Lesson 16 - Abstract class, comparing and operator overloading in VB.NET
In the previous lesson, Type casting and object hierarchy in VB.NET, we learned about type casting and created an object hierarchy with a common ancestor in Visual Basic .NET. In today's tutorial, we're going to continue with that project.
Abstract class
An abstract class is a class whose instance does not make sense. Mainly because it is too vague, e.g. our Animal class. The point is to call on specific Animal descendants, e.g. a dog, so we won't actually instantiate the Animal class directly ever. In other words, it's better to prevent any instantiation of the class overall. To do that, we simply add the "MustInherit" modifier before the Animal class:
Public MustInherit Class Animal . . .
The program works the same as before, but if we try to create an instance of the Animal class, we'll get an error:
' this code won't work animals.Add(New Animal())
Other than preventing instantiation, abstract classes can do several other things
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This tutorial explains abstract classes in Visual Basic. We'll learn about interfaces, implement custom comparing with IComparable, and overload operators.
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