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These are the user uploaded subtitles that are being translated: 1 1 00:00:00,238 --> 00:00:02,821 (upbeat music) 2 2 00:00:05,230 --> 00:00:07,070 Well, this is gonna be a short video 3 3 00:00:07,070 --> 00:00:09,730 because the Vector class 4 4 00:00:09,730 --> 00:00:12,940 is essentially a thread safe ArrayList, 5 5 00:00:12,940 --> 00:00:16,010 but Vector actually came first and we're gonna take a 6 6 00:00:16,010 --> 00:00:19,560 look at the Vector Javadoc and we'll see, 7 7 00:00:19,560 --> 00:00:20,740 if we scroll down a bit 8 8 00:00:20,740 --> 00:00:23,820 that Vector has been there since the beginning. 9 9 00:00:23,820 --> 00:00:28,820 It has been in the JDK since JDK 1.0. 10 10 00:00:28,820 --> 00:00:30,920 If we come up to the top here, 11 11 00:00:30,920 --> 00:00:34,203 now, if I go back to ArrayList, 12 12 00:00:36,530 --> 00:00:38,280 so this is the ArrayList class, 13 13 00:00:38,280 --> 00:00:41,210 we'll see that that's, there was only added into 14 14 00:00:41,210 --> 00:00:45,200 the JDK in JDK version 1.2. 15 15 00:00:45,200 --> 00:00:47,940 Now, if you've been using Java as long as I have, 16 16 00:00:47,940 --> 00:00:50,780 you might remember when ArrayList was introduced. 17 17 00:00:50,780 --> 00:00:54,740 Before that, the list go-to class was Vector, 18 18 00:00:54,740 --> 00:00:59,640 and so the question is if Vector was in JDK version 1.0 19 19 00:00:59,640 --> 00:01:01,500 and it has pretty much the same methods 20 20 00:01:01,500 --> 00:01:03,490 as the ArrayList class, 21 21 00:01:03,490 --> 00:01:06,310 why was ArrayList added to the JDK? 22 22 00:01:06,310 --> 00:01:08,923 Well, the answer lies in the documentation. 23 23 00:01:09,780 --> 00:01:12,160 If we scroll back up, we'll see right here 24 24 00:01:12,160 --> 00:01:14,330 in big bold letters for ArrayList, 25 25 00:01:14,330 --> 00:01:17,940 this implementation is not synchronised, 26 26 00:01:17,940 --> 00:01:21,510 and if we go back to the Vector class, 27 27 00:01:21,510 --> 00:01:24,620 it says unlike the new collection implementations, 28 28 00:01:24,620 --> 00:01:27,310 Vector is synchronised. 29 29 00:01:27,310 --> 00:01:29,920 So Vector is thread safe meaning it's okay 30 30 00:01:29,920 --> 00:01:33,000 to use it from different threads without you having 31 31 00:01:33,000 --> 00:01:35,060 to synchronise the code. 32 32 00:01:35,060 --> 00:01:37,380 But ArrayList is not. 33 33 00:01:37,380 --> 00:01:39,670 So if you only read an ArrayList, 34 34 00:01:39,670 --> 00:01:42,180 then it's safe to use it from multiple threads, 35 35 00:01:42,180 --> 00:01:43,670 no data will be clobbered, 36 36 00:01:43,670 --> 00:01:46,350 but if you use ArrayList with multiple threads 37 37 00:01:46,350 --> 00:01:48,610 and one or more of those threads is writing 38 38 00:01:48,610 --> 00:01:50,650 to the ArrayList by adding, 39 39 00:01:50,650 --> 00:01:53,810 deleting, setting or changing objects in the list, 40 40 00:01:53,810 --> 00:01:56,630 then you could run into a conflict. 41 41 00:01:56,630 --> 00:01:58,910 You could have threading conflicts, 42 42 00:01:58,910 --> 00:02:00,070 and so in that case, you'd 43 43 00:02:00,070 --> 00:02:03,080 want to use Vector rather than ArrayList. 44 44 00:02:03,080 --> 00:02:05,420 So if you need thread safety, use Vector. 45 45 00:02:05,420 --> 00:02:06,990 If you don't, use ArrayList. 46 46 00:02:06,990 --> 00:02:09,170 Now, the reason that ArrayList came along 47 47 00:02:09,170 --> 00:02:13,350 is that synchronisation has an overhead involved. 