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‫Welcome back.

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‫In this video, we are going to cover abstract classes and therefore we are going to create a bunch

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‫of new classes.

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‫And it's important that you understand the concept of classes and also inheritance and polymorphism,

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‫because we are going to build on that.

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‫And what we start with is to create a new class.

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‫So let's create a new class.

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‫Here we go to Project Add class, and I'm going to create a shape class and that's going to be the shape

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‫CSS.

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‫Now, the idea is that we want to create a class of which we don't want to create any objects, so we

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‫won't don't want to instantiate shapes.

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‫We want to instantiate objects which are types of shapes but not shapes himself.

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‫So for example, a shape would be a cube or a shape would be a sphere.

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‫And I'm using 3D shapes here, right?

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‫Three dimensional shapes.

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‫And well, we are going to create classes which will inherit from shape, but we want to make sure that

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‫shape is an actual abstract class, which means that we won't be able to create an object of it, but

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‫we will use its systems or its methods and its properties.

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‫So let's get started.

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‫Let's make this shape abstract, first of all.

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‫And in order to do so, we can use the keyword abstract.

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‫So now it's an abstract class.

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‫Now let's go ahead to our program that sees and see that it is an actual abstract class.

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‫So let's create a shape.

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‫Shape one equals new shape.

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‫So when we try to do that, you can see that cannot create an instance of an abstract class or interface

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‫shape.

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‫And as our shape is an abstract class, we cannot create objects of it, so we cannot instantiate it.

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‫That's an important aspect here.

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‫All right.

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‫Now we will need a property, and I'm just going to create this property called name.

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‫So the shape needs a name and we have a getter, etc. In order to create this, I'm just using pre prop

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‫and then double tab in order to create a new property.

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‫So we've seen that in other videos.

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‫Now I want to have a method and the method that I want to use will be a virtual method.

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‫Virtual void get info.

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‫This virtual keyboard that you see here is used to modify a method property indexer or event declared

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‫in the base class and allows to be overwritten in the derived class.

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‫So this allows us to override the get info method in a driving class.

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‫All right.

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‫So that's the idea behind this virtual keyword here.

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‫So let's just add a statement here.

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‫So see w double tab in order to get controlled right line.

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‫And here I just want to write something like.

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‫This is a and then the name of the shape.

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‫So this is a name.

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‫And now the idea behind this is that I want to have a new line and then I want to have this statement.

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‫This is a and then the name of the shape, because whenever we create a shape, we can set the name

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‫of it.

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‫So we have a virtual void.

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‫Now, now we can also add an abstract method.

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‫Now let's do that abstract double volume.

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‫So what I want to calculate is the volume of a shape.

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‫Now, here, I will not implement this method.

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‫That's an important distinction here.

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‫I'm not going to implement it here.

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‫I'm just going to say, okay, whenever a class wants to inherit from me, it needs to implement a functionality

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‫for the volume method.

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‫All right.

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‫Now, we could, of course, call this one, calculate volume or stuff like that, but I'm just going

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‫to call this one volume.

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‫All right.

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‫So now that we have our shape class prepared, we can save it and we can create a new class.

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‫So the next class that I'm going to create is the cube class.

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‫So I'm just going to create Cube, which is a 3D shape.

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‫So now my cube will inherit from shape.

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‫Now, if I do so, you can see I get an error here.

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‫It says Cube does not implement inherited abstract member shape volume.

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‫So show potential fix this.

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‫All right, implement abstract class.

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‫If I do so you can see it implements this volume method with an override statement.

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‫So it says it's overriding whatever was defined in shape.

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‫And as shape is an abstract class and this method is abstract.

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‫As you can see, there is no method body.

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‫It's really just the declaration of the method.

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‫So now we can go ahead and of course implement something.

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‫You can see we throw an error here, not implemented exception.

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‫Of course we want to implement something in here.

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‫So let's implement a volume calculation in our cube class.

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‫Now in order to calculate it, what we will need is we will need a property which is going to be a length.

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‫So I'm just going to create this new property called length here, and I'm also going to add a constructor.

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‫So Public Cube and whenever I want to create a cube, I need to pass a length.

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‫So that's what I'm staying saying here.

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‫And while I'm at it, I'm also going to add a name.

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‫So as you can see, we're using inheritance here because name is not defined in cube, but it is defined

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‫in shape.

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‫So I can just set the variable name here and I'm going to set the length to the length that was passed

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‫to me.

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‫So the property length will be the same length as the length that is passed once we create an object

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‫of type.

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‫Q So that's the idea behind this variable.

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‫And next we can implement this volume method and we can simply return something.

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‫So it needs to return a double, right?

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‫So we need to return something that is based on double.

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‫And in order to calculate the volume of a cube and hereby I'm using a cube which has the same length

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‫on all sides.

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‫So I'm just going to say length to the power of three.

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‫So math, pulp, length three, that means that it's going to calculate length, times length, times

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‫length.

