VB.Net/Class/Override

Overrides method from super(parent) class

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

Override the Finalize Function

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