C#初始化基类

using System;

namespace RectangleApplication {

   class Rectangle {
      //member variables
      protected double length;
      protected double wIDth;

      public Rectangle(double l, double w) {
         length = l;
         wIDth = w;
      }

      public double GetArea() {
         return length * wIDth;
      }

      public voID display() {
         Console.Writeline("Length: {0}", length);
         Console.Writeline("WIDth: {0}", wIDth);
         Console.Writeline("Area: {0}", GetArea());
      }
   }//end class Rectangle  

   class tabletop : Rectangle {
      private double cost;
      public tabletop(double l, double w) : base(l, w) { }

      public double GetCost() {
         double cost;
         cost = GetArea() * 70;
         return cost;
      }

      public voID display() {
         base.display();
         Console.Writeline("Cost: {0}", GetCost());
      }
   }

   class ExecuteRectangle {

      static voID Main(string[] args) {
         tabletop t = new tabletop(4.5, 7.5);
         t.display();
         Console.Readline();
      }
   }
}