VB.Net/Class/Abstract Class

Abstract (MustInherit) Class

Imports System
Public Class MainClass
    
    Shared Sub Main()
       Dim winArray(3) As Window
       winArray(0) = New ListBox(1, 2, "First List Box")
       winArray(1) = New ListBox(3, 4, "Second List Box")
       winArray(2) = New Button(5, 6)
       Dim i As Integer
       For i = 0 To 2
          winArray(i).DrawWindow(  )
       Next i
    End Sub
End Class

 MustInherit Public Class Window
    Public Sub New(top As Integer, left As Integer)
       Me.top = top
       Me.left = left
    End Sub "New
    Public MustOverride Sub DrawWindow(  )
    Protected top As Integer
    Protected left As Integer
 End Class "Window
 Public Class ListBox
    Inherits Window
    Public Sub New(top As Integer, left As Integer, contents As String)
       MyBase.New(top, left) " call base constructor
       listBoxContents = contents
    End Sub "New

    Public Overrides Sub DrawWindow(  )
       Console.WriteLine("Writing string to the listbox: {0}", listBoxContents)
    End Sub "DrawWindow
    Private listBoxContents As String 
 End Class 
 Public Class Button
    Inherits Window
    Public Sub New(top As Integer, left As Integer)
       MyBase.New(top, left)
    End Sub 
    Public Overrides Sub DrawWindow(  )
       Console.WriteLine("Drawing a button at {0}, {1}" + ControlChars.Lf, top, left)
    End Sub
 End Class

Define Abstract Class and Reference Class by it

Imports System
Public Class MainClass
  Shared Sub Main()
    Dim tom As New Employee("Tom", 50000, "111-11-1234")
    Dim sally As New Employee("Sally", 150000, "111-11-2234")
    Dim ourEmployees(1) As PayableEntity
    ourEmployees(0) = tom
    ourEmployees(1) = sally
    Dim anEmployee As PayableEntity
    For Each anEmployee In ourEmployees
      Console.WriteLine(anEmployee.TheName & " has tax id " & anEmployee.TaxID )
    Next
  End Sub
End Class
Public MustInherit Class PayableEntity
  Private m_Name As String
  Public Sub New(ByVal itsName As String)
    m_Name = itsName
  End Sub
  ReadOnly Property TheName() As String
    Get
      Return m_Name
    End Get
  End Property
  Public MustOverride Property TaxID() As String
End Class
Public Class Employee
  Inherits PayableEntity
  Private m_Salary As Decimal
  Private m_TaxID As String
  Private Const LIMIT As Decimal = 0.1D
  Public Sub New(ByVal theName As String, ByVal curSalary As Decimal, ByVal TaxID As String)
    MyBase.New(theName)
    m_Salary = curSalary
    m_TaxID = TaxID
  End Sub
  Public Overrides Property TaxID() As String
    Get
      Return m_TaxID
    End Get
    Set(ByVal Value As String)
        m_TaxID = Value
    End Set
  End Property
  ReadOnly Property Salary() As Decimal
    Get
      Return MyClass.m_Salary
    End Get
  End Property
  Public Overridable Overloads Sub RaiseSalary(ByVal Percent As Decimal)
    If Percent > LIMIT Then
      "not allowed
      Console.WriteLine("Percent > LIMIT")
    Else
      m_Salary = (1D + Percent) * m_Salary
    End If
  End Sub
  Public Overridable Overloads Sub RaiseSalary(ByVal Percent As _
  Decimal, ByVal Password As String)
    If Password = "special" Then
      m_Salary = (1D + Percent) * m_Salary
    End If
  End Sub
End Class