1 00:00:02,850 --> 00:00:10,410 Hi there this is going to do you know understand the motivation for the need for bondable cuts that 2 00:00:10,410 --> 00:00:16,710 make our ice flexible and in this lesson they will get into the details of bonded Walcott's And we'll 3 00:00:16,710 --> 00:00:22,740 also look at recommendations on grant to use them Dumay will be done in the follow up lesson and it's 4 00:00:22,740 --> 00:00:25,710 going to be a long lesson but an important one. 5 00:00:26,580 --> 00:00:30,250 Let's begin with upper bondable cuts in the previous lesson. 6 00:00:30,420 --> 00:00:36,570 We mentioned that in certain harmless scenarios we're type safety is not a concern invariant property 7 00:00:36,570 --> 00:00:37,750 can be restrictive. 8 00:00:38,220 --> 00:00:44,490 We set up on solution is to use genetic methods and we looked at it in the Dematteo of the solution 9 00:00:44,580 --> 00:00:46,730 was to use upper bondable cuts. 10 00:00:46,740 --> 00:00:48,370 And here is an example. 11 00:00:48,810 --> 00:00:55,590 The key word excellence is used and it can be read as a list of some subtype off book Walk. 12 00:00:55,950 --> 00:01:02,490 What it means is a video of such an upper bonded wild card type can be assigned to a list of bookmark 13 00:01:02,580 --> 00:01:05,880 on our list of book on our list of movie. 14 00:01:06,060 --> 00:01:12,210 Notice that even though we said it is a list off some subtype of bookmarked it can still be assigned 15 00:01:12,290 --> 00:01:13,880 a list of bookmarks. 16 00:01:13,970 --> 00:01:20,180 So subtype would also imply that every type is this a pipe of the supper table. 17 00:01:20,180 --> 00:01:27,990 Art is helping us to work on the inflexibility of invariants and we know that due to invariants we cannot 18 00:01:27,990 --> 00:01:29,070 do this. 19 00:01:29,070 --> 00:01:33,620 That is a list of book cannot be assigned to a list of bookmarks. 20 00:01:34,660 --> 00:01:40,950 On here it is the harmless display method that displays all the bookmarks in the input list and this 21 00:01:40,950 --> 00:01:41,920 method can be in more. 22 00:01:41,930 --> 00:01:47,260 But list off a bookmark or list off book or list of all the art list overbilling. 23 00:01:47,830 --> 00:01:52,670 And we also know that the same method can also be expressed using generic method. 24 00:01:52,680 --> 00:02:00,190 In this way not that unbonded wildcard simply implies that object is the ball. 25 00:02:00,330 --> 00:02:06,960 That is if you have a list of unbonded Volkart then we can assign it a list of object or list or any 26 00:02:06,960 --> 00:02:08,440 such type of object. 27 00:02:08,610 --> 00:02:16,500 Which means you can assign a list of anything as object as a supertype of all types as we just saw an 28 00:02:16,500 --> 00:02:19,920 unbonded Volkart is also an upper bonded ballcock. 29 00:02:19,920 --> 00:02:27,150 But that object as an invisible Baun and due to this upper bondable card also has the same compiler 30 00:02:27,150 --> 00:02:30,650 types if the restrictions as an unwanted Wilcott. 31 00:02:31,470 --> 00:02:37,500 That is we cannot invoke moppets that use class level type parameters with any arguments except none 32 00:02:37,510 --> 00:02:38,220 . 33 00:02:38,450 --> 00:02:44,910 So if the wildcard type is something like an idealist then we cannot invoke the augmented as the add 34 00:02:44,910 --> 00:02:47,720 method use asset class level type parameter. 35 00:02:47,880 --> 00:02:55,080 You can invoke it only by passing in this way pipes if he's unsure at compile time extension. 36 00:02:56,010 --> 00:03:02,220 This means that you can only do stuff like this by the input parameter x as a producer of data but does 37 00:03:02,220 --> 00:03:09,250 not and you need that is within the method the cannot access methods like ACTA But this up of underbite 38 00:03:09,260 --> 00:03:14,880 Godfrey church gives us the flexibility when it comes to passing off arguments. 39 00:03:14,890 --> 00:03:20,220 Also just keep in mind that all that genetic notation that you see here will not be there at runtime 40 00:03:20,220 --> 00:03:20,490 . 