WEBVTT 00:00.860 --> 00:01.430 Hi everyone. 00:01.430 --> 00:02.720 Welcome back to this tutorial. 00:02.720 --> 00:09.920 In this tutorial I will talk some theory about Streams API and then we will implement a simple use case. 00:10.070 --> 00:13.610 Streams API got introduced in Java eight. 00:13.850 --> 00:20.480 The main purpose of streams API is to perform some kind of operation on a collection, meaning the collection 00:20.480 --> 00:25.400 could be a set list, linked list or map and et-cetera. 00:25.430 --> 00:31.730 You might be wondering why collection write any experienced Java developer out there knows the importance 00:31.730 --> 00:32.720 of collections. 00:32.750 --> 00:38.540 Collections help you group organize the data in our in your application. 00:38.750 --> 00:45.140 Basically any Java application that is out there, you heavily uses the collections. 00:46.400 --> 00:51.620 Even parallel operations are really easy to perform using streams API. 00:52.070 --> 00:53.840 That wasn't the case before. 00:54.060 --> 01:01.280 Forkjoin, which got introduced as part of Java seven, made it easier to perform parallel operation, 01:01.280 --> 01:04.670 but Streams API made it really simpler. 01:06.220 --> 01:12.040 API can also be used alongside with arrays or any kind of iOS. 01:13.370 --> 01:15.350 We talked about streams a bit. 01:15.380 --> 01:18.380 Now let's talk about what is a stream in general. 01:18.800 --> 01:25.640 A stream is a sequence of elements that are created from a collection, are arrays or any kind of IO. 01:25.700 --> 01:29.480 The next question that might be running in your mind is how do we create it? 01:29.480 --> 01:30.110 Right? 01:30.290 --> 01:31.730 Let's take a look at this example. 01:31.730 --> 01:34.640 We have a list of names which is of type list. 01:34.760 --> 01:36.410 We all know list is a collection. 01:36.440 --> 01:40.520 The way to create a stream out of it is by calling the stream method. 01:41.310 --> 01:44.250 This will create a stream of strings for you. 01:45.540 --> 01:51.960 As I mentioned before, streams operations can be performed sequentially or in parallel. 01:52.170 --> 01:53.640 How do we create a parallel stream? 01:53.640 --> 01:54.270 Right. 01:54.480 --> 02:01.410 Replace the stream with a parallel stream method that will help performing the stream operations in 02:01.410 --> 02:02.190 parallel. 02:02.220 --> 02:05.670 It is that simple to create a parallel stream. 02:05.970 --> 02:09.630 Now let's go ahead and code a simple example. 02:09.990 --> 02:11.610 I have the IntelliJ open. 02:11.640 --> 02:12.510 There you go. 02:12.660 --> 02:16.380 Now the first step is I'm going to create a package called streams. 02:18.670 --> 02:22.750 And then I'm going to create a class called Streams example. 02:27.500 --> 02:31.800 And I'm going to make this class executable by adding public static void main method. 02:32.370 --> 02:32.970 There you go. 02:33.000 --> 02:40.170 The first step is we'll code the use case where I want the student and their list of activities in a 02:40.170 --> 02:40.680 map. 02:40.710 --> 02:44.730 How do we implement that use case using streams API. 02:44.760 --> 02:46.200 So the use cases. 02:47.570 --> 02:48.260 The name. 02:50.900 --> 02:53.600 And their activities. 02:54.580 --> 02:55.110 No map. 02:55.900 --> 02:56.290 Okay. 02:57.430 --> 03:03.580 So we we know the student database class has a method called get all students, which is going to return 03:03.580 --> 03:06.160 you all the students in the collection. 03:06.550 --> 03:07.000 Here we go. 03:07.000 --> 03:08.110 We have six students. 03:08.320 --> 03:14.410 My use case is to have the student as a key and these list of activities as a value. 03:15.050 --> 03:15.930 I recorded. 03:16.230 --> 03:20.700 The first step is we are going to create the stream by calling the stream method. 03:21.180 --> 03:21.600 Good. 03:21.630 --> 03:27.420 The next step is we are going to use a method called collect. 03:28.790 --> 03:33.230 And there is another class called collectors. 