1 00:00:01,060 --> 00:00:07,770 Let's not look at information hiding which is an important design principle that helps in building badly 2 00:00:07,770 --> 00:00:15,800 design software as mentioned earlier we'll be using access modifiers to achieve information hiding Joshua 3 00:00:15,820 --> 00:00:21,820 Bloch mentions in one of the items that we must strive to write good programs rather than fast ones 4 00:00:21,830 --> 00:00:22,200 . 5 00:00:22,630 --> 00:00:28,570 And if a good program is not fast enough then its underlying design principles will allow the program 6 00:00:28,570 --> 00:00:30,070 to be optimized later. 7 00:00:30,920 --> 00:00:35,010 So it is important to learn and use good design principles. 8 00:00:35,030 --> 00:00:38,140 So let's go ahead and learn about information Heidi. 9 00:00:38,570 --> 00:00:46,380 We'll be discussing a couple of important effective July items to understand this topic Harmatz understand 10 00:00:46,380 --> 00:00:54,550 what encapsulation is encapsulation is basically a language facility that allows bundling of data and 11 00:00:54,550 --> 00:00:59,630 methods that operate on that data in July we already know how to do this. 12 00:00:59,720 --> 00:01:01,160 It is basically done using it. 13 00:01:01,160 --> 00:01:03,540 Class class has methods. 14 00:01:03,710 --> 00:01:09,160 Andi does nothing but Grilli of on here is an example. 15 00:01:09,410 --> 00:01:16,250 It is our familiar student class which bundles Littlefield's and run Metford operating on one of the 16 00:01:16,250 --> 00:01:23,480 read affiance only addition here is that public access modifier has been added to the class variables 17 00:01:23,630 --> 00:01:30,980 and the method encapsulation is one of the core features of object oriented programming. 18 00:01:31,050 --> 00:01:35,520 However it alone does not lead to good software design. 19 00:01:35,700 --> 00:01:43,260 To follow additional design principles to make that happen and we will look at a couple of them let's 20 00:01:43,260 --> 00:01:46,380 reconsider our student class example here. 21 00:01:46,410 --> 00:01:48,930 All variables are declared as public. 22 00:01:49,020 --> 00:01:56,170 That means that part of the API on any kind called can access them directly that is your internal Dauphin's 23 00:01:56,190 --> 00:02:03,090 are exposed and it is a bad design as it leads to something called tight coupling that is client code 24 00:02:03,180 --> 00:02:09,920 is tightly coupled to your program let's consider the Ginnifer in this example and let's try to understand 25 00:02:10,100 --> 00:02:12,410 what issues we can how do you get by coupling 26 00:02:15,590 --> 00:02:18,950 one issue is we cannot enforce invariants. 27 00:02:19,250 --> 00:02:25,890 That is we cannot define a fixed value range of values for the variable for example for the gender field 28 00:02:26,130 --> 00:02:32,820 there is no way we can restrict gender to only these three values male female and transgender since 29 00:02:32,820 --> 00:02:39,500 grindcore can directly accident or field they can assign it any value they wish that is any value out 30 00:02:39,660 --> 00:02:44,140 of this range and that could bring the system into an incorrect state. 31 00:02:45,010 --> 00:02:51,400 In fact if you recall our Dymov student class example V-1 Axelson gender free directly from the student 32 00:02:51,400 --> 00:02:54,730 best class in order to set a value. 33 00:02:54,760 --> 00:02:59,980 Did everyone do your demo very will change this based on the information hiding principle that we are 34 00:02:59,980 --> 00:03:07,630 going to learn in this lesson and that if you could with that they cannot change the internal data representation 35 00:03:07,830 --> 00:03:09,670 without effort being blind scored. 36 00:03:10,680 --> 00:03:17,740 In our example gender is of type String undef Evista converted to and then the client code would also 37 00:03:17,740 --> 00:03:23,820 have to change the date or type from strength and uming it uses the gender directly. 38 00:03:24,100 --> 00:03:25,400 That's not a good thing. 39 00:03:25,510 --> 00:03:28,980 Ask clansmen not expect the API to change in this way. 40 00:03:29,870 --> 00:03:32,600 That is once that all that gender is off by a string. 41 00:03:32,780 --> 00:03:34,010 And this public. 42 00:03:34,220 --> 00:03:36,430 Which means that it is part of the API. 43 00:03:36,740 --> 00:03:42,610 Then they would expect it to remain as string for whatever so these are a couple of issues. 