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Okay, I thought I'd do a brief video 2

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on abstract data types because lists 3

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is the first abstract data type 4

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we're going to look at in the course. 5

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So an abstract data type isn't a concrete data structure 6

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in the sense that an array is. 7

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It doesn't dictate how the data is organised. 8

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With arrays, we know that we have to store 9

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all the items as one contiguous blah 10

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and arrays also dictate that every item in the array 11

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has to occupy the same amount of memory. 12

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So arrays are telling us how the data has to be stored 13

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but lists don't do that. 14

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Lists are more of a conceptual idea 15

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and they dictate the operations we can perform 16

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on the data set, not the items themselves. 17

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An abstract data type doesn't do something 18

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like say you can only multiply these items together, 19

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it's more that it dictates how we can access the items. 20

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Can we do random access? 21

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Can we get to the first item that we added? 22

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Can we get to the last item that we added? 23

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And so, an abstract data type is more about behaviour 24

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and what operations you can do. 25

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Now in Java, a concrete data structure like an array 26

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is usually a class. 27

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Arrays might actually be an exception to that. 28

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So you'll see as we go through the course 29

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and we look at other concrete data structures, 30

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there's usually a class for them in the JDK. 31

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When it comes to an abstract data type, 32

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normally those are interfaces, which makes sense right? 33

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Because they're not telling you how to store the data, 34

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they're specifying behaviour and that's 35

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commonly done with an interface. 36

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And so basically, any data structure can be used 37

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to implement an abstract data type, 38

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as long as you have a class that implements the interface 39

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for the abstract data type, 40

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any class can behave like that abstract data type. 41

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So in the case of lists, any class that implements 42

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the list interface, is a list 43

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and so you could have a class that uses 44

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an array for the list. 45

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If that class implements the list interface, 46

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it can be treated like a list. 47

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You could have a class, 48

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this would be a terrible thing to do, 49

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but you could have a class that has individual fields 50

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for every item in the list. 51

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As long as that class implements the list interface, 52

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it's a list. 53

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You can treat it like a list. 54

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And so when it comes to an abstract data type, 55

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they're not concrete data structures, 56

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they don't dictate how the data can be stored, 57

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but they do dictate the operations you can do 58

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on the abstract data type. 59

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So for example with lists, let's say you can add an item, 60

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you can remove an item, 61

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you can get the index of an item, et. Cetera, 62

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but they don't say and this is the way 63

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you have to store the items in the list. 64

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They don't say that. 65

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So now that we have some idea what an abstract dat type is, 66

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let's move on to looking at list in the JDK. 67

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I'll see you in the next video.