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‫Welcome back.

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‫In this video, I would like to show you properties and teach you how properties work.

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‫And because one video would be too long and I created a video in the past about properties and it was

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‫a little too confusing as it seemed.

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‫I decided to break it down and rerecord it because it just wasn't good enough as it seems.

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‫So if you find another video which is totally confusing, it doesn't help you at all.

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‫Then please let me know because I want this course to be the best course out there.

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‫All right.

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‫So what we need to do is, first of all, create a new class.

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‫So let's go to project and add a new class, because I want to teach you the fundamentals of properties

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‫because they are an important aspect or an important concept that we're going to use a lot.

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‫That's why it's really important that you understand the whole breadth of it.

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‫So we start by creating a new class and I'm going to call this class box.

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‫All right?

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‫So just be very simple class.

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‫So this box class is going to just be a class that has a certain amount of variables.

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‫All right.

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‫So, for example, just want to calculate the volume of the box based on its length, its height and

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‫its width.

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‫All right.

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‫So let's just create those variables, and I'm going to make them public for now.

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‫All right?

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‫I'm going to make this one public length, then another, and this one will be the height, and then

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‫we need the width.

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‫And finally, I want to also have the volume.

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‫So the volume will be the end result of this box.

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‫All right.

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‫So now I have a bunch of variables.

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‫Now, those variables are not simple variables.

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‫They are, in fact, member variables, which means that they are the variables on the level of the

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‫class, in this case of the class box.

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‫So they have a direct impact on the whole appearance of the box or the whole structure of a box, so

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‫to say.

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‫All right.

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‫And we're going to see how we can use member variables in a different way or even a different structure,

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‫which is even safer.

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‫Because the problem here by is that they are public, so they're not safe.

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‫We will see how we can fix this.

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‫So first of all, let's go ahead and create a new method here.

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‫And I'm just going to call this one display info, because the idea behind it is that it will just display

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‫the length, the width, the height, and then it will calculate the volume and tell us how big the

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‫volume is.

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‫All right.

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‫I'm just going to write a short right line statement.

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‫So I enter CW double tab, which creates this console right line statement here for me.

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‫And in here I'm just going to say something like length is going to be the first entry and height is

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‫going to be the second entry.

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‫So I use it like this and with is the third entry.

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‫So the volume is and then I have the fourth entry.

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‫All right, so this is my whole right line statement and then the variables that I want to use is length,

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‫height.

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‫With.

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‫And volume.

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‫Now, volume is something that I need to calculate based on length, height and width.

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‫So I'm just going to do that.

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‫I'm just going to say the volume is the length multiplied with the height multiplied with the width.

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‫Doing so creates this volume or calculates the volume because the volume is the result of this calculation

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‫here.

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‫Length, time, side times, width, it's going to be the volume.

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‫All right.

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‫So now let me split it up into lines so it's a little more readable.

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‫All right.

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‫So now we have this method display info.

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‫Now let's go ahead and save this file and go to our program keys.

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‫Here we are going to use this class.

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‫We're going to create an object of this class.

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‫How do we create objects?

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‫Well.

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‫So I create a new object of it.

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‫I'm going to call this one box and it's going to be a new box.

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‫So this is how you create an object of a class or an instance of a class.

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‫So I'm creating an instance of this class box.

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‫So pretty much a variable of type box and box is what we created ourselves.

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‫Now what I can do is I can assign the values to it so I can go ahead and say, okay, the length is

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‫going to be three, then the height is going to be four and the width is going to be five, something

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‫like that.

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‫Of course, I need an equal sign here as well in order for this to be correct code.

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‫Now, what I can do is I can just go ahead and call box dot.

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‫Display info.

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‫So that's pretty cool.

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‫I don't need this bright line statement here anymore.

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‫I can now save this file and execute it.

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‫So let's run this file and it will display us the info in the console.

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‫So that we are length is free and height is four and width is five, so the volume is 60.

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‫All right.

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‫So that worked out.

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‫That's great.

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‫So this display info worked out and it just displaying the details that we wanted.

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‫Now what we could do is we could change the values or what we can change the values of the member variables

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‫of our box class.

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‫And we can do so because they are public.

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‫Right?

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‫So this one is public.

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‫This one is public.

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‫This one is also public.

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‫So all of them are public.

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‫Now, this is very insecure code because at this point, if you write member labels which are totally

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‫public, everyone can change them at any point.

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‫So everyone who can create an object or every class that can create an object of box, we'll be able

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‫to change all of those values of that instance of the box.

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‫So everyone was access to this box can change it now.

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‫And that is something that can cause a lot of problems.

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‫Go further down the road, right when you program and a team and stuff, then it can really become cumbersome

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‫to do it like this.

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‫So there are better ways.

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‫There are cleaner ways to implement it because maybe you don't want the length to be adjustable, maybe

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‫you want the length to have a certain value.

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‫No one can adjust it.

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‫Then what you could do is you could make this.