44 00:03:42,780 --> 00:03:47,860 Coupling And this brings us to an advice from effective Java. 45 00:03:47,910 --> 00:03:57,270 Item 14 which is in public grassers use accessor methods are not public views and this is a most fundamental 46 00:03:57,270 --> 00:03:59,230 rule of information hiding. 47 00:03:59,430 --> 00:04:06,990 Let's see what accessor methods are and how we can use them to improve or worse during class and this 48 00:04:06,990 --> 00:04:13,920 illustration only changes to a general election for wonderful access modifier is change from public 49 00:04:13,920 --> 00:04:15,040 to private. 50 00:04:15,300 --> 00:04:20,080 And then we introduce two methods one public sector matter and one public get on better. 51 00:04:20,300 --> 00:04:26,820 So that matter is used to initialize large underfeed the get method simply reduce the value of the Jennifer 52 00:04:27,990 --> 00:04:34,020 not that a sitter is also referred to as a mutator as we are basically mutating the state. 53 00:04:34,300 --> 00:04:39,640 Again it is also referred to as an accessor which is what the effective delightsome that we just saw 54 00:04:39,740 --> 00:04:44,560 refers to so this is how you should initialize instance fees. 55 00:04:44,740 --> 00:04:52,880 So it does change the client code can no longer access the gender field directly in item 14 Joshua Bloch 56 00:04:52,880 --> 00:04:59,290 also mentions about a couple of core classes in the standard July API that violated this principle. 57 00:04:59,720 --> 00:05:03,840 And unfortunately that led to serious performance issues which are still there. 58 00:05:04,670 --> 00:05:10,210 Probably they could not fix those issues because the code is already being widely used. 59 00:05:10,310 --> 00:05:14,330 That is if they change their design it would break the code in scored. 60 00:05:14,810 --> 00:05:21,080 In fact ideas like Eclipse provide you the option to automatically insert getters and setters if you 61 00:05:21,080 --> 00:05:25,180 declare private instance feels that we actually show this to you. 62 00:05:25,190 --> 00:05:32,630 In my Eclipse ID OK this is my Eclipse and this is a class that I how. 63 00:05:32,700 --> 00:05:42,420 Let me just add a private instance when I read it is a type an ID as you can see Eclipse's highlighting 64 00:05:42,420 --> 00:05:43,590 this idea. 65 00:05:43,950 --> 00:05:45,450 And when I holler over it. 66 00:05:45,450 --> 00:05:51,860 It says I feel is not used and it gives me three quick fixes on one of them is create. 67 00:05:51,870 --> 00:05:53,760 Get an answer for ID. 68 00:05:53,790 --> 00:05:55,660 Let's talk about it about the other two options. 69 00:05:55,720 --> 00:06:03,260 Click on Doc and it gives me an option via like an ad these are get done on centers. 70 00:06:03,300 --> 00:06:05,920 So let me just say asfast matter. 71 00:06:06,460 --> 00:06:07,380 And here it is. 72 00:06:07,380 --> 00:06:11,490 So you the getters and setters have been added automatically. 73 00:06:11,490 --> 00:06:13,850 So let me just remove them. 74 00:06:14,220 --> 00:06:22,080 And if the idea is already declared and if it is being used from one of the metrics in the class then 75 00:06:22,080 --> 00:06:27,540 it will not be highlighted an item will not be highlighted in which case we can go here in the source 76 00:06:27,900 --> 00:06:34,500 in the menu and click on this Jondrette getters and setters over here it shows Id just click on that 77 00:06:34,520 --> 00:06:34,820 . 78 00:06:35,280 --> 00:06:43,510 And if you click OK it once again automatically creates get transmitter's So it just shows the importance 79 00:06:43,510 --> 00:06:45,020 of getters and setters. 80 00:06:45,340 --> 00:06:49,100 So even eclipse provides an option to automatically gendered them 81 00:06:51,950 --> 00:06:58,020 not see how the simple design principle addresses the two issues that we saw earlier a tight coupling 82 00:06:59,010 --> 00:07:04,800 one was about enforcing invariants while the second was about changing the internal data representation 83 00:07:04,800 --> 00:07:05,500 . 84 00:07:05,730 --> 00:07:08,260 First let's see how the invariant issue is addressed. 85 00:07:08,400 --> 00:07:15,420 And here is a modified code if you recall we wanted gender to be restricted to only three values male 86 00:07:15,480 --> 00:07:18,630 female and transgender to enforce this. 87 00:07:18,840 --> 00:07:25,140 The if statement in the setter method is checking of the input gender that is passed is one of the three 88 00:07:25,140 --> 00:07:27,210 valid gender values. 