Interfaces in VB .NET

OOP with VB

Interfaces

Interfaces allow us to create definitions for component interaction. They also provide another way of implementing polymorphism. Through interfaces, we specify methods that a component must implement without actually specifying how the method is implemented. We just specify the methods in an interface and leave it to the class to implement those methods. Visual Basic .NET does not support multiple inheritance directly but using interfaces we can achieve multiple inheritance. We use the Interface keyword to create an interface and implements keyword to implement the interface. Once you create an interface you need to implement all the methods specified in that interface. The following code demonstrates the use of interface.

Imports System.Console
Module Module1

Sub Main()
Dim OneObj As New One()
Dim TwoObj As New Two()
'creating objects of class One and Two
OneObj.disp()
OneObj.multiply()
TwoObj.disp()
TwoObj.multiply()
'accessing the methods from classes as specified in the interface
End Sub

End Module

Public Interface Test
'creating an Interface named Test
Sub disp()
Function Multiply() As Double
'specifying two methods in an interface
End Interface

Public Class One
Implements Test
'implementing interface in class One

Public i As Double = 12
Public j As Double = 12.17

Sub disp() Implements Test.disp
'implementing the method specified in interface
WriteLine("sum of i+j is" & i + j)
Read()
End Sub

Public Function multiply() As Double Implements Test.Multiply
'implementing the method specified in interface
WriteLine(i * j)
Read()
End Function

End Class

Public Class Two
Implements Test
'implementing the interface in class Two

Public a As Double = 20
Public b As Double = 32.17

Sub disp() Implements Test.disp
WriteLine("Welcome to Interfaces")
Read()
End Sub

Public Function multiply() As Double Implements Test.Multiply
WriteLine(a * b)
Read()
End Function

End Class

Output of above code is the image below.