Public Class Form1
 
    Private mFahrzeug As Fahrzeug = Nothing
 
    Private Sub Button1_Click(sender As System.Object, e As System.EventArgs) _
      Handles Button1.Click
        mFahrzeug = New Fahrzeug
    End Sub
 
    Private Sub Button2_Click(sender As System.Object, e As System.EventArgs) _
      Handles Button2.Click
        If mFahrzeug IsNot Nothing Then
            '...
        Else
            Debug.WriteLine("Kein Fahrzeug ausgewählt")
        End If
    End Sub
 
End Class