C# 24-Hour Trainer, 2nd Edition

Lesson 27

Using Interfaces

In .NET programming, an interface is like a contract. It defines the public properties, methods, and events that a class must provide to satisfy the contract. It doesn't indicate how the class must provide these features, however. That's left up to the class's code. It only defines an interface that the class must show to the rest of the world.

In this lesson, you learn how to implement interfaces that are predefined by the .NET Framework. You also learn how to define your own interfaces to make your code safer and more efficient.

Interface Advantages

The following sections discuss two of the most important advantages provided by interfaces: multiple inheritance and code generalization.

Multiple Inheritance

Suppose you define a Vehicle class with properties such as NumberOfPassengers, MilesPerGallon, and NumberOfCupHolders. From this class you can derive other classes such as Car, PickupTruck, and Unicycle.

Suppose you also define a Domicile class that has properties such as SquareFeet, NumberOfBedrooms, and HasAnnoyingNeighbor. From this class you can derive Apartment, Condo, and VacationHome.

Next you might like to derive the MotorHome class from both Vehicle and Domicile so it has the properties and methods of both parent classes. Unfortunately you can't do that in C#. In C#, a class can inherit from only a single parent class.

Although a class can have only one parent, it can implement any number of interfaces. For example, if you turn the ...