1
00:00:01,860 --> 00:00:04,560
In this lecture, I'm going to talk about variables.

2
00:00:05,100 --> 00:00:07,080
OK, so what are variables?

3
00:00:07,620 --> 00:00:15,270
Variables are used to store information, something like a number letter, a sentence or a combination

4
00:00:15,270 --> 00:00:15,810
of these.

5
00:00:16,510 --> 00:00:19,970
It is a piece of memory segment where the data is stored.

6
00:00:20,490 --> 00:00:25,220
First, we're going to look into the declaration and definition of a variable.

7
00:00:25,740 --> 00:00:28,950
So how to declare a variable and what it means.

8
00:00:29,430 --> 00:00:32,850
So to declare a variable in Java is the following.

9
00:00:33,330 --> 00:00:40,680
You need to type and data type first, then the variable name and a semicolon to the end of the line.

10
00:00:41,310 --> 00:00:43,490
We don't assign any value to it.

11
00:00:43,500 --> 00:00:47,210
Here, let me show you how it works in practice.

12
00:00:47,550 --> 00:00:49,740
So we created this program previously.

13
00:00:50,100 --> 00:00:53,670
Now let's delay the system that outdate print and online here.

14
00:00:56,470 --> 00:01:08,050
And instead, Tiepin and a number of followers and a semicolon, this variable can represent a number

15
00:01:08,050 --> 00:01:13,860
of YouTube or Twitter followers, or we can use another name like number of countries.

16
00:01:14,260 --> 00:01:16,860
And here is used for whole numbers.

17
00:01:17,440 --> 00:01:24,220
As you can see, the variable name is great because it isn't used and it doesn't have a value.

18
00:01:24,700 --> 00:01:31,600
So how we assign a value to this variable, that's what is called definition.

19
00:01:32,080 --> 00:01:33,110
It is very simple.

20
00:01:33,610 --> 00:01:41,040
First, the data type than the variable name equals and value we would like to assign to the variable.

21
00:01:41,500 --> 00:01:43,990
And finally, a semicolon to the end of the line.

22
00:01:44,740 --> 00:01:54,080
Or we can first declare the variable and then you type in the name and equals the value and a semicolon.

23
00:01:54,740 --> 00:01:57,130
OK, how it works in practice.

24
00:01:57,580 --> 00:01:59,760
I'm going to show you the second case here.

25
00:02:00,190 --> 00:02:05,560
So and enter here and number of followers.

26
00:02:06,900 --> 00:02:11,310
And intelligence offers us the variable name Anta.

27
00:02:13,290 --> 00:02:21,010
And then equals and one hundred and ninety five and a semicolon here as well.

28
00:02:21,910 --> 00:02:32,350
The other option is to define it in one line, the easiest way to do that is to delete this here and

29
00:02:32,350 --> 00:02:32,890
that's it.

30
00:02:33,710 --> 00:02:39,470
Both correct, but the second one is used one, we don't know the value of the variable at the beginning,

31
00:02:39,650 --> 00:02:41,600
but we will calculate it later.

32
00:02:42,700 --> 00:02:50,050
OK, so what data types Java has, there are two groups, primitives and object references, there are

33
00:02:50,050 --> 00:02:52,690
separate lectures to explain them in details.

34
00:02:53,020 --> 00:02:56,130
But I'm going to give you a short introduction to them here.

35
00:02:56,680 --> 00:02:58,540
So let's start with primitives.

36
00:02:59,230 --> 00:03:03,880
Hole number data types are Boit, short end and long.

37
00:03:04,660 --> 00:03:11,320
They are very based on how big number they can store in here is bold because it is the default data

38
00:03:11,320 --> 00:03:12,760
type of whole numbers.

39
00:03:13,390 --> 00:03:20,320
They can be used to store whole numbers like number of players on the field or number of passengers.

40
00:03:21,160 --> 00:03:23,670
The next group is floating point numbers.

41
00:03:24,280 --> 00:03:28,090
There are two types float and double here.

42
00:03:28,090 --> 00:03:29,610
Double is the default value.

43
00:03:30,340 --> 00:03:34,840
They also vary based on how big and precise numbers they can store.

44
00:03:35,530 --> 00:03:40,320
They can be used to store bank account balance or transaction amount.

45
00:03:41,290 --> 00:03:46,600
The next group has only one type boolean which can have two states.

46
00:03:46,600 --> 00:03:54,670
True or false, it is a simple one and a good option to store values like Willett's now tomorrow, true

47
00:03:54,670 --> 00:04:00,520
or false, and the last one which can be used to store one single character char.

48
00:04:01,180 --> 00:04:07,480
It can be used for storing the energy efficiency category of a refrigerator or washing machine.

49
00:04:08,860 --> 00:04:11,690
OK, now let's move on to object references.

50
00:04:12,400 --> 00:04:18,430
They are a bit different from the primitives I mentioned in the introduction section that Objects has

51
00:04:18,430 --> 00:04:22,240
a state or states and also have behaviors.

52
00:04:22,630 --> 00:04:26,710
Primitives doesn't have that kind of functionality that objects has.

53
00:04:27,220 --> 00:04:33,000
There are many object reference types and primitives has that object reference versions as well.

54
00:04:33,460 --> 00:04:38,190
So whole numbers, byte short, integer and long.

