public class Methods3 {
  public static void main(String[] args) {
    Rectangle[] data = { new Rectangle(), new Square()};
    data[0].setSides(2,3);
    data[1].setSides(2,2);
    for (int i=0; i < data.length; i++)
      System.out.println(data[i].getArea()); 
  }
}

class Rectangle {
  protected double width;
  protected double height;
  public double getArea() { return width*height; }
  public void setSides(double w, double h) { 
    width = w; 
    height = h; 
  }
}
class Square extends Rectangle { 
  public void setSides(double s1, double s2) { 
    if (s1!=s2)  { 
      System.out.println("not a square!");
      System.exit(0);
    }
    super.setSides(s1, s1);
  }
}