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‫In this lesson, you will learn how to create and implement your own interfaces with a concrete example,

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‫and you will get an idea of why interfaces are used, especially when our classes don't have a relationship

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‫with each other and therefore they don't share a base class.

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‫So inheritance as such is not an option.

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‫Imagine that we are working on a video game where the player can destroy stuff, but everything we destroy

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‫will have different behavior depending on what is destroyed.

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‫For example, destroying a chair will play some destruction sound and will spawn destroyed chair parts.

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‫But destroying a car will play an explosion sound, create fire and destroy other objects nearby.

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‫For our game, we have the following classes a chair that inherits from class furniture and the car

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‫that inherits from class vehicle.

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‫So let's look at those classes real quick.

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‫So we have this chair which inherits from furniture, and the chair just has a simple constructor here

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‫where we set the color as well as the material based on what is given to the object that is created.

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‫But now, of course, this class is inheriting from furniture, which is why we have those properties

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‫here, color and material that we just used in the chair class.

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‫And then we have the constructor here, which is the default constructor, where those values will be

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‫set by default.

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‫So the color and the material will be white and wood by default.

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‫And then we also have a simple constructor which uses the color as well as the material to set them

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‫by default.

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‫Okay, so there is nothing to fancy, but of course we also have a car and we want to be able to destroy

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‫the chair and the car, as I stated earlier.

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‫So let's look at the car real quick.

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‫So here we have the same story, a subclass car that extends vehicle where we set the car speed as well

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‫as the color.

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‫So now we are using, by the way, a simple constructor as we do it here.

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‫But of course, we could have used based here as well, passing the speed as well as the color.

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‫So that is also a valid option and we wouldn't have to use this in here.

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‫So there are two different ways, of course, to go about it.

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‫Okay.

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‫And then this car is inheriting from vehicle where of course, speed and color have to be defined.

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‫So let's look at the vehicle class and we can see here that this base class vehicle has a speed, a

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‫color, a default constructor, which sets those two values, speed with a 120 kilometers per hour and

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‫the color with white.

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‫And then we have the simple constructor which set the speed and the color based on the values that are

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‫given to the vehicle object.

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‫Also, of course, to the inheriting objects such as a car, for example.

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‫Okay.

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‫So now that we have all of those different classes and we saw how they are structured, let's look at

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‫the actual destruction feature.

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‫So what is the best approach to create such a destruction feature?

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‫If we think about it, we can't add a class to make our classes inherit from it because C-sharp is a

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‫single inheritance language and not a multi inheritance language we all already inherit from one class,

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‫so the car already inherits from vehicle and the chair already inherits from furniture.

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‫So it cannot inherit from something else.

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‫Like, for example, the vehicle here, you see, C-sharp doesn't allow this because it cannot have

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‫multiple base classes.

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‫A class cannot have multiple base classes in C-sharp.

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‫So plus there is no concrete relationship between a car and a chair to share one base class anyways

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‫because they are entirely different to two things, right?

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‫If we implement normal methods called the destroy method, for example, in each of those classes that

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‫we have here, it will be hard to maintain.

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‫What if we decide to change the destruction system entirely or add visual effects to our destructible

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‫objects in the future?

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‫It will be a pain to actually go through each class and modify it.

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‫Because in this case, we only have two subclasses, so to speak.

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‫Right.

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‫But imagine you have 50 or even 100 different classes, 100 different types of objects in your game.

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‫Then you would have to go through every single one of them and adjust the code accordingly.

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‫So that is really a burden and we don't want to go through that.

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‫That's why we need to find a better solution.

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‫What we need is a way to enforce our distractible behavior on every class that uses it, just like a

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‫contract.

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‫And if you have watched our video on interfaces, you know that they are contracts that we can create.

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‫So the best approach in this case is to use an interface and we will call it I Destroy Able.

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‫And any class that implements this interface will be forced to follow our destruction requirements and

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‫customize it at the same time, depending on the class itself.

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‫So let's go ahead and create such an interface.

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‫Therefore, you can go here to your project, add a new item, and then select interface right here

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‫and give it a name.

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‫So I'm going to call this one.

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‫I d destroy ble so you can see when using interfaces you add the I at the beginning of the name of the

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‫file to indicate that this is going to be an interface.

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‫So let's add this interface.

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‫So this interface will just have a property to store the audio file that will be run once we execute

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‫the destruction, which will be the destruction sound.

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‫And then we just have a method that will destroy an object and we're going to call this method destroy.

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‫It will not return anything, it will just destroy something.

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‫So it could, for example, return the graphics that you have.

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‫So the objects that you want to display once the item is destroyed, for example, the car is destroyed

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‫or the chair is destroyed and so forth.

