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‫Welcome back.

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‫In this video, it's all about inheritance.

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‫And we're going to go ahead and create a class, which I'm just going to call post.

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‫So a new class and it's going to be a post.

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‫So imagine that being a social media post, such as a Twitter post or a Facebook post or whatever kind

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‫of post.

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‫And the idea is that I want to inherit from post and I want to create something like an image post or

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‫later a video post, and those kind of things are going to enable us to understand the concept a bit

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‫better of inheritance, and you can apply that onto different objects and different situations in the

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‫future.

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‫So first of all, a post has a variable which I'm going to make private static in current post ID.

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‫So this one is going to be a field of that post and it's static.

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‫So it's available outside of this post as well.

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‫And it will be created once the application is started.

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‫Right.

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‫So what we can do is, first of all, create some properties.

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‫And now the idea behind properties, as you know, is they give you some more information about the

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‫object, right.

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‫So in our case, if I create an object of post, there are certain information that we really want to

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‫have.

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‫For example, we want to know the ID well as a admin, as a programmer, not that much as a user.

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‫And end user is not interested in the post ID, but as an admin or as the program you should be because

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‫every post should be identified and it should have a unique ID.

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‫So we're going to have IDs.

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‫We need a title.

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‫So for example, the Post has a title, maybe a description or a text, something like that.

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‫Then we need to know who sent that post and whether it should be public or not.

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‫Of course, there is a lot more to know about a post or there can be a lot more properties in a post,

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‫but we are going to keep it simple for now.

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‫So I'm going to create protected properties here and we have not used protected properties yet, but

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‫in the end protect means that it can only be used by this class, by the post class and any deriving

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‫classes, so classes which derive from post.

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‫So I'm going to go ahead and create the first one which is going to be the ID, so int I d and we're

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‫going to use get and set.

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‫Then another property.

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‫So I'm going to use Prop here and it should be a string and I'm going to call it title and as before

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‫it should be protected.

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‫Then another property and I'm going to use string again and this one will be send by user name.

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‫So who sent it and it's going to be selected as well.

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‫And finally, a property called is public.

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‫So it's a boolean because it can only have two values.

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‫So either it is public or it is not public.

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‫So we have simply these properties, right?

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‫So now we create a default constructor and there's something to know about the default constructor.

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‫If derived.

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‫If a draft class does not invoke a base clause constructor explicitly, the default constructor is called

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‫implicitly.

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‫That's why we create one here.

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‫So we create a public post, and now that post will be well, because we don't get any parameters here.

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‫It will be defined or we will set the values here, so ID will be zero.

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‫Then the title is for example, my first post, or maybe with empty spaces.

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‫First post like that then is it public?

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‫Well, let's say true because we want to see it and then send by username well sent by me.

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‫So then is new to in this case.

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‫So whenever we create a post now it's just going to be this post here.

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‫So it's going to be my first post, right?

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‫Then I want to have another instance constructor that has several parameters.

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‫So I want to create posts where I actually can define those things.

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‫I don't define the ID, but I can define the title.

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‫I can say whether it's public and whether it's sent by which username.

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‫So you can imagine that let's say you write a little social media program and you want to have the capability

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‫of posting, and then you need to send those information whenever you create a post.

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‫So a user creates a post, it gets an automatically defined ID, then it gets an automatically defined

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‫or it gets a defined title based on what the user has entered.

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‫It is public based on what the user has ticked, whether he decided to make it public or not, and it's

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‫sent by him.

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‫So that's just data that is given over whenever a post is created.

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‫So now let's create an instance constructor that has three parameters.

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‫So I'm going to create public post and here I'm going to use the string title.

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‫Bool is public and string send by username and in here I will set the ID and for that I will need something.

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‫So I'm just going to set it to zero now.

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‫But I will need an additional method which will always create a new ID for each post and we will see

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‫how that works in a second.

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‫So this title is going to be title.

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‫This sent by username is going to be sent by username with a uncapped letter here and this dot is public

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‫is going to be is public and not the property but this parameter.

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‫So now I set that I don't want it to be zero.

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‫The ID should be unique.

