C# 4 and .NET 4

4inheritance
WhaT ’ s in This ChaPTer
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Types of inheritance
Implementing inheritance
Access modifi ers
Interfaces
Chapter 3, “ Objects and Types, ” examined how to use individual classes in C#. The focus in that
chapter was how to defi ne methods, properties, constructors, and other members of a single
class (or a single struct). Although you learned that all classes are ultimately derived from the class
System.Object , you did not learn how to create a hierarchy of inherited classes. Inheritance is the
subject of this chapter. In this chapter, you see how C# and the .NET Framework handle inheritance.
TyPes of inheriTanCe
Let ’ s start 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:
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Implementation inheritance means that a type derives from a base type, taking all the base
type ’ s member fi elds and functions. With implementation inheritance, a derived type adopts
the base type ’ s implementation of each function, unless it is indicated in the defi nition 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 signifi cant amount of common functionality.
Interface inheritance means that a type inherits only the signatures of the functions and does
not inherit any implementations. This type of inheritance is most useful when you want to
specify that a type makes certain features available.
C# supports both implementation and interface inheritance. Both are baked into the framework
and the language from the ground up, thereby allowing you to decide which to use based on the
architecture of the application.
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