41 00:03:20,550 --> 00:03:22,730 It would be addressed off by the compiler. 42 00:03:22,800 --> 00:03:28,830 It is only to ensure that we are making the right invocations on right assignments both in the calling 43 00:03:28,830 --> 00:03:31,190 code as well as the matter. 44 00:03:31,290 --> 00:03:36,800 So at runtime the wildcard byte will simply be lost. 45 00:03:36,800 --> 00:03:41,330 Now if we want to consume the dot then we need to go with no what wanted wildcard. 46 00:03:41,460 --> 00:03:45,600 And we discussed it briefly in the previous season and here is an example. 47 00:03:45,780 --> 00:03:50,250 In the case of upper bonded wild card we use the P word extents on here. 48 00:03:50,280 --> 00:03:58,050 We use the key super and we can read it as list off some supertype of bookmark for a pointer wildcard 49 00:03:58,060 --> 00:03:58,100 . 50 00:03:58,140 --> 00:04:02,850 It was list off some subtype of a bookmark. 51 00:04:02,850 --> 00:04:09,300 So because we are using a super keyword what it means is a list of a bookmark at the lower one can be 52 00:04:09,300 --> 00:04:17,120 assigned a list of bookmark or a list of objects as object is a supertype of bookmark not dactylic subtype 53 00:04:17,120 --> 00:04:17,400 . 54 00:04:17,520 --> 00:04:22,100 In case of supertype you every type is a supertype of Xserve. 55 00:04:22,650 --> 00:04:26,850 Hence we are able to assign a list of bookmarks here. 56 00:04:27,270 --> 00:04:33,750 We however cannot assign not a list of books on another list of Maulvi as book and movie are subtypes 57 00:04:33,750 --> 00:04:34,520 of book. 58 00:04:35,130 --> 00:04:37,640 Doing so will give a compiler error. 59 00:04:37,650 --> 00:04:44,400 It's got to be a bookmark or it's super nice on here is a compiler restriction that would make an louvered 60 00:04:44,400 --> 00:04:51,000 bonded card type act as a consumer of data under the same time ensures that compile time types if the 61 00:04:51,000 --> 00:04:52,390 is not compromised. 62 00:04:52,710 --> 00:05:00,120 So the router is VIGEN equipment words that use class level type parameter only if argument is off longer 63 00:05:00,260 --> 00:05:08,530 bonder type or one of its subtypes here as an example which we also saw in the previous listen the method 64 00:05:08,560 --> 00:05:14,820 is Nimbus aggregate hundred use a silver bonded Whatcott type good book mark castable. 65 00:05:14,920 --> 00:05:21,160 So this method as we can see can be invoked with an idealist or bookmark or we can also invoke it with 66 00:05:21,160 --> 00:05:22,790 an other list of object. 67 00:05:23,120 --> 00:05:29,410 And but then the method has the lower bonders bookmark we can and will add that and pass a bookmark 68 00:05:29,410 --> 00:05:34,570 object or any of its subtypes like book or movie objects. 69 00:05:34,600 --> 00:05:37,820 So basically input list is consuming data. 70 00:05:38,140 --> 00:05:42,540 In the earlier example of the splintered input list was producing data. 71 00:05:42,610 --> 00:05:47,370 So here in booklist Attis a consumer on superspy would put into that. 72 00:05:47,770 --> 00:05:55,640 But if you use exc. word then input list x as a producer but not on the data just not the pipes if bees 73 00:05:55,640 --> 00:06:01,660 also respected here as the more specific argument that can be passed would be endless Stoffe bookmark 74 00:06:02,350 --> 00:06:08,080 which can contain bookmark or any of its type objects. 75 00:06:08,080 --> 00:06:11,730 This is the same aggregate method with the same method parameter type. 76 00:06:11,740 --> 00:06:18,320 The statements show that from the input list then we get an element it stipes should be off type object 77 00:06:18,330 --> 00:06:18,620 . 78 00:06:19,120 --> 00:06:20,500 So full statement is invalid. 79 00:06:20,520 --> 00:06:21,750 Well second is valid. 