Chapter 4

Inheritance

Chapter 3, “Objects and Types,” examined how to use individual classes in C#. The focus in that chapter was how to define methods, constructors, properties, and other members of a single class (or a single struct). Although you did learn that all classes are ultimately derived from the class System.Object, you did not see how to create a hierarchy of inherited classes. Inheritance is the subject of this chapter. In this chapter, you will see how C# and the .NET Framework handle inheritance. Topics covered include:

  • Types of inheritance
  • Implementing inheritance
  • Access modifiers
  • Interfaces

Types of Inheritance

Let’s start off by reviewing exactly what C# does and does not support as far as inheritance is concerned.

Implementation versus Interface Inheritance

In object-oriented programming, there are two distinct types of inheritance — implementation inheritance and interface inheritance:

  • Implementation inheritance means that a type derives from a base type, taking all the base type’s member fields and functions. With implementation inheritance, a derived type adopts the base type’s implementation of each function, unless it is indicated in the definition of the derived type that a function implementation is to be overridden. This type of inheritance is most useful when you need to add functionality to an existing type, or when a number of related types share a significant amount of common functionality. A good example of this comes in the Windows Forms classes, ...

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