Class Hierarchy test

   

/*
Learning C# 
by Jesse Liberty

Publisher: O'Reilly 
ISBN: 0596003765
*/
 using System;

 class Window
 {
     // constructor takes two integers to
     // fix location on the console
     public Window(int top, int left)
     {
         this.top = top;
         this.left = left;
     }

     // simulates drawing the window
     public void DrawWindow()
     {
         Console.WriteLine("Drawing Window at {0}, {1}",
             top, left);
     }

     // these members are private and thus invisible
     // to derived class methods; we'll examine this
     // later in the chapter
     private int top;
     private int left;
 }

 // ListBox derives from Window
 class ListBox : Window
 {
     // constructor adds a parameter
     public ListBox(
         int top,
         int left,
         string theContents):
         base(top, left)  // call base constructor
     {
         mListBoxContents = theContents;
     }

     // a new version (note keyword) because in the
     // derived method we change the behavior
     public new void DrawWindow()
     {
         base.DrawWindow();  // invoke the base method
         Console.WriteLine ("Writing string to the listbox: {0}",
             mListBoxContents);
     }
     private string mListBoxContents;  // new member variable
 }

 public class HierarchyTester
 {
     public static void Main()
     {
         // create a base instance
         Window w = new Window(5,10);
         w.DrawWindow();

         // create a derived instance
         ListBox lb = new ListBox(20,30,"Hello world");
         lb.DrawWindow();
     }
 }