Public Class Form1
    '// Designer
    Private Sub Form1_Load(ByVal sender As System.Object, ByVal e As _
      System.EventArgs) Handles MyBase.Load
        Try
            Dim p As New Person("hans", Nothing)
        Catch ex As InvalidPersonException
            MessageBox.Show("Fehlerhafte Personenangabe!")
        Catch ex As Exception
            MessageBox.Show("Unbekannter Fehler!")
        End Try
    End Sub
End Class
 
Public Class InvalidPersonException
    Inherits Exception
    Private _MyMessage As String
 
    Public Sub New(ByVal Message As String)
        Me._MyMessage = Message
    End Sub
 
    Public Overrides ReadOnly Property Message() As String
        Get
            Return _MyMessage
        End Get
    End Property
End Class
 
Public Class Person
    Inherits Object
 
    Private _N As String
    Private _V As String
    Protected Sub New()
        MyBase.New()
    End Sub
 
    Public Property Nachname() As String
        Get
            Return _N
        End Get
        Set(ByVal value As String)
            _N = value
        End Set
    End Property
 
    Public Sub New(ByVal Vorname As String, ByVal Nachname As String)
        MyBase.New()
        If Nachname Is Nothing Then Throw New InvalidPersonException("do not" & _
          "set surname!")
        _N = Nachname
        _V = Vorname
    End Sub
 
    Public Shared Function GetInstance() As Person
        Return New Person
    End Function
 
    Public Shared Function GetInstance(ByVal N As String, ByVal V As String) As _
      Person
        If N.Equals("??") Then Return Nothing
        Return New Person(V, N)
    End Function
End Class