Create shape class as abstract class having area function.Create rectangle, triangle, square class based on this class in VB.NET.

Here this program we use MustInherit Class, MustOverride Function and how to create class, create object of class and import statement in VB.NET.

Shape.vb

Public MustInherit Class Shape
Public MustOverride Function Area(ByVal a As Integer, ByVal b As Integer) As Integer
End Class

square.vb

Public Class square
    Inherits Shape
    Public Overrides Function Area(ByVal a As Integer, ByVal b As Integer) As Integer
        Return a * b
    End Function
End Class

rectangle.vb

Public Class rectangle
    Inherits Shape
    Public Overrides Function Area(ByVal a As Integer, ByVal b As Integer) As Integer
        Return a * b
    End Function
End Class

triangle.vb

Public Class triangle
    Inherits Shape
    Public Overrides Function Area(ByVal a As Integer, ByVal b As Integer) As Integer
        Return (a * b) / 2
    End Function
End Class

Form1.vb

Imports area_of_shape.square
Imports area_of_shape.rectangle
Imports area_of_shape.triangle
Public Class Form1
    Dim S As New square
    Dim R As New rectangle
    Dim T As New triangle
    Private Sub Button1_Click(sender As Object, e As EventArgs) Handles Button1.Click
        If RadioButton1.Checked Then
            Label3.Text = "Area of Square is :" & S.Area(Val(TextBox1.Text), Val(TextBox1.Text))
        ElseIf RadioButton2.Checked Then
            Label3.Text = "Area of Rectangle is :" & R.Area(Val(TextBox1.Text), Val(TextBox2.Text))
        ElseIf RadioButton3.Checked Then
            Label3.Text = "Area of Triangle is :" & T.Area(Val(TextBox1.Text), Val(TextBox2.Text))
        End If
    End Sub
    Private Sub RadioButton1_CheckedChanged(sender As Object, e As EventArgs) Handles RadioButton1.CheckedChanged, RadioButton2.CheckedChanged, RadioButton3.CheckedChanged
        If RadioButton1.Checked Then
            Label1.Text = "Side"
            TextBox1.Visible = True
            TextBox2.Visible = False
            Label2.Text = ""
        ElseIf RadioButton2.Checked Then
            Label1.Text = "Length"
            TextBox1.Visible = True
            Label2.Text = "Width"
            TextBox2.Visible = True
        Else
            Label1.Text = "Base"
            TextBox1.Visible = True
            Label2.Text = "Height"
            TextBox2.Visible = True
        End If
        TextBox1.Clear()
        TextBox2.Clear()
        Label3.Text = "Enter Number in Box"
    End Sub
End Class

DESIGNING: