C# 2008 Programmer's Reference

Chapter 5. Interfaces

When defining a class, you have to provide the implementation for all its methods and properties. However, there are times when you do not want to provide the actual implementation of how a class might work. Rather, you want to describe the functionalities of the class. This set of descriptions is like a contract, dictating what the class will do, the types of parameters needed, and the type of return results. In object-oriented programming, this contract is known as an interface.

An interface defines a class and its members without providing any implementation. When using interfaces in programming, generally three parties are involved:

• Interface definition — The interface defines the composition of a class, such as methods, properties, and so on. However, the interface does not provide any implementation for any of these members.

• Implementing class — The class that implements a particular interface provides the implementation for all the members defined in that interface.

• Clients — Objects that instantiate from the implementing classes are known as the client. The client invokes the methods defined in the interface, whose implementation is provided by the implementing class.

Differences between an Interface and an Abstract Base Class

Conceptually, an abstract class is similar to an interface; however, they do have some subtle differences:

• An abstract class can contain a mixture of concrete methods (implemented) and abstract methods (an abstract class needs at least ...