We know that all the classes can
be separated in to two categories, concrete classes and abstract
classes
Concrete classes:-"Classes are concrete classes if
they support object instantiations using the new operator."
Abstract classes:-"Classes are abstract classes if
they do not support object instantiations."
Now we will discuss about the Abstract classes in VB.NET, explaining why we use
the abstract classes in programming.because an abstract base class enable you to define a programming contract with
the partially completed implementation and other functionality that are given bellow
- Defining a class as an abstract class enables you to document your intention to use the class exclusively as base class.
- An abstract base class is like a concrete base class in that it may contain both override and non override methods.
- Abstract base classes are more flexible than concrete base classes because they can also contain abstract members.
Syntax of abstract classes in VB.NET:-
When you create the definition for the base class, you must add the
MustInherit keyword to make it abstract
Public MustInherit Class
className
Public Overridable Function functionName()
As String
Return " That are vehicle"
End Function
'othere class member function omity for
clarity
End Class
Note:-A class
defined with the MustInherit keyword is abstract and , therefore ,can not be
directly used to create an object.
coding for abstract classes in VB.NET:
Module
Module1
Public
MustInherit Class AbstractClass
'declaring an abstract class with
MustInherit keyword
Public MustOverride Function
Add() As Integer
Public MustOverride Function
Subs() As Integer
'declaring two abstract members
with MustOverride keyword
End
Class
Public Class
AbstractOne
: Inherits AbstractClass
'implementing the abstract class by
inheriting
Dim i
As Integer = 50
Dim j As Integer = 30
'declaring two integers
Public
Overrides Function Add()
As Integer
Return i + j
End
Function
'implementing the add method
Public
Overrides Function Subs()
As Integer
Return i - j
End
Function
'implementing the subs method
End Class
Public
Class Abstracttwo : Inherits
AbstractClass
Dim X As Integer = 34
Dim y As Integer = 30
Public
Overrides Function Add()
As Integer
Return X + y
End
Function
Public
Overrides Function Subs()
As Integer
Return X - y
End
Function
End
Class
Sub Main()
Dim abs
As New AbstractOne()
'creating an instance of AbstractOne
Console.WriteLine("first class
Sum is" & " " & abs.Add())
Console.WriteLine("first Substraction
is " & " " & abs.Subs())
Dim abt
As New Abstracttwo()
'creating an instance of AbstractOne
Console.WriteLine("second class
Sum is" & " " & abt.Add())
Console.WriteLine("second class
Substraction is " & " " & abt.Subs())
'displaying output
End
Sub
End Module
Output:
