1 00:00:01,000 --> 00:00:02,700 Work and let's look at hash map. 2 00:00:03,000 --> 00:00:08,480 But before going to the mall let's look at a few important things which are relevant to hash map. 3 00:00:09,000 --> 00:00:13,830 I think we already discussed most of these points but let's do it one more time just for the sake of 4 00:00:13,830 --> 00:00:15,550 completeness. 5 00:00:15,600 --> 00:00:23,310 The methods get undermost brook and Constantine and that hash map insertion order is not preserved as 6 00:00:23,310 --> 00:00:29,440 the elements are stored based on using it hash function hash map but it's not a lot of use. 7 00:00:29,520 --> 00:00:31,460 And also one Halki. 8 00:00:31,980 --> 00:00:37,020 Finally two methods are not synchronized unlike that legacy hash table class. 9 00:00:37,050 --> 00:00:41,590 Now if synchronization is required it can always be taken care of externally. 10 00:00:41,790 --> 00:00:45,160 As you'll see later when we get to the might be trading partner. 11 00:00:45,510 --> 00:00:46,680 So that's about it. 12 00:00:46,680 --> 00:00:54,450 And it's not time for that Demel took it for this demo a new class called map the more has been added 13 00:00:54,450 --> 00:00:57,170 to the collections package just like bless them all. 14 00:00:57,180 --> 00:00:58,810 I answered them all. 15 00:00:58,860 --> 00:01:03,850 So in my of them all we have this matter hashmarks them all which we are going to fill now. 16 00:01:03,870 --> 00:01:10,200 So in this demo they will test all the basic operations which we have seen earlier and we will also 17 00:01:10,200 --> 00:01:12,250 look at how to iterate a map. 18 00:01:12,510 --> 00:01:14,840 So we will be looking at the human. 19 00:01:14,910 --> 00:01:20,850 So using the view that we can do it and initially we will create a simple hazmat later we will also 20 00:01:20,850 --> 00:01:24,060 create a slightly more complex hash map. 21 00:01:24,090 --> 00:01:26,330 So let's just go ahead and create a hash map. 22 00:01:27,200 --> 00:01:29,770 That said the key is string. 23 00:01:30,300 --> 00:01:35,980 So that's the generic notation. 24 00:01:36,420 --> 00:01:40,250 So let me import let me just do a control of all. 25 00:01:41,110 --> 00:01:43,250 And that automatically imported. 26 00:01:43,290 --> 00:01:46,770 So here the brackets are empty here. 27 00:01:46,980 --> 00:01:50,590 Just know that we can also have a string on integer specified here. 28 00:01:50,640 --> 00:01:54,020 But it is automatically inferred by the compiler. 29 00:01:54,060 --> 00:01:57,250 So here we are programming to an interface your map. 30 00:01:57,250 --> 00:01:58,770 And so we have created the hash map. 31 00:01:58,830 --> 00:02:00,300 Let's go and put some elements here 32 00:02:00,310 --> 00:02:06,350 . 33 00:02:12,600 --> 00:02:16,520 So here us three users John-Roger to iron. 34 00:02:16,520 --> 00:02:19,260 Let's say these are their ages and we're on it. 35 00:02:19,260 --> 00:02:21,410 Let's leave the value as another. 36 00:02:21,620 --> 00:02:22,660 OK. 37 00:02:22,800 --> 00:02:24,360 Now let's just print this 38 00:02:27,090 --> 00:02:29,740 space map one. 39 00:02:30,300 --> 00:02:31,510 So let me just run this. 40 00:02:31,510 --> 00:02:37,960 It's in from the main You can search prints all of the values your key value pairs. 41 00:02:38,520 --> 00:02:41,540 Now let's all right. 42 00:02:41,560 --> 00:02:44,100 And it does mapping and axis and map. 43 00:02:44,180 --> 00:02:48,320 My one word. 44 00:02:48,930 --> 00:02:49,410 All right. 45 00:02:49,420 --> 00:02:52,100 You let's just put some value here on the tree. 46 00:02:52,300 --> 00:02:52,780 And 47 00:02:57,810 --> 00:03:02,010 so as you can see the only value got over it and the new one. 48 00:03:02,050 --> 00:03:03,180 OK. 49 00:03:04,350 --> 00:03:07,840 Now let's try the contains ski operation. 50 00:03:08,250 --> 00:03:09,510 So let me just say 51 00:03:15,150 --> 00:03:19,050 map 1. 52 00:03:19,050 --> 00:03:21,780 Lewinsky and it's just search for John 53 00:03:24,750 --> 00:03:26,240 and it says Drew. 54 00:03:26,410 --> 00:03:27,090 OK. 55 00:03:27,390 --> 00:03:30,940 Now let's get a value. 56 00:03:30,960 --> 00:03:32,990 So this is an Bensky operation that are done. 57 00:03:33,000 --> 00:03:34,020 True. 58 00:03:34,110 --> 00:03:37,890 Now given a key just fetched the values so that's the lookup operation. 59 00:03:37,890 --> 00:03:43,020 That's the most commonly used operation with the hash map. 60 00:03:43,050 --> 00:03:47,160 So let's get John's age now. 61 00:03:48,270 --> 00:03:52,440 So we need to use get and John. 62 00:03:53,480 --> 00:03:54,150 OK. 63 00:03:54,180 --> 00:03:57,240 So that's the H here. 64 00:03:57,240 --> 00:04:01,970 Now let's just go ahead and do it through the map. 65 00:04:02,040 --> 00:04:03,100 OK. 66 00:04:03,120 --> 00:04:04,880 So let's try hard but it don't matter. 67 00:04:04,950 --> 00:04:10,220 There are a couple of ways to do it. 68 00:04:14,190 --> 00:04:16,690 So first let's try to do that using the keyset method. 69 00:04:16,770 --> 00:04:19,830 So keyset is one of the collection methods. 70 00:04:19,860 --> 00:04:21,560 So let's get the research. 71 00:04:21,560 --> 00:04:27,870 So let's just extract the keyset and for that we can use the keys at method. 72 00:04:28,410 --> 00:04:31,090 So keyset what we've done is set. 73 00:04:31,320 --> 00:04:33,960 So we call on the set of all keys. 74 00:04:33,990 --> 00:04:41,720 So it's names you do control shift 0 9. 75 00:04:41,910 --> 00:04:44,150 So use a for each statement. 76 00:04:44,840 --> 00:04:46,530 I did it over the names. 77 00:04:46,580 --> 00:04:48,420 OK. 78 00:04:55,040 --> 00:05:03,950 Now we can say my plan got get all the name of the careers of the current name. 79 00:05:04,500 --> 00:05:04,960 OK. 80 00:05:05,030 --> 00:05:08,550 So let's just run it. 81 00:05:08,600 --> 00:05:15,920 So here we are reading using keyset and we redid it in over all the names all the keys and for each 82 00:05:15,920 --> 00:05:19,420 name we are we are fetching the corresponding h. 83 00:05:19,430 --> 00:05:19,990 OK. 84 00:05:20,330 --> 00:05:26,210 So that's one way off iterating on the second way as we can also do read using the entry set method 85 00:05:26,230 --> 00:05:26,290 . 86 00:05:26,330 --> 00:05:28,540 OK so let's also do that. 87 00:05:28,610 --> 00:05:33,060 So the entry cert Vawdrey done a set of all mappings. 88 00:05:33,200 --> 00:05:39,190 Let me just say. 89 00:05:42,180 --> 00:05:53,750 And in this case it will be set off if you recall it would return an instance of the the entry interface 90 00:05:53,780 --> 00:05:56,000 and we said it was an upstart interface. 91 00:05:56,000 --> 00:06:01,900 So each mapping would be an instance of this particular nested interface and tree. 92 00:06:02,180 --> 00:06:05,880 And the key value for that is we know that it's a strain. 93 00:06:05,990 --> 00:06:09,520 Each entry is a string and the value is integer. 94 00:06:09,780 --> 00:06:11,580 OK. 95 00:06:13,520 --> 00:06:17,960 Just don't worry if it is a little bit confusing with the generics notations. 96 00:06:18,170 --> 00:06:22,190 I think it will get uglier when we get to when we discuss genetics. 97 00:06:22,190 --> 00:06:25,570 So now let's go ahead and iterate through this. 98 00:06:25,640 --> 00:06:28,980 So here let's change your two mappings. 99 00:06:30,330 --> 00:06:33,520 And here this would be let's just call. 100 00:06:33,560 --> 00:06:34,820 Does not being. 101 00:06:35,570 --> 00:06:41,760 And that type would be this would be done by the way. 102 00:06:42,050 --> 00:06:48,680 Now for Meem we can just say my being d'arte get. 103 00:06:48,950 --> 00:06:52,530 So this is one of the methods and entry interface. 