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‫So the best way is to create a method which is going to be protected and it's called get next ID.

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‫What that will do is it will simply return the next ID, which means current post ID and here we increment

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‫before that.

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‫So each time it's called, it's going to increment itself by one.

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‫So this one here, this current post ID will be increased by one.

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‫So now instead of setting zero here, we are going to call the next ID or get next ID method.

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‫Now what else would you like to have in such a program where you can post something?

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‫Well, I guess the capability of adjusting a post.

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‫So for now we created a post and we would be pretty unhappy if we cannot change that post.

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‫And well, that's something that does actually happen in I think what Snapchat or there you create a

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‫picture and then it's there.

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‫You cannot edit that picture, not sure whether you can edit the text, but here we want to be able

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‫to edit the text so we will create a new method public void update and that should take in the title.

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‫And the pool is public because if you think about it, what should the user be able to update?

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‫He shouldn't be able to update the ID.

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‫Neither should he be able to update the username because it's sent by him.

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‫So he has a username and it shouldn't have impact onto the update of a post.

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‫So in here we're just going to update the post and it means we're only going to change the title and

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‫change the boolean, which is whether it's public or not.

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‫And in here we simply say this title is going to be title, and this that is public is going to be public.

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‫So that means, as we have here, a post.

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‫A post is a blueprint.

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‫Well, this class is a blueprint of any post instance.

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‫So whenever we post something that is that self, that instance is the post.

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‫And if we change its title, we change the title of that specific post.

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‫And if we change, whether it's public or not, we change the publicity of that specific post.

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‫So that enables us to update the title and it's publicity of an existing post.

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‫So now the next one that I want to create is a virtual method override of two string that is inherited

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‫from system dot object.

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‫So System Dot object is a class that comes here in system.

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‫So we can use that.

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‫It's within C-sharp and we can simply use it.

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‫And there is a method called to string or actually there from there we can call the two string method.

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‫So.

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‫System.

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‫But object has a two string method and we want to override that because every single class so our post

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‫class as well is inheriting from that object class.

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‫So system that object is a class from which we can inherit.

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‫So in here that object, for example, we can inherit from that or we do actually every class inherits

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‫from that.

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‫So now what we can do is we can override one of its methods.

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‫So public override, string and two string.

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‫As you can see, it already proposes this.

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‫So it says returns a string that represents the current object that something that is within the object

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‫class.

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‫And as you can see there is something called return based to string.

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‫So the base class has a two string method and if we just do that then it will then just pretty much

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‫will mean nothing because we simply will use the two string method of the base class anyways.

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‫But we can change that so we can adjust instead of returning whatever the base class would return.

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‫We want to do our own thing, so we're going to use string format in order to format a string which

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‫is going to have certain information.

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‫So it's going to be the ID, it's going to be the title and who send it.

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‫So I'm just going to use this kind of information like that.

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‫So it's going to be this ID, so the ID, then this, the title, and finally this dot sent by username.

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‫So that's what is going to return.

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‫So whenever we use two string, it's not going to return simply some information about the object,

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‫but it's going to return it in the standard format or in our format that we have created.

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‫So this is our format.

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‫All right.

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‫So.

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‫Let's create an object of that class.

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‫So let's go ahead into our program and then here let's create a post.

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‫So post post one is new post.

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‫And here I can enter some information or I can leave it.

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‫So if I leave it, that's the default constructor that will be called.

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‫So that one here.

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‫And if I don't, then a different one will be called.

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‫So let's say I posted something.

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‫Thanks for the birthday wishes.

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‫So everybody wished me a happy birthday.

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‫So I'm just going to say thank you very much and I want to make it true because I want my friends to

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‫see it so it should be public.

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‫And then Dennis Pan, Utah, is the one sending it.

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‫Of course, we could have a user class which does all of the handling and we could simply check which

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‫users logged in or whatever.

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‫But for now we just use a hardcoded string here.

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‫So it's going to be Dennis, Utah.

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‫So that's a new post that we have here and now we can go ahead and write that onto the console.

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‫So W and I'm going to say post dot to string and here of course the post one.

