Question

What is the difference of using interfaces like …

I have an interface

Public Interface IProDataSource

    Function read() As Integer

End Interface

Then a class

Public Class DataSource : Implements IProDataSource

     Function read() As Integer Implements IProDataSource.read

         some code...

     End Function

End Class

Then I use this the next way … but what is the difference? … both approaches are working …

Dim obj As IProDataSource = New DataSource
obj.read()

vs

Dim datas as new Datasource
datas.read()

The only difference I have notice is that if the method is declare private it will be visible using the first approach only.

Thanks for any comments !!!

Answer 1

If obj is a DataSource, you cannot get to the non-Interface methods of the DataSource through a variable declared as the interface. Otherwise, in your example, there is really no difference.

Notice the “is a”.

IList is a good interface to check out. Many objects take or use IList as method parameters. (To see all the classes that implement IList, open the “Object Browser”, browse to IList and expand “Derived Types”.) For example, if I was implementing a Windows.Forms control, instead of forcing you to pass a list as an Array, List, Collection, or some other object, I could specify IList and any class that implements that interface can be used by the control.

A practical example, the DataSource property of a ComboBox accepts any object that implements the System.Collections.IList interface, such as a System.Data.DataSet or an System.Array.

Interfaces Overview

Interfaces, like classes, define a set
of properties, methods, and events.
But unlike classes, interfaces do not
provide implementation. They are
implemented by classes, and defined as
separate entities from classes.

An interface represents a contract, in
that a class that implements an
interface must implement every aspect
of that interface exactly as it is
defined.

http://msdn.microsoft.com/en-us/library/s3et34z3(VS.80).aspx