104 00:06:52,790 --> 00:07:03,470 Ok and for H It just see Dot get right you can not see. 105 00:07:03,770 --> 00:07:06,230 So it's just going to print on the values. 106 00:07:06,230 --> 00:07:09,460 So this is just an alternative way off iterating. 107 00:07:09,470 --> 00:07:15,560 Personally I would prefer this one for iterating because you know we are fetching all of the entries 108 00:07:15,650 --> 00:07:21,130 and all we need to do is invoke that for each entry we are invoking the get an get value had us here 109 00:07:21,140 --> 00:07:21,160 . 110 00:07:21,170 --> 00:07:22,280 This is also fast. 111 00:07:22,280 --> 00:07:25,780 We are iterating through to each of the keys. 112 00:07:26,090 --> 00:07:28,510 But then here we are doing a search. 113 00:07:28,700 --> 00:07:33,740 Most of the time it's going to be constant don't really know but sometimes you know if a lot of these 114 00:07:33,740 --> 00:07:38,530 get mapped to one particular bucket then it can be slightly ex-manager. 115 00:07:38,690 --> 00:07:41,600 So probably this is a better way of doing it. 116 00:07:41,600 --> 00:07:41,830 OK. 117 00:07:41,840 --> 00:07:43,870 So we are done with that. 118 00:07:44,030 --> 00:07:50,440 Now what we can do is we know that this return set is back but the original set. 119 00:07:50,600 --> 00:07:57,590 So any changes we make here will impact the bact and the actual map also the Mac actual hash map. 120 00:07:57,620 --> 00:07:59,250 So that sort of tells that. 121 00:07:59,300 --> 00:08:06,750 So here let's just say names doddery more on that just right the remote. 122 00:08:06,800 --> 00:08:07,310 Anita 123 00:08:12,030 --> 00:08:18,540 So you run it as we can see we only see John and Raaj and the mapping corresponding and corresponding 124 00:08:18,540 --> 00:08:20,450 to on it got deleted. 125 00:08:20,450 --> 00:08:26,750 So that's about it that's the simple hash map lets start to create a slightly more complex hash map 126 00:08:27,170 --> 00:08:30,840 so that we can see how flexible lead can be used. 127 00:08:30,870 --> 00:08:34,700 So earlier it was a map of string and integer. 128 00:08:34,700 --> 00:08:37,850 Now let's create a map of string and Adorama. 129 00:08:37,880 --> 00:08:42,230 So the value will also be map I guess to do that. 130 00:08:42,260 --> 00:08:45,380 So let's say map. 131 00:08:45,590 --> 00:08:48,120 Now this map let's have string. 132 00:08:48,560 --> 00:08:50,960 So earlier it was name and age. 133 00:08:50,960 --> 00:08:53,130 Now here let's say this is the name. 134 00:08:53,300 --> 00:08:56,980 And here will how a list of key value pairs. 135 00:08:57,050 --> 00:09:00,050 So this would be some profile information of each user. 136 00:09:00,080 --> 00:09:03,870 So we can now age department and stuff like that. 137 00:09:04,160 --> 00:09:04,430 OK. 138 00:09:04,430 --> 00:09:06,370 So this earlier we had only h. 139 00:09:06,410 --> 00:09:07,870 So one value was good enough. 140 00:09:07,880 --> 00:09:15,050 But since the how we want to maintain a list of values as part of the profile let's maned Let's use 141 00:09:15,050 --> 00:09:16,510 a map here. 142 00:09:16,970 --> 00:09:24,830 But instead of integer here let's say object so that we can store you know if it is an age it could 143 00:09:24,830 --> 00:09:27,280 be integer if it is city to be string. 144 00:09:27,350 --> 00:09:31,380 Ok so let's use a more generic object here. 145 00:09:31,730 --> 00:09:36,480 It's called This Prufrock user profile. 146 00:09:38,810 --> 00:09:39,020 OK. 147 00:09:39,020 --> 00:09:44,430 So next steps just create this object here for this. 148 00:09:44,910 --> 00:09:49,400 So let's just copy this. 149 00:09:50,430 --> 00:09:52,780 It's called a profile 150 00:09:55,780 --> 00:09:58,430 not its actual values 151 00:10:05,310 --> 00:10:12,670 that department says. 152 00:10:12,890 --> 00:10:19,270 And it's also the city of the user that say New York. 153 00:10:20,180 --> 00:10:21,660 OK so that's that. 154 00:10:21,990 --> 00:10:27,520 And next we need to add it to user profile. 