Now let's take a look at actually implementing an interface, building one and implementing it. Pay close attention as I code this out because first of all I'm going to create an interface. And this interface has got a name, and some subroutines that I have to include when I use this interface. Then I'm actually going to go implement this interface and use it. So to start with I'm going to begin by creating a public interface and I'll call it Test. Now I simply list the subs and I'm going to say - DoThis () - and then - Sub DoThat (). What I've created here is an interface called Test that requires anybody who implements this interface to provide a DoThis subroutine and a DoThat subroutine. So what I will do now is I'll go back up here and if you remember our public class Lauren from previous examples. Right now it's inheriting from the Janet class right here and what I want to do now is have it use this interface Test. So the way I do that is to come down here and I type - Implements Test. Now you'll notice in my IntelliSense information here, it sees Test as an interface and you'll note especially the interface icon here. So I'm implementing Test, now you'll notice right away that I got a little blue squiggly line and this is indicating there is some sort of problem and if I mouse over this, it tells me that the - 'Class Test.Lauren' must implement 'Sub DoThat()' for interface 'Class Test.Test'. Which means it's saying - Hey! Wait a minute fellow: you said that you are going to implement this interface. Well if you are, then you are going to have to include for starters, DoThat. And so I'm going to go up here and I'm going to type - Public Sub DoThat. Now you'll notice my squiggly line's still there, right? So here's what I've got to do now. I've got to go back and tell it that this one implements and now it sees Test.DoThat. And then I need to end my sub. So now I've still got a squiggly line on the Test. Right? So I go back up here and I look at Test and it now says that I've got to implement sub DoThis. So I've got to go one more time, it's giving me a reminder - Public Sub DoThis() - and this one implements Test interface DoThis. And when I do that notice my squiggly line went away. Everybody's happy now; so what is happened now is this interface named the DoThis and the DoThat sub and then when I implemented the Test interface in this class it then reminded me or held me to the contract, if you are going to use this interface you are going to have to use both a public sub DoThat and a public sub DoThis. So that's the way interfaces work. Now let's go up here and create an object using this. I'm going to - Dim aa As New - and what was the name of our object down here that we implemented? Notice we are going to implement or we are going to instantiate an object off of the class Lauren, so we are going to say - As New Lauren. Now if I type aa and press period, you'll notice that I now can see these methods, DoThat and DoThis. So the interface basically brought me into a contractual agreement. Once I implemented it, it said that I would invoke all of the methods and procedures that it included. And that's exactly what I did. So now I can call DoThis if I would like. So that's an interface. Now these things are used extensively in the .NET Framework. You can use them to help provide standardization and provide contracts between your classes. So now that you've seen them, add these to your toolbox as a programmer, if you did not already know what they were. Now these are new to Visual Basic people. So you have to get used to these, we used to have to do some smoke and mirrors tricks with abstract classes to get to these things. And really what we are building down here is very similar those old abstract classes: we can just do it right here. So this is an interface. I hope it makes sense to you.
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