In C#, the specialization relationship is implemented using a principle called 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.
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). These members can be treated just as if they were created in the derived class.
The derived class is free to implement its own version of a base
class method. This is called
hiding the base class method and is accomplished
by marking the method with the keyword
This is a different use of the keyword
you’ve seen earlier in this book. In Chapter 8,
new was used to create an
object on the heap; here
new is used to replace
the base class method. Programmers say the keyword
new is overloaded, which means that the word has more than one meaning ...