Original subtitles

1 1

(upbeat music) 2

2

Well, this is gonna be a short video 3

3

because the Vector class 4

4

is essentially a thread safe ArrayList, 5

5

but Vector actually came first and we're gonna take a 6

6

look at the Vector Javadoc and we'll see, 7

7

if we scroll down a bit 8

8

that Vector has been there since the beginning. 9

9

It has been in the JDK since JDK 1.0. 10

10

If we come up to the top here, 11

11

now, if I go back to ArrayList, 12

12

so this is the ArrayList class, 13

13

we'll see that that's, there was only added into 14

14

the JDK in JDK version 1.2. 15

15

Now, if you've been using Java as long as I have, 16

16

you might remember when ArrayList was introduced. 17

17

Before that, the list go-to class was Vector, 18

18

and so the question is if Vector was in JDK version 1.0 19

19

and it has pretty much the same methods 20

20

as the ArrayList class, 21

21

why was ArrayList added to the JDK? 22

22

Well, the answer lies in the documentation. 23

23

If we scroll back up, we'll see right here 24

24

in big bold letters for ArrayList, 25

25

this implementation is not synchronised, 26

26

and if we go back to the Vector class, 27

27

it says unlike the new collection implementations, 28

28

Vector is synchronised. 29

29

So Vector is thread safe meaning it's okay 30

30

to use it from different threads without you having 31

31

to synchronise the code. 32

32

But ArrayList is not. 33

33

So if you only read an ArrayList, 34

34

then it's safe to use it from multiple threads, 35

35

no data will be clobbered, 36

36

but if you use ArrayList with multiple threads 37

37

and one or more of those threads is writing 38

38

to the ArrayList by adding, 39

39

deleting, setting or changing objects in the list, 40

40

then you could run into a conflict. 41

41

You could have threading conflicts, 42

42

and so in that case, you'd 43

43

want to use Vector rather than ArrayList. 44

44

So if you need thread safety, use Vector. 45

45

If you don't, use ArrayList. 46

46

Now, the reason that ArrayList came along 47

47

is that synchronisation has an overhead involved. 48

48

So it slows things down, 49

49

and so when only the Vector class was available 50

50

and Vector is synchronised, 51

51

if you wanted to use a list backed by an array 52

52

and you wanted to use the class in the JDK, 53

53

you were pretty much forced 54

54

to use a synchronised class even 55

55

if you didn't need synchronisation, 56

56

and so because of that, 57

57

ArrayList was eventually added to the JDK, 58

58

so that if you don't need synchronisation, 59

59

you would have a class backed by an array 60

60

that you could use that doesn't 61

61

have the overhead involved with synchronisation, 62

62

and so that's why ArrayList came along. 63

63

It was because developers were saying, 64

64

hey, we like Vector, but what do we do 65

65

if we don't need synchronisation? 66

66

We don't want the overhead associated with it, 67

67

and so a couple of versions later, ArrayList came along. 68

68

And so here you'll see that the documentation 69

69

for ArrayList itself says 70

70

if a thread safe implementation is not needed, 71

71

it is recommended to use ArrayList. 72

72

So you only want to use the Vector class 73

73

if you need synchronisation. 74

74

If you don't need it and you use the Vector class, 75

75

you're going to be using a slower implementation 76

76

for no reason, and that's why you 77

77

want to use ArrayList unless you need 78

78

a thread safe implementation. 79

79

So if you need thread safety, 80

80

use Vector, if you don't, use ArrayList. 81

81

Okay, so let's say we do want to use Vector. 82

82

Well, Vector is backed by an array just 83

83

like ArrayList is and so let's go back to the IDE now. 84

84

And I've created a project 85

85

and I've added the same Employee class we had 86

86

in the ArrayList video, 87

87

same fields, same everything, 88

88

I basically just copied 89

89

and pasted it from that project. 90

90

And right now I have this using an ArrayList. 91

91

Now, if you want to use Vector, 92

92

because we are assigning 93

93

this into a list Employee instance rather 94

94

than ArrayList Employee, 95

95

all we have to do is change this to Vector, 96

96

because Vector also implements list 97

97

and so that's why rather than using 98

98

a specific implementation in the declaration, 99

99

it's always better to use the interface 100

100

that the implementation is using 101

101

because then you can switch out to another class 102

102

that implements the same interface 103

103

without having to change any code. 104

104

So let's take a look at the Vector constructor. 105

105

Let's go to the declaration, and let's go to this. 106

106

We'll have to follow this down until we finally get 107

107

to the actual code where it's doing the work. 108

108

We'll keep going. 109

109

And here we are and we'll see that an array is created. 110

110

So it's using backing array just like ArrayList is. 111

111

If we go back to Main now and we take a 112

112

look at the implementation of add, 113

113

and this time I want it for Vector, there you go. 114

114

It's synchronised, and so 115

115

that's the difference between the add method for ArrayList 116

116

and the add method for Vector. 117

117

Let's have a look at the ArrayList add method. 118

118

I'll go to the other project, 119

119

the other IntelliJ project for ArrayList. 120

120

So here we are back in the project we worked with 121

121

in the last video and if I go to this add method, 122

122

I want the ArrayList add, 123

123

we'll see that there is no synchronised keyword here, 124

124

and so I want to reiterate 125

125

that if you don't need thread safety, then don't use Vector. 126

126

You don't want the overhead that comes with synchronisation, 127

127

and if you do need thread safety, 128

128

then you want to use Vector rather than using ArrayList 129

129

because if you use ArrayList, 130

130

then you're going to be responsible for synchronising 131

131

all the calls to ArrayList methods, 132

132

and so why do the work when the Vector class 133

133

has already done all of that for you? 134

134

And that's it. 135

135

That's all I'm gonna say about Vector 136

136

because it's pretty much the same 137

137

as an ArrayList except that it's synchronised. 138

138

The last two videos about ArrayList and Vector though, 139

139

they're probably been review for some of you. 140

140

I just want to make sure 141

141

that we covered the two most popular classes 142

142

in the JDK when it comes 143

143

to just having a simple sequential list, 144

144

so in the next video, we're going to move on to another type 145

145

of list called a LinkedList. 146

146

I'll see you there.