VB.Net Tutorial/Class Module/Class Cast — различия между версиями
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Текущая версия на 15:55, 26 мая 2010
Downcast: cast base-class reference to derived-class
<source lang="vbnet">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</source>
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