1 00:00:06,870 --> 00:00:07,920 Hi there. 2 00:00:07,920 --> 00:00:09,050 This is Day to do. 3 00:00:09,120 --> 00:00:10,620 And welcome back. 4 00:00:10,620 --> 00:00:16,050 Let's extend Tullio to add a new requirement under some interesting requirement which part still gets 5 00:00:16,690 --> 00:00:23,520 unequal to enable us to learn about another cool object oriented feature Angela and the new requirement 6 00:00:23,640 --> 00:00:30,310 is to add a new app just pockets and it would display only bookmarks which are relevant toolkits. 7 00:00:30,360 --> 00:00:36,330 For example as shown here we can have a new menu item called gets and clicking on it will display only 8 00:00:36,530 --> 00:00:38,350 kid friendly bookmarks. 9 00:00:38,370 --> 00:00:44,970 This is not that the existing system under something we plan to add in future will get some specific 10 00:00:44,970 --> 00:00:51,780 details related to the new requirement only editorial stuff like the content editors should be able 11 00:00:51,780 --> 00:00:54,240 to market bookmark as kid friendly. 12 00:00:54,630 --> 00:00:59,700 And if a bookmark is not yet approved as pet friendly then a link with the title Mark Guscott friendly 13 00:00:59,790 --> 00:01:02,090 will be disappeared with double back. 14 00:01:02,190 --> 00:01:08,760 However such a link will not be shown if the bookmark is clearly not eligible for it from Mr. dys good 15 00:01:08,760 --> 00:01:13,060 examples would be Mobius and John and horror movies. 16 00:01:13,200 --> 00:01:20,790 So basically only bookmarks that are MMOG best Cutrone show under Section no so far our class trigrams 17 00:01:21,000 --> 00:01:24,480 include different user types and their capabilities. 18 00:01:24,480 --> 00:01:29,730 Let's introduce some new classes since it is a bookmarking app and we know that will you allows us to 19 00:01:29,730 --> 00:01:32,180 bookmark LeBlanc's movies and books. 20 00:01:32,310 --> 00:01:36,100 We can have three classes representing these three different bookmark. 21 00:01:37,020 --> 00:01:43,230 And these three classes would extend the superclass called bookmark and bookmarked last defensive for 22 00:01:43,290 --> 00:01:47,960 instance variables ID title description and profile you are in. 23 00:01:48,480 --> 00:01:50,740 ID is simply the primary key of the bookmark. 24 00:01:50,760 --> 00:01:58,770 Indeed obvious so it uniquely identifies each bookmark title and description simply represent the title 25 00:01:58,770 --> 00:02:01,800 and description of the bookmark like the movie name. 26 00:02:01,830 --> 00:02:07,470 A short description of the movie profile you are in is that you want to know if the web page that has 27 00:02:07,560 --> 00:02:14,370 information that is specific with a bookmark bookmark class also defines two methods Genelec profile 28 00:02:14,370 --> 00:02:21,450 you aren't an easy kid friendly eligible mentored both of which are awarded and subprocess. 29 00:02:22,230 --> 00:02:24,750 Let's just look at what Jenrette profile you are. 30 00:02:24,750 --> 00:02:30,030 The method is responsible for let's consider this movie named into the wine. 31 00:02:30,120 --> 00:02:36,270 It's an interesting movie and for this movie the gender profile you are limited in the more B-class 32 00:02:36,810 --> 00:02:42,870 would generate this kind of a text which is assigned to the profile you already know the first part 33 00:02:42,870 --> 00:02:49,680 in the text which is the movie followed by Slash is generated by this method while for the remaining 34 00:02:49,680 --> 00:02:54,250 part the genetic profile you are on the method in the superclass is invoked. 35 00:02:54,480 --> 00:02:58,370 So it is invoked from the surplus in the browser. 36 00:02:58,380 --> 00:03:02,720 However you will see the full on and that is the text trail that I want. 37 00:03:02,790 --> 00:03:07,800 Followed by a slash which is then followed by this text generated by the generate profile you are the 38 00:03:07,800 --> 00:03:09,050 matter. 