VB.Net/Class/Override

Overrides method from super(parent) class

<source lang="vbnet"> Imports System Public Class MainClass

   Shared Sub Main()
        Dim win As New Window(1, 2)
        Dim lb As New ListBox(3, 4, "Stand alone list box")
        Dim b As New Button(5, 6)
        win.DrawWindow(  )
        lb.DrawWindow(  )
        b.DrawWindow(  )
        Dim winArray(3) As Window
        winArray(0) = New Window(1, 2)
        winArray(1) = New ListBox(3, 4, "List box in array")
        winArray(2) = New Button(5, 6)
        Dim i As Integer
        For i = 0 To 2
            winArray(i).DrawWindow(  )
        Next i
   End Sub

End Class

Public Class Window
    Public Sub New(ByVal top As Integer, ByVal left As Integer)
        Me.top = top
        Me.left = left
    End Sub
    Public Overridable Sub DrawWindow(  )
        Console.WriteLine("Window: drawing Window at {0}, {1}", top, left)
    End Sub
    Protected top As Integer
    Protected left As Integer
End Class
Public Class ListBox
    Inherits Window
    Public Sub New(ByVal top As Integer, ByVal left As Integer, ByVal contents As String)
        MyBase.New(top, left)
        listBoxContents = contents
    End Sub
    Public Overrides Sub DrawWindow(  )
        MyBase.DrawWindow(  )
        Console.WriteLine("Writing string to the listbox: {0}", listBoxContents)
    End Sub
    Private listBoxContents As String " new member variable
End Class "ListBox
Public Class Button
    Inherits Window
    Public Sub New(ByVal top As Integer, ByVal 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 "DrawWindow
End Class "Button
          
      </source>

Override the Finalize Function

<source lang="vbnet"> Imports System Public Class MainClass

   Shared Sub Main(ByVal args As String())
     Dim circle1, circle2 As Circle
     circle1 = New Circle(72, 29, 4.5) " instantiate objects
     circle2 = New Circle(5, 5, 10)
     circle1 = Nothing " mark objects for garbage collection
     circle2 = Nothing
     System.GC.Collect() " request garbage collector to execute
   End Sub

End Class

Public Class Circle

  Inherits Point " Circle Inherits from class Point
  Private mRadius As Double
  " default constructor
  Public Sub New()
     " implicit call to Point constructor occurs here
     Radius = 0
     Console.WriteLine("Circle constructor: {0}", Me)
  End Sub " New
  " constructor
  Public Sub New(ByVal xValue As Integer, _
     ByVal yValue As Integer, ByVal radiusValue As Double)
     " use MyBase reference to Point constructor explicitly
     MyBase.New(xValue, yValue)
     Radius = radiusValue
     Console.WriteLine("Circle constructor: {0}", Me)
  End Sub " New
  " finalizer overrides version in class Point
  Protected Overrides Sub Finalize()
     Console.WriteLine("Circle Finalizer: {0}", Me)
     MyBase.Finalize() " call Point finalizer
  End Sub " Finalize
  " property Radius
  Public Property Radius() As Double
     Get
        Return mRadius
     End Get
     Set(ByVal radiusValue As Double)
        If radiusValue > 0 Then
           mRadius = radiusValue
        End If
     End Set
  End Property " Radius
  " calculate Circle diameter
  Public Function Diameter() As Double
     Return mRadius * 2
  End Function " Diameter
  " calculate Circle circumference
  Public Function Circumference() As Double
     Return Math.PI * Diameter()
  End Function " Circumference
  " calculate Circle area
  Public Overridable Function Area() As Double
     Return Math.PI * mRadius ^ 2
  End Function " Area
  " return String representation of Circle
  Public Overrides Function ToString() As String
     " use MyBase reference to return Point String
     Return "Center = " & MyBase.ToString() & _
        "; Radius = " & mRadius
  End Function " ToString

End Class Public Class Point

  " point coordinate
  Private mX, mY As Integer
  " default constructor
  Public Sub New()
     " implicit call to Object constructor occurs here
     X = 0
     Y = 0
     Console.WriteLine("Point constructor: {0}", Me)
  End Sub " New
  " constructor
  Public Sub New(ByVal xValue As Integer, _
     ByVal yValue As Integer)
     " implicit call to Object constructor occurs here
     X = xValue
     Y = yValue
     Console.WriteLine("Point constructor: {0}", Me)
  End Sub " New
  " finalizer overrides version in class Object
  Protected Overrides Sub Finalize()
     Console.WriteLine("Point Finalizer: {0}", Me)
     MyBase.Finalize() " call Object finalizer
  End Sub " Finalize
  " property X
  Public Property X() As Integer
     Get
        Return mX
     End Get
     Set(ByVal xValue As Integer)
        mX = xValue " no need for validation
     End Set
  End Property " X
  " property Y 
  Public Property Y() As Integer
     Get
        Return mY
     End Get
     Set(ByVal yValue As Integer)
        mY = yValue " no need for validation
     End Set
  End Property " Y
  " return String representation of Point
  Public Overrides Function ToString() As String
     Return "[" & mX & ", " & mY & "]"
  End Function " ToString

End Class

      </source>