в 16:40, 26 мая 2010

2010-05-26T16:40:30Z

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2010-05-26T12:54:02Z

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==Demonstrate "is a" relationship==

<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>
<pre class=codeResult>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</pre>

==Use Is and As to convert a class to its implenented Interface==

<source lang="vbnet">Imports System
Interface Printable
Sub Read( )
Sub Write(ByVal obj As Object)
Property Status( ) As Integer
End Interface
Interface Zippable
Sub Zip( )
Sub Unzip( )
End Interface
Public Class Document
Implements Printable
Public Sub New(ByVal s As String)
Console.WriteLine("Creating document with: {0}", s)
End Sub
Public Sub Read( ) Implements Printable.Read
Console.WriteLine("Implementing the Read Method for Printable")
End Sub
Public Sub Write(ByVal o As Object) Implements Printable.Write
Console.WriteLine("Implementing the Write Method for Printable")
End Sub "Write
Public Property Status( ) As Integer Implements Printable.Status
Get
Return Status
End Get
Set(ByVal Value As Integer)
Status = Value
End Set
End Property
Private myStatus As Integer = 0
End Class "Document
Class Tester
Public Sub Run( )
End Sub "Run
Shared Sub Main( )
Dim doc As New Document("Test Document")
If TypeOf doc Is Printable Then
Dim isDoc As Printable = doc
isDoc.Read( )
Else
Console.WriteLine("Could not cast to Printable")
End If
If TypeOf doc Is Zippable Then
Dim icDoc As Zippable = doc
icDoc.Zip( )
Else
Console.WriteLine("Could not cast to Zippable")
End If
End Sub "Main
End Class</source>
<pre class=codeResult>Creating document with: Test Document
Implementing the Read Method for Printable
Could not cast to Zippable</pre>

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в 16:40, 26 мая 2010

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