Question

I understand the concept of interfaces, however I often find it difficult to find practical examples of how to use them. I have produced the following code:

Public MustInherit Class Deletion2
    Implements DeletionInterface2

    Public MustOverride Function Delete() As String Implements DeletionInterface2.Delete
    Public Function CheckDate() As Boolean Implements DeletionInterface2.CheckDate
        Return True
    End Function
End Class

Public Class System1Delete
    Inherits Deletion2
    Implements DeletionInterface2
    Overrides Function Delete() As String
        Return "System 1 Deleted"
    End Function

End Class

Public Class System2Delete
    Inherits Deletion2
    Implements DeletionInterface2
    Overrides Function Delete() As String
        Return "System 2 Deleted"
    End Function

End Class

Public Interface DeletionInterface2
    Function CheckDate() As Boolean
    Function Delete() As String
End Interface

Public Class Form1

    Private Sub Form1_Load(ByVal sender As Object, ByVal e As System.EventArgs) Handles Me.Load

Dim IDeletion As DeletionInterface2
        IDeletion = New System1Delete
        IDeletion.CheckDate()
        IDeletion.Delete()
        IDeletion = Nothing

        IDeletion = New System2Delete
        IDeletion.CheckDate()
        IDeletion.Delete()
        IDeletion = Nothing
End Sub

In the example above (in page load) I have used a reference to an interface to create an instance of an object, but I do not understand the true benefit of this.

Answer 1

The benefit of using an abstraction like an interface (or a MustInherit class) is that you can treat any object that implements the interface the same exact way.

For example, the System.Data namespace uses many such abstraction, meaning that implementing the different data providers is easier and since the core is using these abstractions, it doesn’t need to change as new implementations are added (things about all the different providers, built in and third party – SQL Server, Oracle, PostGresSQL, MySQL etc…).