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‫Verbal privates.

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‫So my member variable length is going to be private and I'm just going to assign a default value of

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‫three to it.

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‫So now every box that I create will have the value for the length of three.

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‫So every box will have a length of three inches or meters or whatever the metrics are that you're using.

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‫So now I cannot assign length anymore.

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‫So you see, I get an error here.

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‫Box length is inaccessible due to its protection level.

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‫So we added the protection level by making it private.

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‫So now we cannot adjust it anymore.

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‫So how can we still change it?

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‫Well, we can't.

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‫Not that we're this way.

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‫So we need to implement something.

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‫We need to implement an alternative way to change the length of the box.

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‫All right.

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‫In order to do so, what we can do is we can implement something called setters and getters.

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‫So in this case, we cannot even access the length of the box anymore.

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‫So let's say I want to write the length.

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‫So I want to console right line box length is and then just going to access box dot length.

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‫As you can see, my ID doesn't even show me the variable.

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‫I can't access box dot length so I cannot change it.

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‫But I can also not read it.

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‫All right.

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‫So I can neither get it nor set it.

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‫So this is setting and this is getting the variable.

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‫These are very important terms setting and getting, because now what we can do is we can create methods

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‫in our box class which will allow us to set or get the variable length.

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‫So let's just do that.

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‫Let's create a.

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‫Sutter so public.

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‫Voit set length.

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‫So this variable will set the length.

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‫Now, what will it set it to?

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‫Well, it needs a variable or a parameter here.

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‫It needs a value here that it can set it to.

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‫So it's just going to.

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‫Need an integer here, and I'm just going to call this one length.

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‫So it will set the length.

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‫Now I will set length, equal length.

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‫Now, this is confusing and it's also incorrect.

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‫So I get a warning here.

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‫Don't even get an error here, because as you can see, the colors are different, right?

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‫So this color and that color are slightly different.

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‫This one is this very light color and this one is a darker blue color.

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‫So what is going on here?

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‫Because we are using the same word here.

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‫We're using length here.

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‫We're using length here and here, here as well.

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‫So this length here is actually this or should be this length here at the top.

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‫So if I want to do it correctly, I can use this this keyword to it.

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‫By doing so, I say, okay, I want to change the length, which is.

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‫Parts.

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‫Of this class called Box.

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‫So I want to change the length of this object.

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‫So in this case, of the object that is created of the class box.

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‫All right, so whatever length I'm getting assigned.

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‫So whatever length is passed when set length is called.

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‫This method will be.

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‫This variable here, and it will be set to the length, which is my private member variable of my box.

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‫This is very important because what I can do now is I can now go ahead and change the length of the

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‫box by doing so.

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‫Set length.

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‫I can also set the length to, for example, three and now run the code again and it will work perfectly

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‫fine.

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‫And let's see.

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‫All right.

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‫There we are.

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‫Length is free.

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‫Height is four and so forth.

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‫All right.

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‫So now let's say I don't want to have three because it was the default value.

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‫Now, let's say I want to have the length as four, and now we can see it's the working and the volume

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‫also has adjusted.

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‫So it even worked for the calculation.

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‫So that's great.

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‫So now we can set a variable which is a member variable of a class.

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‫So that's important.

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‫We're talking about the different class.

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‫It's not in the same class.

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‫Now what we can do is we can try to access this length because it's private, right?

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‫So how could I access it?

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‫Because maybe I really need this variable here somewhere.

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‫I want to access the length, but I can't do it.

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‫So what I can implement is something called a getter.

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‫So a get length public.

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‫And in this case the type has to be the same type as the variable that I want to return.

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‫And in this case, I want to return the value of this length or I want to return the length itself,

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‫right?

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‫So it's of type int.

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‫So I need to return an int type for this method.

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‫So this one will be get length and this is also the convention to use the name, get with the capital

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‫G and then the name of the variable that you want to get.

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‫And in this case I want to get the variable length and now you just return the length.

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‫Now, in order to be more precise, to return this dot length, of course you could just write the length,

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‫but when you add this, then it's perfectly clear that we're talking about the member variable here.

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‫So we're talking about the variable that is on the highest level of this class.

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‫So it's not within any method or so you couldn't even access it in this way.

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‫But here it's this particular length that we're talking about.

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‫So if I click on it, you can see my ID automatically marks it.

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‫And it's also marking this length here at the bottom.

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‫So now I can get the length by using get length by using this public method.

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‫And it's important that it's public because if it wasn't public, then I couldn't access it.

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‫So in this case, I'm saving the box again, and now I'm getting the length by calling this method get

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‫length, and now it suddenly works again.

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‫So now I can go ahead and of course write it correctly here as well length and let's run it again.

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‫And it's going to say box length is.

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‫And in this case, it's four.

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‫All right.

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‫So this is just the preparation for properties, but it's an important concept.

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‫Setters and getters, this is something that you are going to see quite a bit as well.

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‫So it's a totally fine approach, but there are a lot easier and faster approaches.

