Programming C#, Second Edition

Inheritance

In C#, the specialization relationship is typically implemented using inheritance. This is not the only way to implement specialization, but it is the most common and most natural way to implement this relationship.

Saying that ListBox inherits from (or derives from) Window indicates that it specializes Window. Window is referred to as the base class, and ListBox is referred to as the derived class. That is, ListBox derives its characteristics and behaviors from Window and then specializes to its own particular needs.

Implementing Inheritance

In C#, you create a derived class by adding a colon after the name of the derived class, followed by the name of the base class:

public class ListBox : Window

This code declares a new class, ListBox, that derives from Window. You can read the colon as “derives from.”

The derived class inherits all the members of the base class, both member variables and methods. The derived class is free to implement its own version of a base class method. It does so by marking the new method with the keyword new. (The new keyword is also discussed in Section 5.3.3, later in this chapter.) This indicates that the derived class has intentionally hidden and replaced the base class method, as used in Example 5-1.

Example 5-1. Using a derived class

using System; public 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 ...