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These are the user uploaded subtitles that are being translated: 1 1 00:00:01,430 --> 00:00:04,900 In the last lecture we implemented a new class 2 2 00:00:04,900 --> 00:00:09,660 which showed us the need for encapsulation and data privacy. 3 3 00:00:09,660 --> 00:00:13,330 So let's now tackle this very important principle 4 4 00:00:13,330 --> 00:00:15,313 of object oriented programming. 5 5 00:00:17,150 --> 00:00:21,350 Now first, remember that encapsulation basically means 6 6 00:00:21,350 --> 00:00:25,990 to keep some properties and methods private inside the class 7 7 00:00:25,990 --> 00:00:30,500 so that they are not accessible from outside of the class. 8 8 00:00:30,500 --> 00:00:34,110 Then the rest of the methods are basically exposed 9 9 00:00:34,110 --> 00:00:38,530 as a public interface, which we can also call API. 10 10 00:00:38,530 --> 00:00:41,380 So this is essential to do in anything 11 11 00:00:41,380 --> 00:00:44,000 more than a toy application. 12 12 00:00:44,000 --> 00:00:47,930 Now, there are two big reasons why we need encapsulation 13 13 00:00:47,930 --> 00:00:49,650 and data privacy. 14 14 00:00:49,650 --> 00:00:52,290 So first it is to prevent code 15 15 00:00:52,290 --> 00:00:56,070 from outside of a class to accidentally manipulate 16 16 00:00:56,070 --> 00:00:58,740 or data inside the class. 17 17 00:00:58,740 --> 00:01:00,570 And that's exactly what we did 18 18 00:01:00,570 --> 00:01:03,680 by the end of the last lecture here. 19 19 00:01:03,680 --> 00:01:05,310 So this is also the reason why 20 20 00:01:05,310 --> 00:01:08,080 we implement a public interface. 21 21 00:01:08,080 --> 00:01:12,070 So we are not supposed to manually mess with this property 22 22 00:01:12,070 --> 00:01:14,203 and therefore we should encapsulate it. 23 23 00:01:15,140 --> 00:01:16,460 Now, the second reason is 24 24 00:01:16,460 --> 00:01:20,000 that when we expose only a small interface 25 25 00:01:20,000 --> 00:01:24,920 so a small API consisting only of a few public methods 26 26 00:01:24,920 --> 00:01:28,250 then we can change all the other internal methods 27 27 00:01:28,250 --> 00:01:29,820 with more confidence. 28 28 00:01:29,820 --> 00:01:32,240 Because in this case, we can be sure 29 29 00:01:32,240 --> 00:01:36,910 that external code does not rely on these private methods. 30 30 00:01:36,910 --> 00:01:39,750 And so therefore our code will not break 31 31 00:01:39,750 --> 00:01:42,110 when we do internal changes. 32 32 00:01:42,110 --> 00:01:43,930 So that's what encapsulation 33 33 00:01:43,930 --> 00:01:47,290 and data privacy are and the reasons for it. 34 34 00:01:47,290 --> 00:01:49,493 And so let's now actually implement it. 35 35 00:01:50,350 --> 00:01:52,940 However JavaScript classes actually 36 36 00:01:52,940 --> 00:01:57,740 do not yet support real data privacy and encapsulation. 37 37 00:01:57,740 --> 00:02:01,740 Now there is a proposal to add truly private class fields 38 38 00:02:01,740 --> 00:02:03,800 and methods to the language, 39 39 00:02:03,800 --> 00:02:06,300 but it's not completely ready yet. 40 40 00:02:06,300 --> 00:02:09,020 I will still show it to you in the next lecture 41 41 00:02:09,020 --> 00:02:10,800 because it's really cool 42 42 00:02:10,800 --> 00:02:13,940 but even when this feature ships in the browser 43 43 00:02:13,940 --> 00:02:17,870 it will take some time until you can use it with confidence. 44 44 00:02:17,870 --> 00:02:22,400 And so in this lecture, we will basically fake encapsulation 45 45 00:02:22,400 --> 00:02:25,460 by simply using a convention. 46 46 00:02:25,460 --> 00:02:29,220 So the first candidate to protect here is again, 47 47 00:02:29,220 --> 00:02:32,930 this movements array that we have been talking about. 48 48 00:02:32,930 --> 00:02:35,600 So the movements are mission critical data 49 49 00:02:35,600 --> 00:02:38,180 and so here we will protect this data 50 50 00:02:38,180 --> 00:02:40,913 so that no one can accidentally manipulate it. 51 51 00:02:41,840 --> 00:02:45,700 And for now, all we will do is to add this underscore 52 52 00:02:45,700 --> 00:02:49,353 in front of the property name and that's it. 53 53 00:02:50,350 --> 00:02:53,373 Now we need to then go ahead and change it everywhere. 54 54 00:02:54,770 --> 00:02:59,770 So that's here and yeah, that's actually it. 55 55 00:03:00,020 --> 00:03:03,290 So again this does not actually make 56 56 00:03:03,290 --> 00:03:05,570 the property truly private 57 57 00:03:05,570 --> 00:03:08,430 because this is just a convention. 