48 48 00:02:13,350 --> 00:02:15,390 So it slows things down, 49 49 00:02:15,390 --> 00:02:18,000 and so when only the Vector class was available 50 50 00:02:18,000 --> 00:02:19,790 and Vector is synchronised, 51 51 00:02:19,790 --> 00:02:23,210 if you wanted to use a list backed by an array 52 52 00:02:23,210 --> 00:02:25,270 and you wanted to use the class in the JDK, 53 53 00:02:25,270 --> 00:02:26,420 you were pretty much forced 54 54 00:02:26,420 --> 00:02:28,620 to use a synchronised class even 55 55 00:02:28,620 --> 00:02:31,270 if you didn't need synchronisation, 56 56 00:02:31,270 --> 00:02:33,300 and so because of that, 57 57 00:02:33,300 --> 00:02:35,450 ArrayList was eventually added to the JDK, 58 58 00:02:35,450 --> 00:02:37,750 so that if you don't need synchronisation, 59 59 00:02:37,750 --> 00:02:39,640 you would have a class backed by an array 60 60 00:02:39,640 --> 00:02:41,510 that you could use that doesn't 61 61 00:02:41,510 --> 00:02:44,580 have the overhead involved with synchronisation, 62 62 00:02:44,580 --> 00:02:46,560 and so that's why ArrayList came along. 63 63 00:02:46,560 --> 00:02:48,860 It was because developers were saying, 64 64 00:02:48,860 --> 00:02:52,140 hey, we like Vector, but what do we do 65 65 00:02:52,140 --> 00:02:53,670 if we don't need synchronisation? 66 66 00:02:53,670 --> 00:02:55,630 We don't want the overhead associated with it, 67 67 00:02:55,630 --> 00:02:58,840 and so a couple of versions later, ArrayList came along. 68 68 00:02:58,840 --> 00:03:01,920 And so here you'll see that the documentation 69 69 00:03:01,920 --> 00:03:04,080 for ArrayList itself says 70 70 00:03:04,080 --> 00:03:06,640 if a thread safe implementation is not needed, 71 71 00:03:06,640 --> 00:03:09,610 it is recommended to use ArrayList. 72 72 00:03:09,610 --> 00:03:12,100 So you only want to use the Vector class 73 73 00:03:12,100 --> 00:03:14,660 if you need synchronisation. 74 74 00:03:14,660 --> 00:03:17,270 If you don't need it and you use the Vector class, 75 75 00:03:17,270 --> 00:03:19,660 you're going to be using a slower implementation 76 76 00:03:19,660 --> 00:03:22,120 for no reason, and that's why you 77 77 00:03:22,120 --> 00:03:24,940 want to use ArrayList unless you need 78 78 00:03:24,940 --> 00:03:27,070 a thread safe implementation. 79 79 00:03:27,070 --> 00:03:28,480 So if you need thread safety, 80 80 00:03:28,480 --> 00:03:31,870 use Vector, if you don't, use ArrayList. 81 81 00:03:31,870 --> 00:03:34,410 Okay, so let's say we do want to use Vector. 82 82 00:03:34,410 --> 00:03:36,600 Well, Vector is backed by an array just 83 83 00:03:36,600 --> 00:03:41,363 like ArrayList is and so let's go back to the IDE now. 84 84 00:03:44,870 --> 00:03:46,580 And I've created a project 85 85 00:03:46,580 --> 00:03:49,290 and I've added the same Employee class we had 86 86 00:03:49,290 --> 00:03:51,690 in the ArrayList video, 87 87 00:03:51,690 --> 00:03:53,360 same fields, same everything, 88 88 00:03:53,360 --> 00:03:54,520 I basically just copied 89 89 00:03:54,520 --> 00:03:56,200 and pasted it from that project. 90 90 00:03:56,200 --> 00:03:59,030 And right now I have this using an ArrayList. 91 91 00:03:59,030 --> 00:04:00,700 Now, if you want to use Vector, 92 92 00:04:00,700 --> 00:04:02,990 because we are assigning 93 93 00:04:02,990 --> 00:04:06,430 this into a list Employee instance rather 94 94 00:04:06,430 --> 00:04:07,890 than ArrayList Employee, 95 95 00:04:07,890 --> 00:04:10,713 all we have to do is change this to Vector, 96 96 00:04:12,900 --> 00:04:15,230 because Vector also implements list 97 97 00:04:15,230 --> 00:04:18,310 and so that's why rather than using 98 98 00:04:18,310 --> 00:04:21,670 a specific implementation in the declaration, 99 99 00:04:21,670 --> 00:04:24,370 it's always better to use the interface 100 100 00:04:24,370 --> 00:04:27,010 that the implementation is using 101 101 00:04:27,010 --> 00:04:30,380 because then you can switch out to another class 102 102 00:04:30,380 --> 00:04:32,160 that implements the same interface 103 103 00:04:32,160 --> 00:04:34,000 without having to change any code. 104 104 00:04:34,000 --> 00:04:37,600 So let's take a look at the Vector constructor. 