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‫So this is just one way to do it.

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‫But I'm going to show you two or even three other ways to make it even quicker and to have the same

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‫type of protection.

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‫Because what we're doing here is called encapsulation.

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‫So we are encapsulating the axis of our length.

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‫The definition of Wikipedia is that encapsulation refers to the building of data with the methods that

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‫operate on that data, or the restricting of direct access to some of an object's components.

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‫So that's exactly what we're doing.

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‫We are restricting the access to this component called length, which is part of an object or our class

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‫box of which we can create objects.

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‫All right.

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‫And we create these setters and getters in order to still adjust them.

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‫Now, the beauty is that you can define how you want to encapsulate.

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‫In this case, I made both of them public.

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‫But what if I don't want them to be public?

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‫What if I want this to be?

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‫Not suitable.

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‫So let's say I don't want anyone to be able to set the length of my box.

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‫So what I could do is I could make this one private.

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‫So now only.

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‫Classes that inherit from our box or the box itself will be able to set the length from outside.

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‫We will not be able to set the length anymore.

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‫So setting length here, this line of code is not working anymore because I decided, okay, if anyone

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‫wants to set the length, I wanted to only be the class itself or inheriting classes, but not classes

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‫outside of me.

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‫This is something that you can directly modify from here.

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‫You could also say, okay, even getting the length would not be allowed outside of here.

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‫All right.

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‫But now the cool thing is you can go ahead and adjust those.

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‫So let's say somebody wants to get the volume.

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‫And now at this point, we haven't set the volume yet.

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‫So what we can do instead, we can go ahead and say public int, get volume.

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‫And now if anyone wants to get the volume, we're not just going to return volume, but what we will

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‫do is we will return.

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‫This dot length multiplied with this dot height multiplied with this dot width.

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‫So if anyone wants to get the volume, they will not get the volume directly.

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‫So not get access to this variable directly, this volume variable, but they will actually get the

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‫result of the calculation.

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‫So now if I save this and instead go ahead and here I use get volume, then boxes volume is and now

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‫it will display the volume of the box.

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‫So let's say boxes, volume is 60.

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‫So now generally what we do with these setters and getters is that we don't give access directly to

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‫the variable to the member variable, but we only give access to a method which then can adjust the

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‫variable and we can ourselves decide how we pass this value, so how we hand out the value in this case

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‫with get volume, we decided, okay, we don't want to give you the volume itself, but we want to give

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‫you the result of a calculation.

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‫Or we could say, okay, if anyone wants to get the volume, we are going to say it's going to be volume

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‫times two or something like that.

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‫Or if anyone wants to set the length and it's something negative.

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‫So let's say we make this public again, public void, set length, and now we double check if length.

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‫Is less than zero.

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‫We're going to throw an error, throw new exception size or this one, a length should be higher than

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‫zero.

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‫All right.

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‫So if length is less than zero, then we throw an exception and this will just crash our program.

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‫So this line will never be executed.

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‫So now let's try this.

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‫Let's go to our program and set our box length to a negative value.

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‫Let's set it to minus four.

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‫Now we run it again and we will see that we get an exception.

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‫So our program crashes and we get an exception here saying.

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‫System exception length should be higher than zero.

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‫So you see, with throwing the exception, we can throw our own exceptions.

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‫We can even say what the exceptions should say and it should be meaningful.

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‫It should be something that is useful and makes clear what the error is.

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‫In this case, we created an error because we set the length to something that is less than zero.

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‫All right.

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‫So that's the power of these setters and getters, because you might wonder, why would I need those

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‫setters and get us?

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‫Why can I not just simply access the length directly if I just have setters and getters?

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‫Well, now you see it, you can actively decide what will be set and what will be forgotten.

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‫If somebody tries to access this variable and change it, or even just retrieve it.

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‫All right.

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‫So this was a lot longer than I had anticipated, and I was planning on doing this video.

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‫But I really wanted to make everything clear because this is going to be an important stepping stone

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‫for the next concept, which is going to be properties.

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‫So you're going to see how we can sum this all up or make it a lot shorter by using properties.

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‫So I'd say let's go to the next video where we're going to check out how to use properties and how they

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‫relate to what we have learned in this video.

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‫I hope it made sense.

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‫If you have any questions, please let me know.

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‫And yeah, just write a comment in the course discussions.

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‫And by the way, thanks a lot for everyone who gives feedback because it really helps me to make the

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‫course better.

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‫If you just passively watching this course, it's totally fine.

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00:19:40,590 --> 00:19:46,860
‫But I really appreciate if you have feedback and it's constructive and really helps me to know at which

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‫point something isn't clear.

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‫Because if you just say, okay, this video is complete garbage, then it will not be as useful as if

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00:19:53,310 --> 00:19:58,950
‫you say, okay, I didn't understand concept A at minute five or something, then I understand a lot

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‫better what the problem is.

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‫So thanks again and see you in the next video.