58 58 00:03:08,430 --> 00:03:12,180 So it's something that developers agree to use 59 59 00:03:12,180 --> 00:03:14,910 and then everyone does it this way. 60 60 00:03:14,910 --> 00:03:19,910 But since it is not truly private we call this protected, 61 61 00:03:21,390 --> 00:03:24,683 so protected property. 62 62 00:03:26,630 --> 00:03:31,470 And so now if we wanted to get the movements outside here 63 63 00:03:31,470 --> 00:03:34,220 we could, of course still do this. 64 64 00:03:34,220 --> 00:03:36,040 So that's what I was just saying 65 65 00:03:37,210 --> 00:03:42,170 which is that the data here is of course still accessible 66 66 00:03:42,170 --> 00:03:46,750 if we use this underscore outside here as well 67 67 00:03:46,750 --> 00:03:49,230 but at least now everyone on your team 68 68 00:03:49,230 --> 00:03:52,730 and that includes yourself will know that this property 69 69 00:03:52,730 --> 00:03:56,900 is not supposed to be touched outside of the class. 70 70 00:03:56,900 --> 00:03:58,520 So you can still do it 71 71 00:03:58,520 --> 00:04:02,173 but at least you will know that it is wrong, okay? 72 72 00:04:03,110 --> 00:04:06,040 Now, if we still wanted to give access 73 73 00:04:06,040 --> 00:04:08,850 to the movements array from the outside 74 74 00:04:08,850 --> 00:04:12,573 then we would have to implement a public method for that. 75 75 00:04:13,920 --> 00:04:16,033 So let's do that actually right here. 76 76 00:04:17,060 --> 00:04:20,930 So let's say get movements. 77 77 00:04:20,930 --> 00:04:24,240 And of course we could also create a getter here 78 78 00:04:24,240 --> 00:04:28,730 instead of this method, but let's just keep it simple. 79 79 00:04:28,730 --> 00:04:31,610 So it's very common to actually have a method 80 80 00:04:31,610 --> 00:04:36,200 that is called get or set instead of using a real getter 81 81 00:04:36,200 --> 00:04:37,183 or a real setter. 82 82 00:04:38,480 --> 00:04:40,030 And so all that this will do 83 83 00:04:40,030 --> 00:04:44,603 is to return this.movements. 84 84 00:04:45,870 --> 00:04:47,480 And so now this would be 85 85 00:04:47,480 --> 00:04:52,480 the correct way to get the movements, so get movements. 86 86 00:04:57,150 --> 00:04:59,060 And so this one everyone 87 87 00:04:59,060 --> 00:05:01,740 can still at least access the movements 88 88 00:05:01,740 --> 00:05:03,970 but they cannot override them. 89 89 00:05:03,970 --> 00:05:06,550 So they cannot set the movements 90 90 00:05:06,550 --> 00:05:11,190 unless of course they use the underscore with the convention 91 91 00:05:11,190 --> 00:05:12,500 but then at least they will know 92 92 00:05:12,500 --> 00:05:15,500 that it's wrong to access the property. 93 93 00:05:15,500 --> 00:05:19,923 Next, we could also protect here the pin. 94 94 00:05:21,060 --> 00:05:24,160 So this is also something that doesn't make much sense 95 95 00:05:24,160 --> 00:05:26,980 to be accessible from the outside. 96 96 00:05:26,980 --> 00:05:29,917 And in fact, we could make everything protected here 97 97 00:05:29,917 --> 00:05:34,040 but I think that like this, we are good to go. 98 98 00:05:34,040 --> 00:05:36,800 So this is just a small example anyway. 99 99 00:05:36,800 --> 00:05:39,173 And so for now, let's leave it like this. 100 100 00:05:40,090 --> 00:05:42,950 To finish, let's just also protect 101 101 00:05:42,950 --> 00:05:46,140 then the approved loan method. 102 102 00:05:46,140 --> 00:05:48,650 So this one I also mentioned by the end 103 103 00:05:48,650 --> 00:05:50,750 of the previous lecture. 104 104 00:05:50,750 --> 00:05:53,410 So this is a method that is only 105 105 00:05:53,410 --> 00:05:56,400 supposed to be internally by the bank. 106 106 00:05:56,400 --> 00:05:58,920 Let's say basically just to check 107 107 00:05:58,920 --> 00:06:01,200 if a loan should be approved. 108 108 00:06:01,200 --> 00:06:04,630 So essentially this method here should not be part 109 109 00:06:04,630 --> 00:06:08,653 of the public API, but all the others should be. 110 110 00:06:09,660 --> 00:06:11,890 So right now we are protecting this method. 111 111 00:06:11,890 --> 00:06:14,960 And so our public API right now consists 112 112 00:06:14,960 --> 00:06:18,823 of these other four remaining methods, all right? 113 113 00:06:20,160 --> 00:06:24,730 So this is how we protect fields from unwanted access. 114 114 00:06:24,730 --> 00:06:27,860 Now, as I said, of course, developers need to know 115 115 00:06:27,860 --> 00:06:31,090 about this convention and need to follow it 116 116 00:06:31,090 --> 00:06:34,940 because otherwise everything will still be public. 117 117 00:06:34,940 --> 00:06:37,800 But now in the next lecture, we're actually gonna talk 118 118 00:06:37,800 --> 00:06:41,500 about truly private fields and methods. 119 119 00:06:41,500 --> 00:06:45,163 And so with that, we will then fix this problem for good. 10564