03:35.870 --> 03:39.170 That is going to have a method called to map. 03:39.800 --> 03:40.370 There you go. 03:40.370 --> 03:43.880 We're going to use this method and if you take a look at it, it is using the. 03:45.330 --> 03:50.520 Go to the method and then check it is using the function as the first parameter and again function as 03:50.520 --> 03:51.810 a second parameter. 03:51.810 --> 03:54.210 We are going to make use of this. 03:55.400 --> 03:55.970 Method. 03:57.140 --> 03:59.750 So here we are going to provide. 03:59.960 --> 04:00.680 Student. 04:02.050 --> 04:04.120 We are going to use the method reference. 04:05.010 --> 04:05.820 It name. 04:07.700 --> 04:09.110 Let's import the student. 04:10.780 --> 04:15.490 As soon as I give the method reference syntax, it is going to give me the recommendation to use them 04:15.490 --> 04:17.560 name followed by that. 04:17.770 --> 04:18.730 What do we want? 04:19.330 --> 04:19.870 We want. 04:19.900 --> 04:20.980 Student Colon. 04:20.980 --> 04:21.580 Colon. 04:22.750 --> 04:23.980 IT activities. 04:25.620 --> 04:27.290 So this is returning a map. 04:27.300 --> 04:34.440 I'm going to create a map of string followed by the list of. 04:35.090 --> 04:38.690 Activities meaning list of string which has the activities. 04:39.260 --> 04:41.030 Let's give it a name for this one. 04:41.330 --> 04:47.180 Import this Java.util map, import this Java.util package. 04:47.180 --> 04:49.760 So this is like a student map. 04:50.890 --> 04:51.250 Going to. 04:51.760 --> 04:53.650 I'm going to print the. 04:55.310 --> 04:55.530 Button. 04:55.550 --> 04:55.820 Map. 04:58.440 --> 04:58.940 There you go. 04:58.950 --> 05:02.670 Now the next step, what I'm going to do, I'm going to run this example. 05:07.920 --> 05:12.540 So here it printed the student and the list of activities. 05:13.110 --> 05:17.880 Let's take a look at the example that we coded in one of our previous tutorial where let's take a look 05:17.880 --> 05:19.560 at this by function example. 05:19.590 --> 05:25.770 Here also, we have created a map with the student name as a key and the GPA as a value. 05:25.770 --> 05:29.370 But if you take a look at the code comparing this to the streams. 05:31.210 --> 05:36.370 For the number of lines of code and how descriptive this particular code is. 05:36.370 --> 05:37.660 It is more readable. 05:37.690 --> 05:39.780 That's one of the advantage with streams. 05:40.780 --> 05:47.830 You might be wondering, I said the same thing for lambdas, but now I'm saying that streams API is 05:47.830 --> 05:49.150 better than lambdas. 05:49.180 --> 05:50.350 The answer is no. 05:50.350 --> 05:52.600 That was not my intention at all. 05:53.110 --> 05:56.470 Streams API and lambdas go hand in hand. 05:56.500 --> 06:00.670 Now let's enhance this use case by adding more conditions to it. 06:00.700 --> 06:06.910 Now I want just the students who are in the grade level greater than or equal to three. 06:06.940 --> 06:09.800 In that case, how do I implement that? 06:09.820 --> 06:10.420 Right. 06:10.420 --> 06:17.580 There is a method called filter, which is part of the streams API, which is going to use lambdas. 06:17.590 --> 06:21.710 So if you go and take a look at the filter implementation, it accepts a predicate. 06:21.730 --> 06:25.390 So we are going to implement the predicate using the lambda. 06:25.930 --> 06:33.880 So here it is going to give you a student list stream of students because we have created a. 06:35.160 --> 06:35.550 Dream. 06:35.550 --> 06:40.300 All of this list of students, basically, that will help you create a stream of students. 06:40.320 --> 06:42.690 Now it is going to accept a student. 06:43.660 --> 06:48.700 Our filter is student dot get grade level. 06:49.430 --> 06:50.660 Greater than or equal to three. 06:51.080 --> 06:56.390 So right now in here, we have six students in the result. 06:56.870 --> 06:57.410 Okay. 06:57.410 --> 07:00.630 Now the use cases, we have applied this filter. 07:00.650 --> 07:06.800 Let's see how many number of students are going to be printed as a result of that filter. 07:09.120 --> 07:14.790 As you see right now, we just have three students, not not three students, four students who are 07:14.790 --> 07:16.500 matching this filter criteria. 