Programming Visual Basic .NET, Second Edition

Chapter 5. Classes and Objects

Chapter 3 discusses the primitive types built into the VB.NET language, such as Integer, Long, and Single. The true power of VB.NET, however, lies in its capacity to let the programmer define new types to suit particular problems. It is this ability to create new types that characterizes an object-oriented language. You specify new types in VB.NET by declaring and defining classes.

Particular instances of a class are called objects. The difference between a class and an object is the same as the difference between the concept of a Dog and the particular dog who is shedding on your carpet as you read this. You can’t play fetch with the definition of a Dog, only with an instance.

A Dog class describes what dogs are like: they have weight, height, eye color, hair color, disposition, and so forth. They also have actions they can perform, such as eat, walk, bark, and sleep. A particular dog (such as my dog Milo) will have a specific weight (62 pounds), height (22 inches), eye color (black), hair color (yellow), disposition (angelic), and so forth. He is capable of all the actions—methods, in programming parlance—of any dog (though if you knew him you might imagine that eating is the only method he implements).

The huge advantage of classes in object-oriented programming is that classes encapsulate the characteristics and capabilities of a type in a single, self-contained unit. Suppose, for instance, you want to sort the contents of a Windows listbox ...