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‫So our post instance, so this one is our post instance and I call the post one and it's going to write

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‫something on the console and as we want to see what it is, we need to realign here.

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‫So we just want to keep the console open so that we see what's happening there.

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‫And then we are, as you can see, one, thanks for this birthday, birthday which is by Dennis Panetta

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‫and this one is the ID of this post.

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‫So that means that our post here.

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‫This one gets a new ID and the new ID is going to be zero plus plus one or plus one, which means it's

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‫just one.

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‫So that's why we get this one here.

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‫So the ID is one, then that's the post info and that's who send it by Dennis Pan.

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‫So now we have a post and now let's go ahead and use inheritance.

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‫Because so far, except for maybe this two string here, there is actually no inheritance.

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‫So actually, just for you.

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‫So you know what I said earlier, virtual method override of the two string method that is inherited

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‫from system that object.

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‫So now let's create a new class.

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‫And that one will be image post because well, so far we can only post certain simple text, but in

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‫the future we also want to post images.

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‫And now that image posts should be a deriving class of our base class post.

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‫Because this class here is a very simple class and we want to go ahead and inherit from it.

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‫So in order to inherit from another class, you use colon and then you enter the name of the class you

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‫want to inherit from.

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‫So I want to inherit from post.

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‫And what that allows me is to use all of its functionality.

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‫That's something that's pretty cool because now I can use its properties, I can use its variables except

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‫for its constructor here.

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‫And yeah, so let's go ahead and do that.

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‫And let's extend the image post.

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‫So as you know, it derives from post and now it should have another property called image URL and to

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‫constructors.

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‫So that's what I want to add.

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‫So first I need a property here and it will be a string called image.

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‫You are l that will be the image url of the image post.

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‫So let's say we post something and there is an image in it.

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‫Then it's automatically or it should be an image post and it needs to have an image URL.

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‫So a location where that image is stored and that can be on our servers or it could be simply on the

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‫internet.

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‫So whatever is there, we have this or you need to have this image URL for an image post.

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‫Now let's create a very simple constructor, public image post

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‫just like that, nothing else.

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‫As you can see, there is nothing in there.

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‫I don't want to do anything in here.

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‫And then I create another post here or image post constructor.

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‫But this time I want some parameters in here.

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‫So it's going to be string title, string send by username, string image URL and actually u r l and

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‫bool is public.

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‫So I want to have all of those.

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‫And now in the image post I want to set the ID again.

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‫This dot id is equal to get next id and that's something that's pretty cool already.

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‫Where the hell is this ID coming from?

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‫And where is this get next ID coming from?

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‫Well, it's coming from post.

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‫So we are taking this method here, this protected method.

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‫We can simply call it in here, we can use it as if it is ours.

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‫So we don't even need to say something like post dot get next ID, we simply say get next ID and the

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‫same thing for this ID.

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‫So each image post has an ID, the same thing as the post itself.

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‫And now that's true for the title as well.

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00:16:57,090 --> 00:16:59,370
‫So title is going to be title.

217
00:17:00,510 --> 00:17:06,690
‫Then this dot send by username is going to be sent by username.

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‫And finally, this is public is going to be is public.

219
00:17:14,700 --> 00:17:16,320
‫Now, that's pretty cool.

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‫We can use those things.

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00:17:18,090 --> 00:17:18,720
‫That's great.

222
00:17:18,720 --> 00:17:24,240
‫And now we also have our own property, which is our image URL and we have that here.

223
00:17:24,240 --> 00:17:30,960
‫So whenever an image post is created, the image URL has to be given over as an argument.

224
00:17:30,960 --> 00:17:36,000
‫So we say this image URL is going to be the image URL.

225
00:17:36,270 --> 00:17:41,370
‫So on one hand, we have the ones inherited from post.

226
00:17:43,000 --> 00:17:45,090
‫So I'm gonna add that here.

227
00:17:45,100 --> 00:17:49,000
‫And on the other hand, we have the one that is our own member.

228
00:17:49,000 --> 00:17:53,230
‫So property image URL is a member of image post but not of post.

229
00:17:53,230 --> 00:17:54,670
‫And that's something that's important.

