VB.Net Tutorial/Class Module/MustInherit

Inherited MustInherit

Public MustInherit Class Cls1
    Public MustOverride Function greet1() As String
End Class
Public MustInherit Class Cls2
    Inherits Cls1
    Public MustOverride Function greet2() As String
End Class
Public Class Cls3
    Inherits Cls2
    Public Overrides Function greet1() As String
    End Function
    Public Overrides Function greet2() As String
    End Function
End Class

MustInherit class

Option Strict On
 Imports System
 
 MustInherit Public Class Control
    Public Sub New(top As Integer, left As Integer)
       Me.top = top
       Me.left = left
    End Sub
    Public MustOverride Sub DrawControl( )
    Protected top As Integer
    Protected left As Integer
 End Class 
 Public Class Label
    Inherits Control
    Public Sub New(top As Integer, left As Integer, contents As String)
       MyBase.New(top, left) 
       listBoxContents = contents
    End Sub
    Public Overrides Sub DrawControl( )
       Console.WriteLine("Writing string to the listbox: {0}", listBoxContents)
    End Sub 
    Private listBoxContents As String 
 End Class
 Public Class Button
    Inherits Control
    Public Sub New(top As Integer, left As Integer)
       MyBase.New(top, left)
    End Sub
    Public Overrides Sub DrawControl( )
       Console.WriteLine("Drawing a button at {0}, {1}" + ControlChars.Lf, top, left)
    End Sub 
 End Class
 Public Class Tester
    Shared Sub Main( )
       Dim winArray(3) As Control
       winArray(0) = New Label(1, 2, "A")
       winArray(1) = New Label(3, 4, "B")
       winArray(2) = New Button(5, 6)
       Dim i As Integer
       For i = 0 To 2
          winArray(i).DrawControl( )
       Next i
    End Sub "Main
 End Class "Tester

Writing string to the listbox: A
Writing string to the listbox: B
Drawing a button at 5, 6

Polymorphic

Imports System.Collections
public class MustOverrideMustInherit
   public Shared Sub Main
        Dim ShapeArray As New ArrayList()
        ShapeArray.Add(New Cone())
        ShapeArray.Add(New Cube())
        ShapeArray.Add(New Cylinder())
        ShapeArray.Add(New Rectangle())
        Dim shape As Shape
        For Each shape In ShapeArray
            Console.WriteLine(shape.DrawMe())
        Next
   End Sub
End class
Public MustInherit Class Shape
    Public MustOverride Function DrawMe() As String
End Class
Public Class Cone
    Inherits Shape
    Public Overrides Function DrawMe() As String
        Return "Drawing Cone..."
    End Function
End Class
Public Class Rectangle
    Inherits Shape
    Public Overrides Function DrawMe() As String
        Return "Drawing Rectangle..."
    End Function
End Class
Public Class Oval
    Inherits Shape
    Public Overrides Function DrawMe() As String
        Return "Drawing Oval..."
    End Function
End Class
Public Class Cylinder
    Inherits Shape
    Public Overrides Function DrawMe() As String
        Return "Drawing Cylinder..."
    End Function
End Class
Public Class Cube
    Inherits Shape
    Public Overrides Function DrawMe() As String
        Return "Drawing Cube..."
    End Function
End Class

Drawing Cone...
Drawing Cube...
Drawing Cylinder...
Drawing Rectangle...

Use MustInherit to define abstract class

Public MustInherit Class Printable
    Public PageData As String
    Public MustOverride Sub ShowPage()
    Public Sub New(ByVal Message As String)
        PageData = Message
    End Sub
End Class
Public Class Word
    Inherits Printable
    Public Overrides Sub ShowPage()
        Console.WriteLine("word: " & PageData)
    End Sub
    Public Sub New(ByVal Message As String)
        MyBase.New(Message)
    End Sub
End Class
Public Class Text
    Inherits Printable
    Public Overrides Sub ShowPage()
        Console.WriteLine("Test: " & PageData)
    End Sub
    Public Sub New(ByVal Message As String)
        MyBase.New(Message)
    End Sub
End Class

Module Module1

    Sub Main()
        Dim WebPage As Word = New Word("word page")
        Dim MobilePage As Text = New Text("text file")
        WebPage.ShowPage()
        Console.WriteLine()
        MobilePage.ShowPage()
    End Sub
End Module

word: word page
Test: text file