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These are the user uploaded subtitles that are being translated: 1 1 00:00:05,270 --> 00:00:07,410 Okay, I thought I'd do a brief video 2 2 00:00:07,410 --> 00:00:10,210 on abstract data types because lists 3 3 00:00:10,210 --> 00:00:12,110 is the first abstract data type 4 4 00:00:12,110 --> 00:00:14,450 we're going to look at in the course. 5 5 00:00:14,450 --> 00:00:18,970 So an abstract data type isn't a concrete data structure 6 6 00:00:18,970 --> 00:00:20,890 in the sense that an array is. 7 7 00:00:20,890 --> 00:00:24,020 It doesn't dictate how the data is organised. 8 8 00:00:24,020 --> 00:00:27,150 With arrays, we know that we have to store 9 9 00:00:27,150 --> 00:00:29,460 all the items as one contiguous blah 10 10 00:00:29,460 --> 00:00:32,260 and arrays also dictate that every item in the array 11 11 00:00:32,260 --> 00:00:34,480 has to occupy the same amount of memory. 12 12 00:00:34,480 --> 00:00:37,690 So arrays are telling us how the data has to be stored 13 13 00:00:37,690 --> 00:00:39,350 but lists don't do that. 14 14 00:00:39,350 --> 00:00:42,530 Lists are more of a conceptual idea 15 15 00:00:42,530 --> 00:00:47,520 and they dictate the operations we can perform 16 16 00:00:47,520 --> 00:00:50,690 on the data set, not the items themselves. 17 17 00:00:50,690 --> 00:00:52,650 An abstract data type doesn't do something 18 18 00:00:52,650 --> 00:00:55,383 like say you can only multiply these items together, 19 19 00:00:55,383 --> 00:00:59,230 it's more that it dictates how we can access the items. 20 20 00:00:59,230 --> 00:01:01,370 Can we do random access? 21 21 00:01:01,370 --> 00:01:04,210 Can we get to the first item that we added? 22 22 00:01:04,210 --> 00:01:06,510 Can we get to the last item that we added? 23 23 00:01:06,510 --> 00:01:10,980 And so, an abstract data type is more about behaviour 24 24 00:01:10,980 --> 00:01:12,850 and what operations you can do. 25 25 00:01:12,850 --> 00:01:16,670 Now in Java, a concrete data structure like an array 26 26 00:01:16,670 --> 00:01:18,840 is usually a class. 27 27 00:01:18,840 --> 00:01:21,250 Arrays might actually be an exception to that. 28 28 00:01:21,250 --> 00:01:23,180 So you'll see as we go through the course 29 29 00:01:23,180 --> 00:01:25,180 and we look at other concrete data structures, 30 30 00:01:25,180 --> 00:01:27,710 there's usually a class for them in the JDK. 31 31 00:01:27,710 --> 00:01:29,658 When it comes to an abstract data type, 32 32 00:01:29,658 --> 00:01:33,574 normally those are interfaces, which makes sense right? 33 33 00:01:33,574 --> 00:01:36,260 Because they're not telling you how to store the data, 34 34 00:01:36,260 --> 00:01:39,270 they're specifying behaviour and that's 35 35 00:01:39,270 --> 00:01:41,100 commonly done with an interface. 36 36 00:01:41,100 --> 00:01:45,530 And so basically, any data structure can be used 37 37 00:01:45,530 --> 00:01:47,730 to implement an abstract data type, 38 38 00:01:47,730 --> 00:01:51,050 as long as you have a class that implements the interface 39 39 00:01:51,050 --> 00:01:52,830 for the abstract data type, 40 40 00:01:52,830 --> 00:01:56,800 any class can behave like that abstract data type. 41 41 00:01:56,800 --> 00:02:00,380 So in the case of lists, any class that implements 42 42 00:02:00,380 --> 00:02:02,550 the list interface, is a list 43 43 00:02:02,550 --> 00:02:04,880 and so you could have a class that uses 44 44 00:02:04,880 --> 00:02:06,690 an array for the list. 45 45 00:02:06,690 --> 00:02:08,870 If that class implements the list interface, 46 46 00:02:08,870 --> 00:02:10,510 it can be treated like a list. 47 47 00:02:10,510 --> 00:02:11,620 You could have a class, 48 48 00:02:11,620 --> 00:02:13,070 this would be a terrible thing to do, 49 49 00:02:13,070 --> 00:02:16,100 but you could have a class that has individual fields 50 50 00:02:16,100 --> 00:02:17,650 for every item in the list. 51 51 00:02:17,650 --> 00:02:21,280 As long as that class implements the list interface, 52 52 00:02:21,280 --> 00:02:22,113 it's a list. 53 53 00:02:22,113 --> 00:02:23,700 You can treat it like a list. 54 54 00:02:23,700 --> 00:02:26,100 And so when it comes to an abstract data type, 55 55 00:02:26,100 --> 00:02:28,410 they're not concrete data structures, 56 56 00:02:28,410 --> 00:02:30,970 they don't dictate how the data can be stored, 57 57 00:02:30,970 --> 00:02:34,159 but they do dictate the operations you can do 58 58 00:02:34,159 --> 00:02:36,580 on the abstract data type. 59 59 00:02:36,580 --> 00:02:39,540 So for example with lists, let's say you can add an item, 60 60 00:02:39,540 --> 00:02:40,700 you can remove an item, 61 61 00:02:40,700 --> 00:02:42,692 you can get the index of an item, et. Cetera, 62 62 00:02:42,692 --> 00:02:45,080 but they don't say and this is the way 63 63 00:02:45,080 --> 00:02:47,020 you have to store the items in the list. 64 64 00:02:47,020 --> 00:02:48,080 They don't say that. 65 65 00:02:48,080 --> 00:02:51,080 So now that we have some idea what an abstract dat type is, 66 66 00:02:51,080 --> 00:02:54,950 let's move on to looking at list in the JDK. 67 67 00:02:54,950 --> 00:02:56,500 I'll see you in the next video. 5817