80 00:06:22,150 --> 00:06:28,750 False statement is invalid because if the method is in with a list of object then we get a class exception 81 00:06:29,080 --> 00:06:36,620 as object can not be trusted to bookmen unless we insert an explicit cast not duck. 82 00:06:36,670 --> 00:06:39,090 Lol what Baun is only for wildcards. 83 00:06:39,160 --> 00:06:45,130 It cannot be used with type parameters and when this occurs it applies to both generic types as well 84 00:06:45,130 --> 00:06:46,920 as generic methods. 85 00:06:47,440 --> 00:06:52,900 You know that extends keyword applies to parameters too. 86 00:06:53,050 --> 00:07:00,020 One other thing to note is that a wildcard can how only single upper are single lower bound. 87 00:07:00,430 --> 00:07:07,570 You know the type parameters and generic types on generic methods can have multiple bunchy on here is 88 00:07:07,570 --> 00:07:14,460 an important effective dollar item which is used bonded wildcards to increase API flexibility. 89 00:07:14,560 --> 00:07:20,470 We already discussed it and we said that was the motivation for using bonded carts are also generic 90 00:07:20,470 --> 00:07:21,180 methods. 91 00:07:21,550 --> 00:07:27,490 So if you're writing AB ice then you would want to see as bonded Woodcock's can be used for method parameters 92 00:07:28,210 --> 00:07:29,440 from a design standpoint. 93 00:07:29,500 --> 00:07:32,830 It would be great to use them whenever possible. 94 00:07:32,940 --> 00:07:36,580 Let's look at the specific suggestions from this item. 95 00:07:36,580 --> 00:07:42,240 If the input parametrized type produces data then we should use a put bondable cark. 96 00:07:42,370 --> 00:07:47,850 You saw this in the display method earlier and we already know this too. 97 00:07:48,040 --> 00:07:52,680 If input parameters type consumes data then use lower bonded wildcard. 98 00:07:53,130 --> 00:07:57,930 And you saw this in the aggregate Materne earlier. 99 00:07:57,940 --> 00:08:04,900 If input parametrized type produces data on you don't know or don't care what the pipe argument is in 100 00:08:04,900 --> 00:08:06,100 the invoking code. 101 00:08:06,310 --> 00:08:08,540 Then use unbonded wildcard. 102 00:08:09,280 --> 00:08:14,680 Just note that here we are seeing producing data support unbonded are upper bondable cards. 103 00:08:14,680 --> 00:08:20,870 Our producers are like we discussed earlier unbonded wild card is also an upper bondable card. 104 00:08:20,920 --> 00:08:28,870 It is just that it uses a more generic bound object so unbonded an upper bound it producers by no unbonded 105 00:08:28,870 --> 00:08:31,150 wild card is it concealment. 106 00:08:32,230 --> 00:08:33,810 And here is an interesting thing. 107 00:08:34,000 --> 00:08:40,110 If parameterize type Axel's book producer and consumer then you'll need to use an exact match. 108 00:08:40,120 --> 00:08:44,880 That is something like and less off book back then because you use white box. 109 00:08:45,340 --> 00:08:46,210 For instance. 110 00:08:46,310 --> 00:08:52,870 Cannot use operable hundred wild card as extents does not allow us to consume data right due to pipes 111 00:08:52,870 --> 00:08:54,720 or frustration. 112 00:08:54,730 --> 00:09:01,030 Similarly we can't use Lammert bonded well card as the problem will be with producing data. 113 00:09:01,150 --> 00:09:08,350 We know that within the method the input object that syndicalist can consume the louver bone on any 114 00:09:08,350 --> 00:09:09,970 of its subtypes. 115 00:09:09,970 --> 00:09:16,450 But when it comes to producing data there is no indeed that it would produce only more bone or any of 116 00:09:16,450 --> 00:09:17,930 its updates. 117 00:09:17,950 --> 00:09:24,370 That's because since the method can be invoked bit list off some supertype of the lower bound. 118 00:09:24,700 --> 00:09:31,690 It can also contain some supertype objects which can need do class const exceptions at runtime so it 119 00:09:31,690 --> 00:09:35,520 needs to be exact match Niguel list of bookmarks. 