What are abstract classes?
The features of the abstract class are as follows:-
1. You can not create an object of the abstract class.
2. The Abstract class is designed to act as a base class (to be inherited by another classes). In the program development the Abstract class is a design concept and provides a base upon which other classes are built.
3. The Abstract classes are similar to the interfaces. After declaring an abstract class, it can't be instantiated on its own, it must be inherited.
4. In VB.NET abstract classes are created by using the "MustInherit" keyword.In the C# we have "Abstract" keyword.
5. The Abstract classes can have implementation or pure abstract methods which must be implemented in the child class.
Public MustInherit Class ClsAbstract
' use the mustinherit class to declare the class as abstract
Public Function Add(ByVal intnum1 As Integer, ByVal intnum2 As
Integer) As Integer
Return intnum1 + intnum2
End Function
' left this seconf function to be completed by the inheriting class
Public MustOverride Function MultiplyNumber(ByVal intnum1 As
Integer, ByVal intnum2 As Integer) As Integer
End Class
Public Class ClsChild
Inherits ClsAbstract
' class child overrides the Multiplynumber function
Public Overrides Function MultiplyNumber(ByVal intnum1 As
Integer, ByVal intnum2 As Integer) As Integer
Return intnum1 * intnum2
End Function
End Class
