Derived Class and Overrides : Overridable « Class Module « VB.Net Tutorial

1. VB.Net Tutorial
2. Class Module
3. Overridable

' compile with: vbc PolyExampleVB.vb
Class BaseClass
    Dim i As Integer = 5
    Public Overridable Sub Print()
        Console.WriteLine("i is {0}", i)
    End Sub
    Public Overrides Function ToString() As String
        Return i.ToString()
    End Function
End Class
Class DerivedClass
    Inherits BaseClass
    Dim d As Double = 2.1
    Public Overrides Sub Print()
        MyBase.Print()
        Console.WriteLine("d is {0}", d)
    End Sub
    Public Overrides Function ToString() As String
        Return MyBase.ToString() + " " + d.ToString()
    End Function
End Class
Class TestBaseDerived
    Public Shared Sub Main()
        Dim b As New BaseClass()
        Dim d As New DerivedClass()
        Dim bd As BaseClass = New DerivedClass() ' note this!
        b.Print()    
        d.Print()
        bd.Print()   
        Console.WriteLine("b: {0}, d: {1}, bd: {2}", b, d, bd)
        Console.ReadLine()
    End Sub
End Class