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‫So let's now make sure that our classes are in fact going to implement this interface and then, of

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‫course implement the interfaces content, meaning the destruction sound as well as the destroy method.

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‫How can we do that?

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‫Well, let's go over to our car, for example, and here our car will need to add a comma here at the

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‫top of the class definition at the top and use this I destroy able interface like so now if you add

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‫that you can see that you get an error which says car does not implement interface member destruction

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‫sound as well as destroy so we can show potential fixes and implement all members.

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‫For example, this will create this automatic code for us.

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‫So it will create the void, destroy, able destroy and it will create a destruction sound for us.

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‫So that would be the auto generated version, but we can also do it manually.

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‫There's no problem with that.

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‫So here, for example, we can implement the destruction sound.

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‫And then what I want to be able to do is I want to have a property to store the destroyed objects nearby.

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‫So when a car gets destroyed, it should also destroy the nearby object.

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‫And this list is also going to be of type.

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‫I destroy able, which means it can store any object that implements this interface and we can only

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‫access properties and methods in that interface.

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‫So in order to create that, I'm going to create a public list of I destroy all objects and I'm going

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‫to call them destroy balls nearby.

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‫So now we can go ahead and extend our constructor.

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‫So on one hand, we want to make sure that we initialize the sound.

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‫So we make sure that we have an explosion sound.

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‫For example, let's say we have this sound called car explosion sound amp three.

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‫And then we want to initialize the list of destroy able objects.

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‫So this will, for example, just be a new list of destroyed objects, and then we just need to also

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‫implement the destroy method.

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‫So this I destroy.

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‫Well, here at the top you can see it's still not happy, it's still expecting us to implement the destroy

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‫method.

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‫So you see when you implement an interface you need to implement its members because the interface here

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‫has two members, we need to implement both of them.

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‫So that means that we need to go back here and we need to actually implement the destroy method.

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‫So let's really quickly do that in order to do it.

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‫What I want to add in here is going to be, first of all, two statements.

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‫I'm just going to use right line statements.

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‫I'm going to keep it simple because we're not creating a game here, but just trying to understand the

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‫concepts of interfaces.

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‫So when a car gets destroyed, we should play the destruction sound and create a fire effect.

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‫So here we are just mimicking as if we would actually play the sound and it will just say, okay, playing

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‫the car explosion amp three sound and then we create the fire.

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‫So everything is under fire.

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‫Everything is burning because the car is destroyed.

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‫So now let's go through every single destroy all nearby and actually destroy it.

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‫So here we're going to go through every single I destroy object that is inside of our list of destroyed

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‫balls nearby.

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‫We call it destroy all.

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‫So every single item is going to be a destroyed ball, which is basically just a local variable name.

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‫So we say, okay, the destroyed object that will implement the ID Storable interface will just be called

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‫destroy ball in our for each loop.

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‫So we iterate through it, which means we iterate through the collection, destroy balls nearby, which

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‫is a list of I destroy objects, basically objects that implement the ID stretchable interface and then

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‫we just call the destroy method.

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‫So basically we create a chain reaction here, destroying everything around everything that is destroyed

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‫and that is also a car and so forth.

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‫So in this case, let's say we have two cars next to each other and they have a bunch of chairs next

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‫to each other.

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‫So the cars will call this destroy method where they will destroy the items nearby because, well,

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‫it's a huge explosion.

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‫Right.

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‫There is a sound coming up and every item creates a sound.

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‫Now, you could, of course, create a timer that it needs until the actual explosion happens after

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‫something catches fire.

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‫But we're going to keep it simple here.

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‫So we're destroying the other cars, but also the other chairs.

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‫So each car will infect other items surrounding it that are nearby.

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‫And this could be, let's say, everything that is ten meters away or five meters away or however many

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‫inches away if you want to take the American system here.

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‫But that is basically what's going to happen.

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‫Now, let's look at the chairs, because the chairs are going to have to go through a similar approach,

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‫because we also want to make sure that a chair is destroyed, but the destruction of a chair will be

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‫very different.

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‫So here we will also add the interface.

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‫So the I destroy all interface and of course we need to implement the destruction sound and that will

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‫be a very different destruction because the chair will just fall apart and it will be shattering wood

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‫that you hear.

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‫So it will be a very different sound here.

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‫And then of course, we want to define the destruction sound inside of our constructor as well.

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‫So I'm going to say that the chair destruction sound should be played.

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‫It will always be the same.

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‫That's why I'm not adding it here in the declaration of the Chair.

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‫So I'm keeping it simple here.

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‫Of course, you could have different chairs that have different explosion sounds.

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‫Then you would add it here at the top as a parameter for your constructor.

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‫Okay, so now let's actually implement the destroy method.

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‫And in this case, what will happen is we will destroy something and we will, first of all, destroy

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‫the colored chair based on the color that the chair has.