39 00:03:09,060 --> 00:03:13,970 That's because the prefix rule that I want will be automatically added by the website. 40 00:03:14,670 --> 00:03:20,500 So the Spross abortion is generating the subclass related text like the movie followed by Slash. 41 00:03:20,530 --> 00:03:27,310 Why did the super motion gender's the remaining part from the bookmarks title not fit to the general 42 00:03:27,330 --> 00:03:33,540 profile you are limited in the book plus it will generate that text book followed by Slash. 43 00:03:33,600 --> 00:03:37,760 While for the remaining text it would invoke the superclass portion. 44 00:03:38,040 --> 00:03:44,130 Next the second method is good for only eligible is responsible for deciding whether or not to display 45 00:03:44,310 --> 00:03:45,300 the link Mark. 46 00:03:45,360 --> 00:03:53,130 Ask a friendly with each bookmark so defines the base eligibility criteria to make such a decision. 47 00:03:53,130 --> 00:03:58,840 Hello bookmark class is too generic to how any specific implementation for this method. 48 00:03:58,850 --> 00:04:05,340 So implementation is supply specific on Hansis over it and for example you get friendly eligible method 49 00:04:05,350 --> 00:04:05,480 . 50 00:04:05,550 --> 00:04:12,410 In the movie class would return false if movie is off only so you can get something of the sort. 51 00:04:12,420 --> 00:04:14,600 Defined in the book márquez. 52 00:04:14,730 --> 00:04:21,120 However the method will still be present in the bookmark class as it would help in defining the contract 53 00:04:21,120 --> 00:04:29,220 for a process that is a common protocol for subprocess which is very important for polymorphism. 54 00:04:29,220 --> 00:04:35,010 Finally you can also see some instance variables that are specific to the classes book on movie and 55 00:04:35,010 --> 00:04:41,220 there are no instance variables which are specific to rebeling class knowledge or could some technical 56 00:04:41,220 --> 00:04:47,820 requirements that be how it would be nice if bookmark class is non instantiation. 57 00:04:47,820 --> 00:04:51,320 The reason is as mentioned earlier is just too generic. 58 00:04:51,380 --> 00:04:55,530 Or let's say abstract to have any implementation for one of its methods. 59 00:04:55,600 --> 00:04:58,520 Which is does the east Cutrone eligible method. 60 00:04:58,620 --> 00:05:01,460 So you can assume having an empty body for this method. 61 00:05:01,740 --> 00:05:06,560 So semantically it just doesn't make sense to create a bookmark object. 62 00:05:06,700 --> 00:05:12,360 Just imagine creating a bookmark object and then invoking the east get from the original method which 63 00:05:12,360 --> 00:05:14,940 simply doesn't have any implementation. 64 00:05:14,940 --> 00:05:19,010 It makes sense to invoke such a method on a movie or a book object. 65 00:05:19,360 --> 00:05:24,140 As these classes can define some specific criteria for this matter. 66 00:05:24,330 --> 00:05:31,250 So bookmark class should be non-instructional And can you think of any way to achieve this. 67 00:05:31,260 --> 00:05:37,540 No you miss it that we can have a private constructor as it prevents instantiation But we also know 68 00:05:37,540 --> 00:05:43,170 that it prevents inheritance so it doesn't work and we need something new. 69 00:05:44,050 --> 00:05:50,400 Now similarly another requirement is that it would be nice to avoid having empty body for ease geek 70 00:05:50,400 --> 00:05:53,430 friendly and jamon matter within the bookmark gloss. 71 00:05:53,730 --> 00:06:01,050 That is some kind of an explicit syntax to indicate that this method is too abstract to have any implementation 72 00:06:01,050 --> 00:06:01,770 . 73 00:06:02,130 --> 00:06:08,460 So these two requirements can be addressed by a new feature called abstract class which can how abstract 74 00:06:08,460 --> 00:06:09,880 methods. 75 00:06:09,990 --> 00:06:13,340 So next let's look at abstract losses and methods. 76 00:06:13,500 --> 00:06:13,890 Thank you