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USING AS, IS and cast

Posted By:SanthoshNathan       Posted Date: December 14, 2010    Points: 15    Category:    URL: http://www.dotnetspark.com  

AS, IS and cast

Imports System

Public Class MainClass

    Shared Sub Main()
        Dim doc As New Document("Test Document")

        ' only cast if it is safe
        If TypeOf doc Is IStorable Then
            Dim isDoc As IStorable = doc
            Console.WriteLine("Could not cast to IStorable")
        End If

        ' this test will fail
        If TypeOf doc Is ICompressible Then
            Dim icDoc As ICompressible = doc
            Console.WriteLine("Could not cast to ICompressible")
        End If
    End Sub
End Class

Interface IStorable
    Sub Read()
    Sub Write(ByVal obj As Object)
    Property Status() As Integer
End Interface

Interface ICompressible
    Sub Compress()
    Sub Decompress()
End Interface

Public Class Document
    Implements IStorable

    Public Sub New(ByVal s As String)
        Console.WriteLine("Creating document with: {0}", s)
    End Sub

    Public Sub Read() Implements IStorable.Read
        Console.WriteLine("Implementing the Read Method for IStorable")
    End Sub

    Public Sub Write(ByVal o As Object) Implements IStorable.Write
        Console.WriteLine( _
          "Implementing the Write Method for IStorable")
    End Sub

    Public Property Status() As Integer Implements IStorable.Status
            Return Status
        End Get
        Set(ByVal Value As Integer)
            Status = Value
        End Set
    End Property

    Private myStatus As Integer = 0
End Class


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