120 00:09:35,770 --> 00:09:41,520 That way you know that the list can always consume unproduced only bookmark objects or one of what's 121 00:09:41,650 --> 00:09:44,340 next. 122 00:09:44,350 --> 00:09:49,870 Finally in case you're having trouble remembering a bought producer and consumer then you can use this 123 00:09:49,870 --> 00:09:56,350 mnemonic packs which stands for user extents and guns you are super gay. 124 00:09:56,530 --> 00:09:58,810 So keep packs in mind. 125 00:09:58,840 --> 00:10:05,580 Also just note that this concept of producer and consumer is also often referred to as get put in. 126 00:10:05,640 --> 00:10:13,870 You can get for producing the DA while consuming get put principle also says if bought get and book 127 00:10:13,870 --> 00:10:18,350 happen then exact match is needed. 128 00:10:18,370 --> 00:10:23,530 Now let's quickly look at some real producer consumer amateur declarations from the Jaguar ocotillo 129 00:10:23,530 --> 00:10:30,250 collections costs here the comment method is add on which is a generic method and it acts on the specified 130 00:10:30,280 --> 00:10:35,050 elements to the specified collection see which is the parameter. 131 00:10:35,060 --> 00:10:38,690 So collection is going to consume elements are enhanced. 132 00:10:38,730 --> 00:10:39,210 Super. 133 00:10:39,260 --> 00:10:43,250 What is your extra copy method. 134 00:10:43,300 --> 00:10:49,720 It copies all the elements in source list in the destination list destination list is the hospital magor 135 00:10:50,620 --> 00:10:51,490 so socialist. 136 00:10:51,490 --> 00:10:54,040 Here is the producer and hence excellence. 137 00:10:54,040 --> 00:10:54,970 Q What is yours. 138 00:10:55,150 --> 00:10:56,620 Why the destination list. 139 00:10:56,620 --> 00:10:58,630 Is the consumer on hence super. 140 00:10:58,630 --> 00:11:04,460 Q What is your next it's a dis dramaturg under-treated answer group. 141 00:11:04,510 --> 00:11:11,200 If they do and book collections have more elements in common on here and unbonded wild card is used 142 00:11:11,470 --> 00:11:16,870 because we really don't care about the type of elements in the collection model work. 143 00:11:16,880 --> 00:11:23,500 They are producers of data that is only the elements are iterated and unknown data is added into the 144 00:11:23,500 --> 00:11:25,260 collections. 145 00:11:25,420 --> 00:11:26,890 So data is just compare. 146 00:11:27,220 --> 00:11:29,710 But no data is entered into the collections. 147 00:11:29,710 --> 00:11:34,380 So unbonded wild wildcards should be used for such cases. 148 00:11:34,400 --> 00:11:41,620 Our next is replace on Widgery places on occurrences of one value in a less that and value hit an exact 149 00:11:41,620 --> 00:11:46,240 match as needed as just as put producing as well as consuming data. 150 00:11:46,390 --> 00:11:50,680 For instance here is the relevant code fragment from this method. 151 00:11:50,710 --> 00:11:55,990 Here is the list as being it record it checks if the current element is equal to only 1. 152 00:11:56,440 --> 00:12:02,380 So the list is acting as a producer here and if the current element is equal to all valid then it is 153 00:12:02,380 --> 00:12:09,760 being replaced bit Newble thereby making the list act as a consumer as the statement that uses class 154 00:12:09,790 --> 00:12:12,050 global parameters. 155 00:12:12,100 --> 00:12:16,520 So in this case we need to use an exact match on wildcards should not be used. 156 00:12:16,660 --> 00:12:22,600 As discussed earlier in the follow up lesson we will leave them all under or we will see how these methods 157 00:12:22,600 --> 00:12:24,820 can be actually invoked. 158 00:12:25,060 --> 00:12:26,210 So that's all for now. 159 00:12:26,410 --> 00:12:27,450 Just to summarize. 160 00:12:27,470 --> 00:12:35,200 Remember Doc bonded while costs can make your API very flexible and not that extends to what is used 161 00:12:35,380 --> 00:12:36,800 when you want to produce data. 162 00:12:36,850 --> 00:12:40,650 Well Superguy word is used when you want to consume data. 163 00:12:40,830 --> 00:12:41,430 All right then. 164 00:12:41,440 --> 00:12:42,070 Thank you. 165 00:12:42,100 --> 00:12:43,430 See you in the demo.