Inheritance and polymorphism : Polymorphism « Class Module « VB.Net Tutorial

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VB.Net Tutorial » Class Module » Polymorphism 
6.15.2.Inheritance and polymorphism
Class Tester

   
   Shared Sub Main()
      Dim point1, point2 As Point
      Dim circle1, circle2 As Circle

      point1 = New Point(3050)
      circle1 = New Circle(120892.7)

      Console.WriteLine("Point point1: " & point1.ToString() & _
         vbCrLf & "Circle circle1: " & circle1.ToString())

      point2 = circle1

      Console.WriteLine("Circle circle1 (via point2): " & point2.ToString())

      circle2 = CType(point2, Circle' allowed only via cast

      Console.WriteLine("Circle circle1 (via circle2): " & circle2.ToString())

      If (TypeOf point1 Is CircleThen
         circle2 = CType(point1, Circle)
         Console.WriteLine("cast successful")
      Else
         Console.WriteLine("point1 does not refer to a Circle")
      End If
   End Sub

End Class 

Public Class Point
   Private mX, mY As Integer

   Public Sub New()
   End Sub ' New

   Public Sub New(ByVal xValue As Integer, _
      ByVal yValue As Integer)
   End Sub ' New
   Public Overrides Function ToString() As String
      Return "[" & mX & ", " & mY & "]"
   End Function ' ToString

End Class

Public Class Circle
   Inherits Point 

   Private mRadius As Double

   Public Sub New()
   End Sub ' New

   Public Sub New(ByVal xValue As Integer, _
      ByVal yValue As Integer, ByVal radiusValue As Double)

      MyBase.New(xValue, yValue)
   End Sub ' New

   Public Overrides Function ToString() As String
      Return "Center= " & MyBase.ToString() & _
         "; Radius = " & mRadius
   End Function ' ToString

End Class
Point point1: [0, 0]
Circle circle1: Center= [0, 0]; Radius = 0
Circle circle1 (via point2): Center= [0, 0]; Radius = 0
Circle circle1 (via circle2): Center= [0, 0]; Radius = 0
point1 does not refer to a Circle
6.15.Polymorphism
6.15.1.Polymorphic Behaviour
6.15.2.Inheritance and polymorphism
6.15.3.Demonstrate polymorphism in Point-Circle-Cylinder hierarchy.
6.15.4.Late binding
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