55
00:04:38,710 --> 00:04:45,700
They are almost the same, except that they are all start with uppercase and instead of end here we

56
00:04:45,700 --> 00:04:54,160
have integer uppercase here shows that these types are object reference types and you will see all object

57
00:04:54,160 --> 00:04:56,680
types start with an uppercase.

58
00:04:57,280 --> 00:05:00,990
OK, now let's move on to floating point numbers float and double.

59
00:05:01,450 --> 00:05:02,590
Nothing special here.

60
00:05:03,310 --> 00:05:06,710
Also, Boolean has its object reference version as well.

61
00:05:07,540 --> 00:05:11,860
What is new here is the text types instead of char.

62
00:05:12,100 --> 00:05:20,680
We have a character with uppercase which can do the same thing for a single character and a new data

63
00:05:20,680 --> 00:05:26,290
type string string can store almost unlimited amount of text.

64
00:05:26,740 --> 00:05:33,160
It can be used to store sentences, descriptions, titles, basically any kind of text.

65
00:05:33,880 --> 00:05:38,110
The last group here is the built in and custom object references.

66
00:05:38,590 --> 00:05:46,060
It can be a five right, which can be used to modify a file or system that we used in the first Java

67
00:05:46,060 --> 00:05:53,650
program lecture that blue ware can be the name of a custom object in a game or an ATM machine for a

68
00:05:53,650 --> 00:05:54,700
banking system.

69
00:05:55,360 --> 00:06:00,940
So besides these inbuilt object reference data types, we can define our custom ones as well.

70
00:06:01,810 --> 00:06:07,990
In the upcoming videos, I'm going to show you how to use primitives, how to use object references

71
00:06:08,170 --> 00:06:11,920
and how to define and use your own custom versions.

72
00:06:12,430 --> 00:06:17,230
But before that, I would like to tell you more about the naming conventions of variables.

73
00:06:17,800 --> 00:06:19,800
So variables are case sensitive.

74
00:06:20,200 --> 00:06:26,170
For example, if you would like to use a variable, you need to type in exactly the same name Binya

75
00:06:26,170 --> 00:06:26,920
declared it.

76
00:06:27,460 --> 00:06:33,790
The next one is that typically variables cannot be declared two times with the same name in the same

77
00:06:33,790 --> 00:06:35,830
class or in the same method.

78
00:06:36,310 --> 00:06:43,540
Also, variable name must start with a letter or dollar mark or underscore, but I don't recommend you

79
00:06:43,540 --> 00:06:46,030
the last two after the first letter.

80
00:06:46,120 --> 00:06:49,750
It can contain numbers, but it isn't recommended either.

81
00:06:50,020 --> 00:06:54,930
And last here, variable names cannot be equal to reserved keywords of Java.

82
00:06:55,660 --> 00:07:04,510
Here you can see a list of the reserved keywords abstract continue for new switch and the list goes

83
00:07:04,510 --> 00:07:04,770
on.

84
00:07:05,410 --> 00:07:07,450
You don't need to memorize these Java.

85
00:07:07,450 --> 00:07:11,440
We warn you that you cannot use these words as variable names.

86
00:07:11,980 --> 00:07:17,500
You might think this list is very long, but don't worry, I will explain all of them later in the course.

87
00:07:18,160 --> 00:07:22,390
One last thing I would like to share with you is the naming standards and business.

88
00:07:23,110 --> 00:07:27,520
These are not forced by Java and it is not necessary to follow them.

89
00:07:27,820 --> 00:07:31,180
But they can make your code more readable if you stick to them.

90
00:07:31,510 --> 00:07:38,260
Also, if you apply for a job and you apply these recommendations, it will show the interviewers that

91
00:07:38,260 --> 00:07:41,230
you are familiar with the business naming conventions.

92
00:07:41,750 --> 00:07:43,960
The first point is Camil case.

93
00:07:44,470 --> 00:07:51,970
So the variable names first word should start with lowercase and every other word in the variable name

94
00:07:52,210 --> 00:07:57,640
should start with uppercase, like I did with number of followers.

95
00:07:58,090 --> 00:08:02,110
No lower case than of with uppercase and follower's.

96
00:08:02,110 --> 00:08:03,280
With uppercase to.

97
00:08:04,240 --> 00:08:09,410
The next one is that the variable names should fully describe what the variable contains.

98
00:08:09,670 --> 00:08:17,500
So don't name the variables like X, Y, Z or A or B or C instead is meaningful names.

99
00:08:18,160 --> 00:08:24,820
If you go back to your code a week later, you will hardly remember what A or B or C means.

100
00:08:25,750 --> 00:08:32,680
The following point is that do not use abbreviations if you can avoid them, use long variable names

101
00:08:32,680 --> 00:08:33,310
instead.

102
00:08:33,970 --> 00:08:39,490
OK, the next recommendation is that do not reduce the variable names for other purposes.

103
00:08:40,120 --> 00:08:46,210
For example, do not use the number of followers variable to store number of notifications.

104
00:08:46,630 --> 00:08:49,240
Create another variable for that instead.

105
00:08:50,080 --> 00:08:56,390
And the last one I mentioned before, do not use Tollerson or underscore in the variable names.

106
00:08:57,260 --> 00:08:59,470
OK, that's pretty much it.

107
00:08:59,980 --> 00:09:01,330
See you in the next video.

108
00:09:01,330 --> 00:09:03,550
But I will tell you more about primitives.