Mega Code Archive
Downcast
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Class Tester
Shared Sub Main()
Dim point1, point2 As Point
Dim circle1, circle2 As Circle
point1 = New Point(30, 50)
circle1 = New Circle(120, 89, 2.7)
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 Circle) Then
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
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