230
00:17:54,670 --> 00:17:58,600
‫So Post doesn't know about this image URL and it doesn't matter.

231
00:17:59,140 --> 00:18:05,170
‫But our image post knows about all of the properties of our post, so that's inheritance.

232
00:18:07,060 --> 00:18:09,970
‫Now, one little thing about this image post here.

233
00:18:10,270 --> 00:18:11,080
‫So.

234
00:18:11,970 --> 00:18:19,410
‫The constructors are required those two because neither constructor calls a base class.

235
00:18:20,080 --> 00:18:25,870
‫So we don't use this based out calling the constructor of the base class and the default constructor

236
00:18:25,870 --> 00:18:31,180
‫in the base class is called implicitly because we don't call it explicitly in here.

237
00:18:31,180 --> 00:18:37,390
‫So neither in this one and nor in this one, the one from the base class, the constructor.

238
00:18:37,390 --> 00:18:46,220
‫So this default constructor must be called or there must be a base constructor within our post.

239
00:18:46,300 --> 00:18:47,290
‫That's why I created it.

240
00:18:47,290 --> 00:18:49,780
‫Because you might have wondered, why do we need that?

241
00:18:49,810 --> 00:18:51,220
‫Why is it there?

242
00:18:51,250 --> 00:18:55,480
‫Well, it's required because we don't explicitly call it.

243
00:18:55,570 --> 00:18:56,680
‫That's on.

244
00:18:56,710 --> 00:18:58,360
‫And it will be implicitly called.

245
00:18:58,740 --> 00:18:59,320
‫Right.

246
00:18:59,950 --> 00:19:00,550
‫Great.

247
00:19:00,550 --> 00:19:01,840
‫So that's that.

248
00:19:01,840 --> 00:19:07,060
‫Let's go ahead into our program class and create one of those posts.

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00:19:07,720 --> 00:19:16,240
‫And I'm going to create an image post now and it's going to be a new image post and actually give it

250
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‫a name.

251
00:19:17,440 --> 00:19:19,150
‫I'm going to call it Image Post one.

252
00:19:19,900 --> 00:19:21,910
‫It's going to be a new image post.

253
00:19:22,540 --> 00:19:31,660
‫And I'm going to check out my new shoes because I bought some new shoes and they are freaking awesome.

254
00:19:32,230 --> 00:19:33,700
‫And who sent it?

255
00:19:33,700 --> 00:19:37,210
‫Well, Dennis Panetta was super hyped about his new shoes.

256
00:19:37,210 --> 00:19:40,510
‫And of course, he needs to have a link for those images.

257
00:19:40,510 --> 00:19:46,420
‫Well, he just uploaded the image, but the image itself has a link because it's stored somewhere in

258
00:19:46,420 --> 00:19:50,200
‫our storage, so or in our servers.

259
00:19:50,200 --> 00:19:56,020
‫So it's going to be a secure https and I'm just going to fake a link here.

260
00:19:56,020 --> 00:20:03,340
‫I'm just going to call it images, dot com slash shoes and well, he made it public.

261
00:20:03,340 --> 00:20:04,150
‫So it's true.

262
00:20:04,980 --> 00:20:08,850
‫And let's put it onto the next line so it's easier to read.

263
00:20:09,060 --> 00:20:15,120
‫So now we have our image post and what we can do with the image post now is to write something on the

264
00:20:15,120 --> 00:20:17,220
‫console again to see what's going on.

265
00:20:17,220 --> 00:20:23,940
‫And I'm just going to call image post 1.2 string and that's again something that's pretty cool.

266
00:20:24,120 --> 00:20:27,930
‫So we call this two string method on our image post one.

267
00:20:28,050 --> 00:20:30,690
‫And do you see each string method in here?

268
00:20:30,780 --> 00:20:31,730
‫I don't.

269
00:20:31,740 --> 00:20:37,740
‫And that's cool because we take the one from our post, so we inherit from post and now we take its

270
00:20:37,740 --> 00:20:40,110
‫method, which is called two string.

271
00:20:40,110 --> 00:20:41,730
‫And if we run that.

