Polymorphism: Object Oriented Programming ( visual basic )

Computer Science(9608) notes and Resources

Polymorphism is an object-oriented programming concept that refers to the ability of a variable, function or object to take on multiple forms. A language that features polymorphism allows developers to program in the general rather than program in the specific. There are two types of polymprphism. They are:

i.  Compile time polymorphism

ii. Run time Polymorphism

Compile time polymorphism:- compile time polymorphism achieved by "Method Overloading", means that same name function with different  parameters in same class called compile time polymorphism.

Example 1

Module Module1

    Public Class One

        Public i, j, k As Integer

        Public Function add(ByVal i As Integer) As Integer

            'function with one argument

            Return i

        End Function

        Public Function add(ByVal i As Integer, ByVal j As Integer) As Integer

            'function with two arguments

            Return i + j

        End Function

        Public Function add(ByVal i As Integer, ByVal j As Integer, ByVal k As Integer) As Integer

            'function with three arguments

            Return i + j + k

        End Function

    End Class

    Sub Main()

        Dim objone As New One()

        Console.WriteLine(objone.add(10))

        'calls the function with one argument

        Console.WriteLine(objone.add(10, 20))

        'calls the function with two arguments

        Console.WriteLine(objone.add(10, 20, 30))

        'calls the function with three arguments

        Console.ReadLine()

    End Sub

End Module

Example 2

Module Module1

    Public Class Polymorphism

        Public A, B, C As Integer

        Public Function Sum(ByVal A As Integer) As Integer

            'function with one argument

            Return A

        End Function

        Public Function Sum(ByVal A As Integer, ByVal B As Integer) As Integer

            'function with two arguments

            Return A + B

        End Function

        Public Function Sum(ByVal A As Integer, ByVal B As Integer, ByVal C As Integer) As Integer

            'function with three arguments

            Return A + B + C

        End Function

    End Class

    Sub Main()

        Dim Objpolymorphism As New Polymorphism()

        Console.WriteLine(Objpolymorphism.Sum(20))

        'calls the function with one argument

        Console.WriteLine(Objpolymorphism.Sum(20, 40))

        'calls the function with two arguments

        Console.WriteLine(Objpolymorphism.Sum(20, 40, 60))

        'calls the function with three arguments

        Console.ReadLine()

    End Sub

End Module

Example 3

Module Module1

    Class test

        Dim r As Double

        Public Sub area(ByVal r As Double)

            Console.Write("Area of the Circle :")

            Console.WriteLine(1 / 3 * 3.14 * r * r * r)

        End Sub

        Dim length As Integer

        Dim width As Integer

        Public Sub area(ByVal length As Integer, ByVal width As Integer)

            Console.Write(" Area of the Rectangle :")

            Console.WriteLine(length * width)

        End Sub

    End Class

    Sub Main()

        Dim objtest As New test()

        objtest.area(3)

        objtest.area(4, 5)

        Console.ReadLine()

    End Sub

End Module

Run time Polymorphism:- Run time polymorphism achieved by "Method Overriding or Operator Overloading", means that same name function with same parameters in different different classes called Run time Polymorphism.

Overriding : Overriding in VB.net is method by which a inherited property or a method is overidden to perform a different functionality in a derived class. The base class function is declared using a keyword Overridable and the derived class function where the functionality is changed contains an keyword Overrides.

Example 1

Module Module1

    Class over

        Public Overridable Function add(ByVal x As Integer, ByVal y As Integer)

            Console.WriteLine("Function Inside Base Class")

            Return (x + y)

        End Function

    End Class

    Class over2 : Inherits over

        Public Overrides Function add(ByVal x As Integer, ByVal y As Integer)

            Console.WriteLine(MyBase.add(120, 100))

            Console.WriteLine("Function Inside Derived Class")

            Return (x + y)

        End Function

    End Class

    Sub Main()

        Dim objover2 As New over2

        Console.WriteLine(objover2.add(10, 100))

        Console.ReadLine()

    End Sub

End Module

Description:  In the above overriding example the base class function add is overridden in the derived class using the MyBase.add(120,100) statement. So first the overidden value is displayed, then the value from the derived class is displayed.

Example 2

Module Module1

    Public Class test

        Public Overridable Function show()

            Console.WriteLine("my country")

        End Function

    End Class

    Public Class test2 : Inherits test

        Public Overrides Function show()

            Console.WriteLine(MyBase.show())

            Console.WriteLine("nepal")

        End Function

    End Class

    Sub Main()

        Dim objtest2 As test2 = New test2()

        objtest2.show()

        Console.ReadLine()

    End Sub

End Module

                                                           - CIE A-LEVEL COMPUTER SCIENCE (  9608 )