Inheritance

Inheritance is one of the most important features of the .NET Framework. A class can inherit or derive from another class, meaning that the new class can have all properties, methods, and members exposed by the first class, which is called base class, and can then define its own members. Inherited members can then be overridden to adapt their behavior to the new class’ context. The .NET Framework provides one-level inheritance, meaning that a class can inherit from one other class per time. Each class derives implicitly from System.Object. The Inherits keyword is used to inherit classes. The following code provides an example of a base class named Person and of a derived class named Customer:

In the preceding example the Person class overrides (that is, provides a new definition of) the System.Object.ToString method. The Customer class exposes a new CompanyName property whereas, via inheritance, it exposes the FirstName and LastName properties. Finally, the class also overrides the Person.ToString method. Inheritance is discussed in Chapter 12. “Inheritance.”