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‫Instructor: Hi.

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‫Within this lecture we are going

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‫to start working on variables.

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‫So, if you haven't heard the term variables before,

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‫you're gonna learn it because you are going to need it

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‫in every kind of programming language that you

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‫will ever learn from this point on.

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‫Okay? So, why do we need variables

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‫and what are variables anyhow?

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‫So, it's spelled like this, variables,

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‫and beware of the two slashes that I have put over here

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‫in order to take a note.

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‫You can do the same thing as well.

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‫And as you can see, I cannot write like this.

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‫I'll get an error because it's not a word.

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‫It's not a comment. It's not a code.

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‫It's just a comment when you put two slashes in front of it.

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‫Okay? So, what is a variable?

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‫It's kind of an object to save values.

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‫For example, remember, we have done something like this.

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‫We have done five minus applied by two, I believe.

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‫Now, I'm doing 10 plus 20, or 10 multiplied by 20,

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‫and we get 200 out of it, right?

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‫So, maybe I want to store those values

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‫in variables, in some objects.

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‫So, why do we want that?

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‫For example, we may want to use it more

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‫than once or maybe we don't even know what the number

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‫that we are going to be multiplying is going to be,

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‫like, for example, the age of the user.

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‫So, suppose that age of the user is 20

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‫and I'm going to multiply the age of the user by 10.

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‫So, I can create a variable like this.

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‫So, this variable is an integer type.

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‫So, of course, there are multiple types

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‫of variables and this is an integer.

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‫Integer means a whole number. It's a number, okay?

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‫It doesn't have a decimal.

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‫It's just a number like one or two or five or 20.

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‫So, in order to create a variable,

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‫all you have to do is just write "int" or the type

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‫of the variable and the name of the variable, okay?

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‫I could have called this anything, not only age,

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‫but I could have changed that if I wanted

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‫to create an in integer.

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‫And then, with an equal sign, you just give the value.

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‫For example, once I do that, I can just delete the 20

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‫and I can write "age" over here,

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‫and Android Studio will know to multiply 10 by 20

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‫when I run this.

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‫As you can see, we still get the 200 out of this equation

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‫because age now represents 20.

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‫Now, I can use age in any other line as well.

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‫Like, I can divide the age by five. I will get four.

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‫So, as you can see, once I define a variable,

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‫I can use it in multiple places, so it's an advantage,

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‫and maybe I'm getting this value from internet.

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‫Maybe I'm getting this value

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‫from user via text field or something.

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‫So, let me create something like X is five, Y is 10, okay?

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‫And let's try to do Y divided by X.

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‫So, can I do that? Of course I can.

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‫As you can see,

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‫we still have the result of two 'cause I'm dividing 10

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‫by five over here.

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‫So, let me try to do that, 11 divided by five.

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‫What will I get? I still get two.

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‫So, it's a little bit odd, do you think?

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‫Because 11 divided by five is not a whole number.

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‫So, let me do this with calculator.

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‫If I divide 11 by five, I will get 2.2.

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‫I should get that in here as well, right?

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‫But, remember what I said about integer.

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‫Integer is a whole number. It doesn't have any decimals.

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‫So, when I divide an integer by integer,

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‫exactly what's gonna happen

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‫is to create another integer, right?

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‫So, if I want to get something with decimals,

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‫then I would work with double, or float.

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‫So, these are variables as well.

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‫Like, I can just say something like double Z

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‫is equal to 5.0.

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‫So, this is still five, but with 0.0. Okay?

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‫So, let me create another, like, 11.0.

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‫So, these are numbers as well and these are 11

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‫and five as well,

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‫but rather than just creating them, like integers,

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‫I have created them as doubles.

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‫So now, if I divide A by zet, what will I get as a result?

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‫So, let me try it and see.

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‫Let me run it from here, or right-clicking to domain,

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‫and as you can see, we have 2.2.

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‫Because the result of this equation is also a double,

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‫I'm actually dividing a double by a double

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‫and I'm getting the decimals like this.

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‫So, you will come across in situations where you will need

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‫to work on doubles because you will have,

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‫you will need some kind of decimals,

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‫but also, you will come across with situations

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‫where you will need to work with integers

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‫because the result, or the number itself,

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‫would have to be integers or longs.

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‫Okay? And these are all just numbers, right?

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‫So, maybe you get confused at this.

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‫What is a long? What is a float?

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‫So, let me show you.

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‫As you can see,

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‫if you can just search for "int, float, double Java,"

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‫you will come across with a table like this.

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‫So, we have this number types in Java, like integers,

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‫long, float, doubles, okay?

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‫And these are all just numbers,

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‫but they have different capacities like sizes,

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‫32 bits, 64 bits.

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‫As you can see, you can store much larger values

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‫with doubles rather than floats and much larger values

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‫with longs rather than integers,

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‫and if you are looking for a very big number to work with,

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‫then go for long and double and if you're working

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‫with small numbers, you can go for float and integers.

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‫Don't be confused by them.

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‫We're going to do a lot

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‫of examples during the lectures, okay?

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‫I'm just showing you this as an example

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‫so that you won't get confused

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‫about integers or floats or longs or doubles.

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‫These are just numbers

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‫and we have different number types, that's all.

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‫So let's, for example, try to do something like this.

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‫Let's create a long and call this "My Long,"

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‫with camel keys of course,

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‫and I'm going to give 10 as a value.

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‫Of course, you can print this out.

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‫You can do whatever you may want to do with it,

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‫like dividing it by five,

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‫and you will still get two as a result.

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‫Over here, it won't change the outcome of the situation.

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‫Of course, we can do this with float as well, like 10.0,

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‫but in case you get an error like this over here,

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‫it means that looking for float, but you gave me doubled.

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‫So, you have to be as explicit as possible over here,

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‫which is why they invented something like this.

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‫If you put F at the end of the value,

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‫it means that it's a float.

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‫If you don't put it, it's a double. Okay?

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‫So now, under Android Studio actually understand

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‫this is a double.

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‫So, we're not going to spend so much time over here.

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‫All you have to understand,

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‫these are just numbers and there are some,

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‫several types in Java.

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‫Let's continue within the next lecture.