Rectangle.java w/o special methods

public class Rectangle{//class header
   //data - instance variables
   private double length, width;

   //functionality - methods
   public void setLength( double len ){
      length = len;
   }

   public void setWidth( double wid ){
      width = wid;
   }

   public double area(){
      return length * width;
   }

   public double perimeter(){
      return 2 * length + 2 * width;
   }

   public double diagonal(){
      return Math.sqrt( Math.pow(width,2) + Math.pow(length,2) );
   }
}