Math.PI is a constant
}  // end area



public class Sphere  {
  . . .  // everything as before
  public double area() {  // surface area
    return 4.0 * Math.PI * theRadius * theRadius;
  } // end area

  public void displayStatistics() {  
    System.out.println("\nRadius = " + radius()
               + "\nDiameter = " + diameter()
               + "\nCircumference = " + circumference()
               + "\nArea = " + area()
               + "\nVolume = " + volume());
  }  // end displayStatistics

  . . .
}  // end Sphere