07:17.040 --> 07:22.230 I'm going to enhance this use case by creating a predicate. 07:24.820 --> 07:25.690 Of shouldn't. 07:27.860 --> 07:29.900 I'm going to name this one as predicate student. 07:30.730 --> 07:31.690 And then. 07:33.750 --> 07:35.610 Goodness, Right. 07:35.910 --> 07:39.870 So here we have created a predicate. 07:39.900 --> 07:45.570 Now we can parse this predicate in this API filter. 07:46.530 --> 07:49.290 But understand is going to give me the same result. 07:49.560 --> 07:53.370 Now the next step is I want to apply another level of filtering. 07:55.390 --> 07:59.650 So I'm gonna name this one as student predicate. 08:00.850 --> 08:04.940 Yet GPA is greater than or equal to 3.9. 08:04.960 --> 08:10.490 That's a condition I want to apply for this existing filter so we already have a filter. 08:10.510 --> 08:15.370 Let's apply one more filter that's going to be student GPA predicate. 08:15.850 --> 08:20.200 Now let's go ahead and check what is the result that it is going to print. 08:24.510 --> 08:25.590 Running this. 08:26.340 --> 08:26.850 Here we go. 08:27.120 --> 08:29.250 It printed three students. 08:29.250 --> 08:31.230 Let's go and check the database class. 08:32.630 --> 08:35.240 So here we have. 08:36.390 --> 08:37.670 One, two, three, four. 08:37.680 --> 08:39.160 How many students that got printed? 08:39.180 --> 08:41.760 We have three students who got printed. 08:42.030 --> 08:49.230 Sophia wasn't there because she is not having the level greater than or equal to 3.9. 08:50.940 --> 08:53.700 If I comment this code, it is going to. 08:54.850 --> 08:56.800 You mean for students? 08:56.830 --> 09:02.650 If I enable this filter, it is giving me three students and that is what is expected. 09:03.010 --> 09:10.930 So it is that simple to perform these kind of manipulations in streams API. 09:11.200 --> 09:16.210 Basically, this is what I have observed from my experience of teaching first time. 09:16.210 --> 09:20.850 When you look at something new, either it is a syntax or a new way of programming. 09:20.860 --> 09:27.160 It might not be clear at that moment, but the next time when you look at it, it is it will clear. 09:27.160 --> 09:31.570 And then when you actually work on it, it will be more clear. 09:31.750 --> 09:36.820 Let's say I want to create a parallel stream instead of a stream is very simple. 09:36.880 --> 09:43.420 Now the filtering operations and all these collect operations are going to be performed in parallel 09:43.420 --> 09:44.080 manner. 09:44.540 --> 09:45.130 Run it. 09:45.670 --> 09:52.390 The result is going to be the same, but under the hood it is running all the operations in parallel. 09:53.760 --> 09:55.560 Let's not worry about parallel streams. 09:55.560 --> 09:55.890 Now. 09:55.890 --> 10:00.990 I have a separate section planned in the future tutorials of this course that will cover more details 10:00.990 --> 10:02.050 on this topic. 10:02.070 --> 10:08.700 One more thing I would like to highlight here is that streams API manipulate the collections in a declarative 10:08.700 --> 10:09.120 way. 10:09.150 --> 10:15.840 What does it mean is that instead of writing the code on how to implement the logic, just ask the desired 10:15.840 --> 10:19.980 result using the functions that are already part of the streams API. 10:20.010 --> 10:23.460 So here we have passed the filter predicate, right? 10:23.460 --> 10:25.110 The student predicate to this filter method. 10:25.140 --> 10:31.320 We don't care how it is going to implement or use that predicate to give you the desired result. 10:32.010 --> 10:38.100 A very good analogy for this style of programming, which is declarative programming is SQL. 10:38.250 --> 10:40.680 We run queries against the database tables. 10:40.680 --> 10:45.810 We don't care the computation that it performs behind the scenes to give you the desired result. 10:45.930 --> 10:47.970 We just focus on getting the result. 10:48.860 --> 10:52.160 Let's discuss more on the streams in the following sections. 10:52.190 --> 10:53.460 With this, we came to the end of.