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‫So this is what our volume will be and it will return this value.

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‫Now we can go ahead and we can also implement this method called get info.

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‫So what I'm going to do is I'm just going to copy it and I'm going to now not use the virtual keyword,

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‫but override keyword because I want to override the get info method from my parent now and here.

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‫If I do so what I can do is I can also call the get info method from my base class, which means in

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‫this case it's also going to call get info from shape dot CSS.

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‫So it's going to call this method here.

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‫So meaning that will execute this code and then it will execute whatever code we add at the bottom of

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‫it.

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‫So I'm going to add a little text here and it's going to say the cube has a length of and then I'm going

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‫to pass the length here.

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‫So length, of course, I could also calculate the volume here, but I'm going to leave that to you.

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‫So if you want to do it, feel free.

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‫All right.

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‫So this is how we can.

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‫Go ahead and create a class that is going to inherit from one other class that is abstract.

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‫Now, as a little challenge for you and I'm just going to pause the video once, you should start with

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‫a challenge.

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‫So the idea is now create another shape, which is another class which is inheriting from shape, and

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‫the shape should be a sphere.

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‫Now implement the same type of functionality that you can see here for Sphere.

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‫All right.

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‫Good luck.

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‫Post the video and try to do that.

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‫All right.

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‫So I hope you tried it.

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‫I'm going to create a new class here and I'm going to call this class sphere dot CSS.

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‫And this class should be inheriting from shape.

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‫And of course, I need to implement my abstract class, which means that I need to implement this volume

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‫method.

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‫Now in here I can of course, again calculate the or have a property, but this time a useful property

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‫would not be the length, but it would actually be the radius, because we calculate the volume differently

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‫in the sphere than we do in a cube.

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‫And we didn't do it in shape because a shape by itself cannot have a volume right?

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‫If it's not defined as a Y, we cannot calculate the volume of it, let's say, because we don't know

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‫what kind of shape it is.

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‫Right.

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‫That's why we need those classes which inherit from shape and which implement the functionality.

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‫So now I can go ahead and create a constructor, public sphere, a double radius.

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‫So we need a radius and then we can go ahead and set the name of the sphere, which should be sphere,

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‫and we should have a radius property value.

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‫So we assign the radius that is passed to us as the property radius value.

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‫All right, now that we have that, we can calculate the volume.

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‫So now instead of throwing an exception here, I want to calculate the volume of my sphere.

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‫And in order to do so, I need PI and I need the following calculation.

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‫So math that pal radius to the power three and all of that multiplied with three divided by oh four

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‫divided by three.

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‫All right.

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‫So this is how we calculate the volume, and now we can go ahead and also implement the get info method.

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‫So I'm just going to copy get info from my cube.

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‫I'm going to be lazy.

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‫So copy this part here and implement the same thing.

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‫So we use the override keyword again, it's exactly the same name as it was in the shape class.

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‫And we use base code info here in order to call whatever was the method in here.

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‫So whatever was the method body in there and then instead of passing length or saying something about

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‫the length, we are going to say something about the radius and the cube.

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‫In this case, it's the sphere has a radius of radius.

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‫All right.

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‫Now that we have all of that, what we can now do is we can go ahead and create objects of all of those

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‫different classes.

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‫So I'm not going to say hello world here.

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‫Instead, I'm going to create a bunch of shapes.

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‫So I'm going to say, okay, please give me an array of shapes.

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‫And it's going to be a new sphere with a radius of four and a new cube with a radius of three.

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‫And in this case, actually, it's the length of three because Cube doesn't have a radius, it has a

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‫length.

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‫And then I want to execute something for each of the shapes.

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‫So for shape in shapes, I want to.

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‫Go through all of all of them in this case, just the two of them.

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‫But what I want to have is shape the info.

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‫So get info should be called and I want to write something like this.

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‫And in this case, zero.

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‫Will be the name and then I want to show the volume.

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‫So I want to have the name has a volume of.

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‫And then, of course, I want to know the volume of this piece that we're looking at.

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‫So shape the name and shape the volume.

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‫So here it's important that we call the volume method, right?

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‫It's not just a.

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‫Property.

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‫So we have console red line has a volume of in this case name has a volume of volume.

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‫So it will just calculate the volume.

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‫Okay, so now let's just test this.

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‫Let's just see what's going on here, what we have created and that we are so we have an empty, empty

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‫line here.

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‫Then it says, this is a sphere.

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‫The sphere has a radius of four.

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‫The sphere has a volume of 268.08.

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‫And then this is a cube.

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‫This cube has a length of three.

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‫The cube has a volume of 27.

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‫All right.

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‫So you can see that this is a very simple code that we wrote here, but it already explains or shows

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‫most of the functionality that we need to know about abstract classes.

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‫Now, the cool thing is we can also use some more keywords that we haven't used yet.

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‫And as this video is getting long enough, I'd say we do that in the next video.

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‫So see you there.