Section 3.7. Specialization

3.7 Specialization

The second pillar , specialization, is implemented in C# by declaring that a new class derives from an existing class. When you do so, the specialized class inherits the characteristics of the more general class. The specialized class is called a derived class, while the more general class is known as a base class.

The specialization relationship is referred to as the is-a relationship. A dog is a mammal, a car is a vehicle. (Dog would be derived from the base class Mammal and Car from the base class Vehicle.)

Specialization allows you to create a family of objects. In Windows a button is a control. A list box is a control. Controls have certain characteristics ( color , size , location) and certain abilities (can be drawn, can be selected). These characteristics and abilities are inherited by all of their derived types, which allows for a very powerful form of reuse. Rather than cutting and pasting code from one type to another, the derived type inherits the shared fields and methods . If you change how a shared ability is implemented, you do not have to update code in every derived type; they inherit the changes.

For example, a Manager is a special type of Employee. The Manager adds new capabilities (hiring, firing, rewarding , praising) and a new state (annual objectives, management level, etc.). The Manager, however, also inherits the characteristics and capabilities common to all Employees. Thus a Manager has an address, a name , and an employee ID, and Managers can be given raises, can be laid off, and so forth. You'll see specialization at work in Chapter 11.