Abstract class: - It is an incomplete class whose object cannot be created. It contains the skeleton of the method, which is implemented by derived class. The abstract class is prefixed by the keyword MustInherit. The methods with in the class are prefixed by MustOverride keyword. The derived class procedure, which implements the abstract class, is prefixed by Overrides keyword.

Program

Public Class Form1

Private Sub Button1_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Button1.Click

Dim a As New raj1

a.ravi("Rahul")

End Sub

Public MustInherit Class raj

Public MustOverride Sub ravi(ByVal s As String)

End Class

Public Class raj1

Inherits raj

Public Overrides Sub ravi(ByVal s As String)

MsgBox("Hello:" & s)

End Sub

End Class

Interface: - It is a specification of class members not the implementation of members.

It is the substitute of multiple inheritance more than one interface can be implemented by a single class. The members with in the interface are not defined. It is public by default. Variables cannot be declared within the interface. Both sub procedure and function procedure can be stored in the interface.

Program

Public Class Form2

Private Sub Button1_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Button1.Click

Dim a As New raj1

a.sagar(25)

a.amit("Abhijeet")

MsgBox(a.rahul(10, 20))

End Sub

Public Interface raj

Sub sagar(ByVal x As Integer)

Sub amit(ByVal s As String)

Function rahul(ByVal x As Integer, ByVal y As Integer)

End Interface

Public Class raj1

Implements raj

Public Sub amit(ByVal s As String) Implements raj.amit

MsgBox("Hello:" & s)

End Sub

Public Function rahul(ByVal x As Integer, ByVal y As Integer) As Object Implements raj.rahul

Dim z As Integer

z = x + y

Return z

End Function

Public Sub sagar(ByVal x As Integer) Implements raj.sagar

MsgBox(x)

End Sub

End Class

Thanks for reading