155 00:10:29,240 --> 00:10:32,070 Under law you would be fine. 156 00:10:32,750 --> 00:10:33,710 So that's it. 157 00:10:33,710 --> 00:10:42,310 And let's also create one more user to use the same profile variable that age. 158 00:10:42,450 --> 00:10:46,710 Roger a destroying design department we can be right. 159 00:10:46,740 --> 00:10:48,150 Yes you are. 160 00:10:48,170 --> 00:10:56,480 And let's just put the second user let's it's that Raj. 161 00:10:56,540 --> 00:10:59,580 So those are the two users. 162 00:10:59,630 --> 00:11:01,460 Let's just go ahead and bring them 163 00:11:01,460 --> 00:11:10,370 . 164 00:11:10,850 --> 00:11:14,300 So as you can see it is printing the values so first one is John. 165 00:11:14,300 --> 00:11:19,320 This is the key and this is the value which is Nestor's map. 166 00:11:19,730 --> 00:11:22,510 OK Sambit here Raj under-invested map. 167 00:11:22,650 --> 00:11:23,730 OK. 168 00:11:24,110 --> 00:11:33,270 Now let's just go ahead and just retrieve the value of the information about about the first user who 169 00:11:33,340 --> 00:11:34,070 John. 170 00:11:34,100 --> 00:11:35,080 So let's just say 171 00:11:38,570 --> 00:11:41,960 say profile one equal to 172 00:11:45,000 --> 00:11:48,080 get would be John. 173 00:11:48,080 --> 00:11:53,450 So the type here would be map all string an object and that's the profile of the user John. 174 00:11:53,480 --> 00:11:58,770 So let's just go ahead and see and age. 175 00:11:58,790 --> 00:12:00,500 Let's just get the age value. 176 00:12:00,740 --> 00:12:09,800 So we need to do profile one not get of age but this one returns an object. 177 00:12:09,830 --> 00:12:19,390 So we need to downcast it because it's an object here and you're not allowed to just simply print it 178 00:12:19,570 --> 00:12:23,630 out age. 179 00:12:24,440 --> 00:12:25,070 That's it. 180 00:12:25,070 --> 00:12:26,840 So it's run out. 181 00:12:27,230 --> 00:12:33,210 And as you can see the age 25 has been extracted from the profile and it's printed here. 182 00:12:33,680 --> 00:12:34,600 So that's about it. 183 00:12:34,670 --> 00:12:36,230 So that's the hash map. 184 00:12:36,440 --> 00:12:39,330 So I would like to give a small exercise for you. 185 00:12:39,380 --> 00:12:40,700 Just go ahead and try. 186 00:12:40,700 --> 00:12:46,410 There is a second constructor in the constructor that we used was a constructor that is also of the 187 00:12:46,410 --> 00:12:48,330 constructor which takes another map. 188 00:12:48,650 --> 00:12:51,010 And it just creates a new map. 189 00:12:51,040 --> 00:12:51,280 OK. 190 00:12:51,290 --> 00:12:54,040 So I would like you to look at the API and try that out. 191 00:12:54,070 --> 00:12:56,120 And also we did not try to put all matter. 192 00:12:56,120 --> 00:13:02,960 You can also try that and you can also try all other matters like clear and size and there is one View-Master 193 00:13:03,050 --> 00:13:07,290 values which would return the collection of all the values in the hash map. 194 00:13:07,410 --> 00:13:09,420 So you can also try that out. 195 00:13:09,890 --> 00:13:16,850 So in the next lesson we will extend this demo because we want we said that we the keys. 196 00:13:16,850 --> 00:13:19,140 Generally it has to be immutable objects. 197 00:13:19,490 --> 00:13:24,550 But if it if it is a mutable object then we need to be very careful. 198 00:13:24,740 --> 00:13:29,930 So we will do all of that and we will see what kind of problem we can have. 199 00:13:30,170 --> 00:13:32,330 If you use a mutable object as the key. 200 00:13:32,540 --> 00:13:34,210 So that will be the next lesson. 201 00:13:34,250 --> 00:13:34,780 Thank you. 202 00:13:34,790 --> 00:13:35,650 Happy coding. 203 00:13:35,670 --> 00:13:37,560 And you can find the code in the resources section