WEBVTT 00:00.350 --> 00:00.980 Hi everyone. 00:00.980 --> 00:02.360 Welcome back to this tutorial. 00:02.360 --> 00:06.710 In this tutorial I will be explaining about how Stream API works. 00:06.710 --> 00:12.770 I would say this is one of the important tutorial in which I will be covering the Fundamentals of Streams 00:12.770 --> 00:13.520 API. 00:13.520 --> 00:18.920 I would highly recommend you guys to pay more attention to this content before we get into the internals 00:18.920 --> 00:24.470 of the Stream API, let's run the example which we coded in the previous tutorial and then find the 00:24.470 --> 00:25.190 result. 00:26.770 --> 00:30.400 So this is an example which we coded in the previous tutorial. 00:30.400 --> 00:34.090 I'm going to run this again and then validate the result. 00:34.090 --> 00:39.310 The result is having a hashmap with a string as a key, which is a name, and the list of activities 00:39.310 --> 00:41.800 as a value which is of type array list. 00:42.070 --> 00:42.850 That's good. 00:42.850 --> 00:49.630 Let's discuss about what happens after the completion of each and every step before the output is bundled 00:49.630 --> 00:50.920 into the map. 00:50.920 --> 00:54.880 Here we have to filter operations and then the collect operations. 00:54.880 --> 01:00.580 So what happens after the completion of each and every operation? 01:00.610 --> 01:04.120 That is something which I'm going to explain it using the presentation. 01:04.150 --> 01:06.010 Let us go back to the presentation. 01:06.010 --> 01:06.850 There you go. 01:10.030 --> 01:10.780 In this slide. 01:10.780 --> 01:16.810 I have the stream operations mentioned in the left side, and then the result of each and every operation 01:16.810 --> 01:21.160 is mentioned in the right side under the output column. 01:21.280 --> 01:28.960 All these operations together form a pipeline called the Stream pipeline, which starts from number 01:28.960 --> 01:30.880 one to number four. 01:31.610 --> 01:35.810 Each and every operation in this returns a string. 01:37.140 --> 01:43.050 There are two more definitions here, which are intermediate operations and terminal operations. 01:44.530 --> 01:50.830 The stream operations that happens between the stream method and the collect method are called intermediate 01:50.830 --> 01:51.970 operations. 01:53.750 --> 01:57.830 Here we just have the filter method in general for streams. 01:58.250 --> 02:03.650 It is not restricted to have just the filter method as intermediate operations. 02:03.680 --> 02:09.800 There are many different intermediate operations which I will be covering in the future tutorials. 02:10.850 --> 02:13.580 The next one is a terminal operation here. 02:13.580 --> 02:17.270 The terminal operations that we have covered is a collect. 02:18.290 --> 02:21.870 Again, collect is not the only terminal operations. 02:21.890 --> 02:27.590 There are many different terminal operations which I will be covering in the upcoming tutorials. 02:27.890 --> 02:33.200 For now, you just need to have an understanding of the definition of what is an intermediate operation 02:33.200 --> 02:35.570 and what is a terminal operation. 02:35.600 --> 02:39.080 Now let's go through the operations one by one. 02:39.830 --> 02:40.910 First operation. 02:40.910 --> 02:48.560 Here we are invoking a stream which creates a stream of students, which is nothing but a sequence of 02:48.560 --> 02:49.970 students, as you see here. 02:50.510 --> 02:58.310 The next operation in the pipeline is the filter method, which will perform the filtering as per the 02:58.550 --> 03:00.470 condition that we have provided here. 03:00.500 --> 03:02.960 Here we are performing the students. 03:03.980 --> 03:06.660 Grade level is greater than or equal to three. 