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‫We will write that, then we will play the destruction sound.

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‫And then finally we are going to spawn chair parts.

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‫So in our case we're just writing it onto the console.

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‫But just imagine in a real game how you would do that, because the best way to destroy something in

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‫a video game is not to actually do the physical thing where you do all of the destruction, which is

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‫very difficult to build as especially if.

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‫Don't have a big team that does all kinds of things.

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‫Then you would basically just make a big explosion or destruction animation, and then you would spawn

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‫the destroyed parts of the individual parts that lay around.

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‫So you see here there is no chain reaction coming from this destroy method.

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‫So the destroy method implementation for the chair is very different to the one from the vehicle, but

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‫both of them inherit from the I destroy able interface and have to implement the destroy method and

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‫they can do it their own way.

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‫So basically interfaces allow us some sort of multi inheritance, even though it's not really multi

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‫inheritance.

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‫Okay.

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‫So now let's go ahead and go to our program, CSS, and actually use our newly created classes because

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‫well, otherwise it's boring, right?

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‫So let's go ahead and create two chairs.

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‫So we have an office chair which is going to be brown and plastic, and then we have a gaming chair

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‫which will be red and wood.

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‫And then let's also create a new car.

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‫So this car will have a speed of 80 and it will be blue and it will be a damaged car.

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‫And then we're going to add the two chairs nearby, this damaged car.

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‫So we add them as destroyed wheels nearby to our damaged car.

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‫So the office chair as well as the gaming chair will now be, if we look at it here as destroyed, it's

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‫nearby because when creating a car, this list will be empty.

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‫But then we can, of course, because it's a public list here, we can add items to it, which we do.

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‫We add destroyed all items to it.

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‫And why can we add chairs to our destroyed balls nearby?

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‫Well, because a chair implements this interface.

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‫That we called it tribal.

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‫This means that a chair is now going to be accepted as an object of type I destroy.

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‫Which means we can now add it as our disturbance nearby.

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‫So now we can go ahead and destroy the car.

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‫So let's just call the destroy method for our damaged car so the explosion can take part.

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‫The explosion sound can start and all of the good stuff.

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‫So let's run this.

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‫And of course, this will be more of an adventure game and not so much a game where you see actual 3D

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‫graphics or anything.

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‫So we play the destruction sound, car explosion sound, we create the fire.

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‫The brown chair was destroyed.

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‫We are playing the destruction sound of the chair destruction sound amp three.

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‫Then we are spawning the chair parts for our brown chair.

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‫Then the red chair was destroyed.

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‫We are playing the destruction sound of the chair destruction sound amp three and then we're spawning

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‫chair parts for our red chair.

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‫So you see, that's pretty much it.

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‫So that's how you can create your own interfaces and how you can use them.

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‫And I hope that you now understand what interfaces can do for you and the advantages of interfaces.

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‫So an important note here by interfaces are used for communication between two similar or non similar

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‫classes which do not care about the type of class implementing the interface.

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‫Just like how our car communicated with the chair to call the destroy method all because they just implemented

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‫the same interface as I earlier stated.

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‫So while interfaces might seem hard to understand at first glance, they provide us with great perks.

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‫Those perks are code readability.

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‫So an interface constitutes a declaration about intentions, so it defines the capability of your class.

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‫So what your class is capable of doing, if you implement the AI sortable, for example, you are clearly

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‫stating that objects of your class can be sorted then code semantics.

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‫By providing interfaces and implementing them, you're actively separating concepts and interface defines

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‫a behavioral model, a definition of what an object can do and separating those concepts keeps the semantics

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‫of your code a lot clearer.

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‫Then you have the code.

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‫Maintainability interfaces help reduce coupling and allow you to easily interchange implementations

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‫for the same concept without the underlying code being affected.

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‫And then we have design patterns.

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‫It's the bigger picture of using contracts, abstraction and interfaces pivotal for object oriented

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‫programming, so human understanding and complex system architecture.

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‫So it's really basically just to understand it better as a human being and then multiple inheritance.

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‫So interfaces can be our gateway to use multiple inheritance in C-sharp.

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‫So suppose you write a library and want it to be modifiable by users.

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‫You write interface and its class implementation.

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‫Other developers who will use your library can still write their own implementation class, which may

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‫use different technologies or algorithms that achieve the same result.

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‫This is also why we meet so many interfaces in libraries we use, but rarely feel the need to write

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‫our own interfaces because we don't write libraries ourselves.

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‫On a final note, the important thing is to understand how interfaces are implemented at this point.

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‫Of course, as we go through different technologies like WPF and ASP.NET and the C sharp master class,

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‫we will start using interfaces more, which will help you understand them better in the future.

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‫All right.

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‫So thanks a lot for watching this video.

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‫See you in the next one.