89 00:07:27,360 --> 00:07:32,640 If that's not the case then an exception is thrown indicating that an invalid gender value has been 90 00:07:32,640 --> 00:07:33,260 passed. 91 00:07:33,970 --> 00:07:39,350 Don't worry about the exceptionally good you will understand it when we get to exceptions. 92 00:07:39,390 --> 00:07:45,150 So as you can see not allowing could directly access their underfilled is permitting us to enforce an 93 00:07:45,210 --> 00:07:52,760 invariant next issue was related to changing in dinner the presentation of one or more fields without 94 00:07:52,820 --> 00:07:54,320 affecting clangor. 95 00:07:54,770 --> 00:08:00,710 For this we mentioned about changing gender from string to and let's assume that this change is necessary 96 00:08:00,740 --> 00:08:02,110 to improve performance. 97 00:08:03,210 --> 00:08:09,010 But as you can see Klein is already using certain ungraded methods and is expecting gender to remain 98 00:08:09,040 --> 00:08:09,680 Astron. 99 00:08:10,610 --> 00:08:17,060 So the TV make should not affect the signatures of these two methods that Rick Klein could will be unaffected 100 00:08:17,080 --> 00:08:17,320 . 101 00:08:18,330 --> 00:08:22,890 Since we are not following a good design principle this can be they can get off very easily. 102 00:08:24,890 --> 00:08:32,180 And here is a modified called a new private and free agent that has been introduced all underfilled 103 00:08:32,270 --> 00:08:34,940 remains as it's its subject matter. 104 00:08:35,030 --> 00:08:42,080 We'll still use string as in book but but in the subject our methods body beside the gender feel based 105 00:08:42,080 --> 00:08:49,340 on the input past have the input in the past as mail then I generally said to one if gender is female 106 00:08:49,490 --> 00:08:56,420 then gender is said to do and of gender passes transgender then I did the research to three but if gender 107 00:08:56,610 --> 00:09:03,330 is something other than these three then I gender would remain zero which is its default value and the 108 00:09:03,330 --> 00:09:10,440 method would to an exception as before gender field is also being set as it can be used and get gender 109 00:09:10,440 --> 00:09:17,450 mattered so with this change the client code is totally unaffected and they don't even know about this 110 00:09:17,510 --> 00:09:18,840 implementation change. 111 00:09:19,640 --> 00:09:24,860 So this design has given us the flexibility to change that implementation without affecting the class 112 00:09:25,930 --> 00:09:32,080 so as you can see by hiding the fields using a private modifier and by using public getters and setters 113 00:09:32,710 --> 00:09:36,070 we could address both the issues of tight coupling. 114 00:09:36,070 --> 00:09:43,570 The code is now set to be loosely coupled or decoupled as the client code now only communicates through 115 00:09:43,570 --> 00:09:48,290 the API and is oblivious to the implementation details. 116 00:09:48,340 --> 00:09:55,880 So there is no more meddling with that data if it is directly so with meaningful package structure combined 117 00:09:55,880 --> 00:10:03,510 with good information hiding principles we can double up loosely coupled components if how loosely couple 118 00:10:03,510 --> 00:10:10,610 designs we can develop best use and optimize software components in isolation. 119 00:10:11,070 --> 00:10:18,910 We just saw how student class could be optimized by converting Gandolfi from string to another advantage 120 00:10:18,910 --> 00:10:25,230 of having loosley couple competences that they can be utilized in marketable projects and they also 121 00:10:25,230 --> 00:10:30,940 decrease the risk in building large systems that is a system for which a particular component is Dola 122 00:10:31,080 --> 00:10:31,950 might fail. 123 00:10:32,490 --> 00:10:35,890 But the component itself might be useful in some other project. 124 00:10:36,920 --> 00:10:40,230 So it is important to package your classes in a meaningful way. 125 00:10:40,300 --> 00:10:47,890 Unadopt good designs that can lead to doping loosely coupled components this and this lesson here in 126 00:10:47,890 --> 00:10:54,020 the next lesson we will review another effective delightsome related information hiding it but with 127 00:10:54,020 --> 00:10:57,280 a few more suggestions on creating loosely coupled systems. 128 00:10:57,430 --> 00:10:58,170 Thank you.