Question

I’m building a decent sized application in ASP.NET/VB.NET with various objects… I’ve never used interfaces before, and a fellow programmer balked when I mentioned this to him. Can anyone give me a quick overview on how they’re used, what they’re used for, and why I would use them? Maybe I don’t need to use them for this project, but if they would help, I surely would love to try.

Thanks so much!

Answer 1

Once you ‘get’ interfaces, OOP really falls into place. To put it simply, an interface defines a set of public method signatures, you create a class which implements those methods. This allows you generalize functions for any class which implements a particular interface (i.e. classes which have the same methods), even if those classes don’t necessarily descend from one another.

Module Module1      Interface ILifeform         ReadOnly Property Name() As String         Sub Speak()         Sub Eat()     End Interface      Class Dog         Implements ILifeform          Public ReadOnly Property Name() As String Implements ILifeform.Name             Get                 Return 'Doggy!'             End Get         End Property          Public Sub Speak() Implements ILifeform.Speak             Console.WriteLine('Woof!')         End Sub          Public Sub Eat() Implements ILifeform.Eat             Console.WriteLine('Yum, doggy biscuits!')         End Sub     End Class      Class Ninja         Implements ILifeform          Public ReadOnly Property Name() As String Implements ILifeform.Name             Get                 Return 'Ninja!!'             End Get         End Property          Public Sub Speak() Implements ILifeform.Speak             Console.WriteLine('Ninjas are silent, deadly killers')         End Sub          Public Sub Eat() Implements ILifeform.Eat             Console.WriteLine('Ninjas don't eat, they wail on guitars and kick ass')         End Sub     End Class      Class Monkey         Implements ILifeform           Public ReadOnly Property Name() As String Implements ILifeform.Name             Get                 Return 'Monkey!!!'             End Get         End Property          Public Sub Speak() Implements ILifeform.Speak             Console.WriteLine('Ook ook')         End Sub          Public Sub Eat() Implements ILifeform.Eat             Console.WriteLine('Bananas!')         End Sub     End Class       Sub Main()         Dim lifeforms As ILifeform() = New ILifeform() {New Dog(), New Ninja(), New Monkey()}         For Each x As ILifeform In lifeforms             HandleLifeform(x)         Next          Console.ReadKey(True)     End Sub      Sub HandleLifeform(ByVal x As ILifeform)         Console.WriteLine('Handling lifeform '{0}'', x.Name)         x.Speak()         x.Eat()         Console.WriteLine()     End Sub End Module 

None of the classes above descend from one another, but my HandleLifeform method is generalized to operate on all of them — or really any class which implements the ILifeform interface.