272
00:20:42,930 --> 00:20:46,050
‫Actually, we need to stop running it.

273
00:20:47,470 --> 00:20:48,790
‫Because we won't see it.

274
00:20:49,000 --> 00:20:51,150
‫There is a reed and it's gone.

275
00:20:51,160 --> 00:20:54,940
‫So we need to take this red line and post it right here.

276
00:20:55,210 --> 00:20:59,770
‫So let's run it again and it says, Check out my new shoes by Dennis Panetta.

277
00:20:59,770 --> 00:21:01,020
‫But where is the link?

278
00:21:01,030 --> 00:21:01,900
‫I need the link.

279
00:21:01,900 --> 00:21:03,190
‫Come on, give me the link.

280
00:21:03,640 --> 00:21:08,940
‫Well, it's not there because the two string method of our post doesn't know about links.

281
00:21:08,950 --> 00:21:11,310
‫It has no clue about links.

282
00:21:11,320 --> 00:21:12,340
‫It doesn't care about links.

283
00:21:12,340 --> 00:21:13,850
‫It doesn't need any.

284
00:21:13,870 --> 00:21:16,180
‫So a little challenge for you.

285
00:21:16,180 --> 00:21:19,360
‫And that's how we're going to finish the video for now.

286
00:21:19,450 --> 00:21:27,550
‫Please create a two string method within our image post that also informs us about the link.

287
00:21:29,750 --> 00:21:30,020
‫All right.

288
00:21:30,020 --> 00:21:30,970
‫I hope you tried it.

289
00:21:30,980 --> 00:21:33,590
‫So what I'm going to do is I'm going to keep it simple.

290
00:21:33,590 --> 00:21:43,580
‫I'm going to copy the two string from here into our image post, and I'm going to change the format

291
00:21:43,580 --> 00:21:44,660
‫just a little bit.

292
00:21:45,880 --> 00:21:49,420
‫I'm going to add a little statement in here.

293
00:21:49,420 --> 00:21:54,100
‫So too is going to be the link and three is still going to be the user.

294
00:21:54,100 --> 00:21:56,350
‫So we need the link here.

295
00:21:56,350 --> 00:22:09,100
‫So this dot image URL comma, so the order is ID title, the URL and then sent by user.

296
00:22:09,100 --> 00:22:12,880
‫So if you do that, we override from the base clause.

297
00:22:12,880 --> 00:22:20,890
‫So we override the two string from our post which overloaded from the system object.

298
00:22:20,890 --> 00:22:24,190
‫So you can see you can override it and override it and so forth.

299
00:22:24,190 --> 00:22:26,950
‫And we will see where the limit is or how we can limit that.

300
00:22:26,950 --> 00:22:28,540
‫So now let's run it.

301
00:22:29,440 --> 00:22:30,140
‫And we can see.

302
00:22:30,160 --> 00:22:31,210
‫Check out my new shoes.

303
00:22:31,210 --> 00:22:32,060
‫Here's the link.

304
00:22:32,080 --> 00:22:32,950
‫Dennis Panetta.

305
00:22:33,100 --> 00:22:35,590
‫So now i can click on the link in the console.

306
00:22:35,590 --> 00:22:35,950
‫I can't.

307
00:22:35,950 --> 00:22:41,530
‫But generally I could click on the link and I could see the image or my tool, my app, for example,

308
00:22:41,530 --> 00:22:43,630
‫could read that link and show the image.

309
00:22:44,740 --> 00:22:45,250
‫All right.

310
00:22:45,250 --> 00:22:49,110
‫So that's a first glimpse into inheritance.

311
00:22:49,120 --> 00:22:50,020
‫It was a long video.

312
00:22:50,020 --> 00:22:50,590
‫I know that.

313
00:22:50,590 --> 00:22:53,260
‫And inheritance is a lot more than that.

314
00:22:53,260 --> 00:22:55,600
‫And we will look into a lot cooler things.

315
00:22:55,600 --> 00:23:00,010
‫But first of all, we're going to go to a challenge in the next video.

316
00:23:00,010 --> 00:23:03,850
‫And so see you in the next video.