Summary

Classes are programming abstractions that group data and related behavior in nicely encapsulated packages. After you define a class, you can instantiate it to create an instance of the class. You can interact with the new object by using its properties, methods, and events.

Inheritance enables you to derive one class from another. You can then add, remove, or modify the behavior that the child class inherits from the parent class. Sometimes it makes sense to think of the classes in inheritance hierarchies in a top-down manner, so child classes refine the features of their parents. At other times, it makes sense to use a bottom-up view and think of a parent class as abstracting the features of its children.

Interface inheritance lets you define some of the features of a class without using true class inheritance. This gives you another method for using polymorphism and lets you build classes that, in a sense, appear to inherit from multiple parents.

Polymorphism enables you to treat an object as if it were of an ancestor’s type. For example, if the Manager class inherits from Employee and Employee inherits from Person, then you can treat a Manager object as if it is a Manager, Employee, or Person.

In addition to these features, Visual Basic .NET enables you to overload a class’s subroutines, functions, and operators. It lets you create different methods with the same name but different parameters. The compiler selects the right version of the method based on the parameters you pass to it.

These object-oriented concepts provide the general background you need to understand classes in Visual Basic. Chapter 16 describes the specifics of classes and structures in Visual Basic .NET. It shows how to declare and instantiate classes and structures and explains the differences between the two.