03:06.680 --> 03:12.650 So here, from this step to this step, it will be passing the students one by one and the filter will 03:12.650 --> 03:14.450 be applied on top of it. 03:15.020 --> 03:21.200 If the student matches that filter, if this returns the boolean as true, then it will go to the next 03:21.200 --> 03:21.680 step. 03:23.000 --> 03:27.380 So after that we are performing again the filter operation. 03:27.380 --> 03:29.060 So it is similar to this step. 03:29.090 --> 03:31.400 It is going to get the sequence of students here. 03:31.400 --> 03:36.740 Basically, if you take a look at it in each and every step, we are getting the stream of students 03:36.740 --> 03:40.940 as an output of every operation in here. 03:40.970 --> 03:44.660 As I mentioned before, we are performing the filter operation. 03:44.660 --> 03:49.190 Again, there is no limit on the number of operations you can have. 03:49.220 --> 03:52.220 You can have n number of operations in here. 03:52.250 --> 03:58.190 The collect method is a one which converts the stream to the final desired output, which we are looking 03:58.190 --> 03:59.270 for here. 03:59.270 --> 04:04.040 We have used collectors dot to map which converts a stream to map. 04:04.040 --> 04:06.720 There are many variations available in this one too. 04:06.860 --> 04:12.770 You can have collectors dot to list or collectors dot to set, which I will be covering as part of the 04:12.770 --> 04:14.240 future tutorials. 04:14.690 --> 04:21.170 One key thing I would like to highlight here is that collect is the one which starts the complete process, 04:21.200 --> 04:24.570 meaning this is the one which starts the pipeline. 04:24.570 --> 04:31.350 If the collect method wasn't there, then there is no way this pipeline would have started and it wouldn't 04:31.350 --> 04:33.810 have created the output. 04:33.870 --> 04:37.710 All of the stream operation above won't happen at all. 04:37.710 --> 04:39.360 Let's go ahead and check this one. 04:39.360 --> 04:42.810 I'm going to go back to the example that we have coded in the previous tutorial. 04:43.550 --> 04:44.460 Back to IntelliJ. 04:44.640 --> 04:49.860 So in here, if I don't call this right, nothing will happen. 04:49.890 --> 04:51.300 Let's go ahead and check that. 04:51.450 --> 04:53.580 So it's going to give me all these errors. 04:53.580 --> 04:55.620 I'm going to comment this whole thing. 04:56.480 --> 05:01.790 And then what I'm going to do is I'm just going to copy until this line and then put it here. 05:03.090 --> 05:04.510 I'm going to run this one, too. 05:04.530 --> 05:09.720 So here, if I run the program, right, none of these operations would happen. 05:09.750 --> 05:10.530 I'm going to run it. 05:12.460 --> 05:12.940 So here. 05:12.940 --> 05:13.480 There you go. 05:13.480 --> 05:13.810 You see? 05:13.840 --> 05:14.380 Right. 05:14.410 --> 05:17.170 It did not start the stream process. 05:17.200 --> 05:20.470 It did not pass the students to this filter method. 05:20.470 --> 05:21.400 Nothing happens. 05:21.400 --> 05:24.490 Collect method is a one which starts the whole process. 05:24.490 --> 05:28.090 That is something which we have to register in your mind. 05:28.870 --> 05:33.870 So another important thing that we have learned here is that streams are lazy. 05:33.880 --> 05:40.300 No intermediate operations will be invoked until the terminal operation is invoked. 05:40.960 --> 05:48.380 So I'm going to remove the code, whatever we commented, and then let's write these things. 05:48.400 --> 05:53.410 So this one is going to give me a stream of students. 05:56.480 --> 05:57.410 And then. 05:59.810 --> 06:05.000 This one is again going to return stream of students, and this is the one which is going to give us 06:05.000 --> 06:06.620 the desired result. 06:06.890 --> 06:11.060 So type map, because that's what we are asking here. 06:11.960 --> 06:16.910 But this is all about Streams API and its internal working. 06:16.940 --> 06:21.710 Let's talk about some more features of the Streams API in the following tutorials. 06:21.740 --> 06:24.000 With this we came to the end of this tutorial. 06:24.020 --> 06:25.070 Thank you so much.