105 105 00:04:37,600 --> 00:04:41,680 Let's go to the declaration, and let's go to this. 106 106 00:04:41,680 --> 00:04:43,870 We'll have to follow this down until we finally get 107 107 00:04:43,870 --> 00:04:46,980 to the actual code where it's doing the work. 108 108 00:04:46,980 --> 00:04:48,063 We'll keep going. 109 109 00:04:52,150 --> 00:04:56,030 And here we are and we'll see that an array is created. 110 110 00:04:56,030 --> 00:05:00,980 So it's using backing array just like ArrayList is. 111 111 00:05:00,980 --> 00:05:03,460 If we go back to Main now and we take a 112 112 00:05:03,460 --> 00:05:06,953 look at the implementation of add, 113 113 00:05:11,490 --> 00:05:16,490 and this time I want it for Vector, there you go. 114 114 00:05:17,180 --> 00:05:20,200 It's synchronised, and so 115 115 00:05:20,200 --> 00:05:24,200 that's the difference between the add method for ArrayList 116 116 00:05:24,200 --> 00:05:25,760 and the add method for Vector. 117 117 00:05:25,760 --> 00:05:28,460 Let's have a look at the ArrayList add method. 118 118 00:05:28,460 --> 00:05:30,830 I'll go to the other project, 119 119 00:05:30,830 --> 00:05:33,487 the other IntelliJ project for ArrayList. 120 120 00:05:36,800 --> 00:05:39,010 So here we are back in the project we worked with 121 121 00:05:39,010 --> 00:05:42,033 in the last video and if I go to this add method, 122 122 00:05:48,791 --> 00:05:49,624 I want the ArrayList add, 123 123 00:05:49,624 --> 00:05:52,610 we'll see that there is no synchronised keyword here, 124 124 00:05:52,610 --> 00:05:54,010 and so I want to reiterate 125 125 00:05:54,010 --> 00:05:57,080 that if you don't need thread safety, then don't use Vector. 126 126 00:05:57,080 --> 00:06:00,350 You don't want the overhead that comes with synchronisation, 127 127 00:06:00,350 --> 00:06:02,130 and if you do need thread safety, 128 128 00:06:02,130 --> 00:06:05,100 then you want to use Vector rather than using ArrayList 129 129 00:06:05,100 --> 00:06:07,790 because if you use ArrayList, 130 130 00:06:07,790 --> 00:06:10,290 then you're going to be responsible for synchronising 131 131 00:06:10,290 --> 00:06:13,890 all the calls to ArrayList methods, 132 132 00:06:13,890 --> 00:06:17,010 and so why do the work when the Vector class 133 133 00:06:17,010 --> 00:06:18,710 has already done all of that for you? 134 134 00:06:18,710 --> 00:06:19,543 And that's it. 135 135 00:06:19,543 --> 00:06:20,930 That's all I'm gonna say about Vector 136 136 00:06:20,930 --> 00:06:22,230 because it's pretty much the same 137 137 00:06:22,230 --> 00:06:24,700 as an ArrayList except that it's synchronised. 138 138 00:06:24,700 --> 00:06:27,700 The last two videos about ArrayList and Vector though, 139 139 00:06:27,700 --> 00:06:31,110 they're probably been review for some of you. 140 140 00:06:31,110 --> 00:06:32,440 I just want to make sure 141 141 00:06:32,440 --> 00:06:36,080 that we covered the two most popular classes 142 142 00:06:36,080 --> 00:06:37,580 in the JDK when it comes 143 143 00:06:37,580 --> 00:06:41,090 to just having a simple sequential list, 144 144 00:06:41,090 --> 00:06:43,810 so in the next video, we're going to move on to another type 145 145 00:06:43,810 --> 00:06:46,644 of list called a LinkedList. 146 146 00:06:46,644 --> 00:06:47,594 I'll see you there. 12512