WEBVTT 0 00:02.020 --> 00:06.740 Hi Everyone, welcome back to this tutorial. In this tutorial we are going to code a simple example to 1 00:06.740 --> 00:12.110 showcase the difference between the imperative style of programming and declarative style of programming. 2 00:12.370 --> 00:18.940 Use-case is perform the summation of 100 numbers from 0 to 100 and display the result. 3 00:19.130 --> 00:22.950 Let's go ahead and code this one. I have the IntelliJ open here. 4 00:22.970 --> 00:28.250 I don't want you guys to feel odd that I jumped in to the code directly without explaining about setting up the 5 00:28.250 --> 00:28.820 workspace. 6 00:28.820 --> 00:30.900 This is just for the demo purpose, 7 00:30.950 --> 00:33.290 that's the reason why I jumped into the code directly. 8 00:33.350 --> 00:38.700 We have a separate workspace set up section and the actual course is going to walk you through the project 9 00:38.700 --> 00:42.250 set up, creating classes step by step. 10 00:42.250 --> 00:44.230 Now let's go ahead and code this one. 11 00:44.230 --> 00:56.770 I'm going to create a class called Imperative versus Declarative example one and I'm going to make 12 00:56.770 --> 01:01.380 this classic executable by adding public static void main method. 13 01:01.500 --> 01:03.530 Let me put this in presentation mode. 14 01:03.700 --> 01:07.460 The first thing is we're going to code this use case using the imperative style. 15 01:08.140 --> 01:11.780 Let me give some code comments here so that we can differentiate between the two. 16 01:11.800 --> 01:14.020 This is the how style of programming ?. 17 01:16.910 --> 01:21.070 followed by that we are going to code the declarative style of programming. 18 01:25.970 --> 01:29.140 Basically this is the what style of programming. 19 01:30.170 --> 01:33.900 You'll be able to understand the difference between them by the end of this tutorial. 20 01:33.950 --> 01:39.660 Now the use case is to perform the summation of first hundred numbers from 0 to 100. 21 01:39.680 --> 01:43.380 I'm going to create a variable int sum=0; 22 01:43.580 --> 01:47.670 Basically I'm going to store the result in this sum int variable. 23 01:47.720 --> 01:52.270 Now I'm going to create a for loop int i=0; 24 01:52.280 --> 01:55.390 So we're going to perform the summation of the first hundred numbers. Right ? 25 01:55.390 --> 02:01.430 Now, we need to iterate for the first hundred times and the variable is going to be the value is going 26 02:01.430 --> 02:02.270 to be 100. 27 02:02.600 --> 02:06.530 Followed by that we're going to have the increment operator. 28 02:06.760 --> 02:13.970 So every time this loop iterates we are going to increase the sum by the i value. 29 02:14.120 --> 02:18.140 Now the final result is going to be. 30 02:18.260 --> 02:31.430 Sum using imperative approach. Going to be sum. Now lets run this program and check the result. 31 02:34.610 --> 02:39.370 So , the result is 5050. This is the how style of programming. 32 02:39.420 --> 02:47.370 Now I'm going to make use of the functions that got introduced as part of the Java8 in order to code 33 02:47.370 --> 02:48.490 the same use case. 34 02:48.630 --> 02:55.920 What I'm going to do is Intstream, there is a Intstream class that got introduced as part of Java 8 and 35 02:55.920 --> 03:01.440 then I'm going to give the range. The range is going to be zero to 100 . 36 03:01.660 --> 03:07.190 So when I give rangeClosed. Basically this is going to include the 100 value also. 37 03:08.130 --> 03:13.880 and then press Dot this is going to give you the access to the sum method. 38 03:14.520 --> 03:23.730 This sum method is going to give you the result which is the summation of all the values from 0 39 03:23.730 --> 03:24.710 to 100. 40 03:24.720 --> 03:28.560 Now I'm going to print this value here using declarative approach. 41 03:32.050 --> 03:32.540 approach. 42 03:32.550 --> 03:39.770 This is going to be sum1. Lets run this and check the result. There you go. It gave you the same result. 43 03:39.910 --> 03:48.130 Now let's compare this approach with this approach. let's start with the imperative approach. Here. 44 03:48.170 --> 03:50.830 we defined the summation needs to be done right. 45 03:50.910 --> 03:58.140 The first step is we declared a variable and then be we coded for loop and defined how many times 46 03:58.140 --> 04:05.370 this for loop needs to iterate and we explicitly increment the value of summation and get to the result. 47 04:05.400 --> 04:11.240 This is way we have been coding since the existence of Java and it has a lot of drawbacks to it. 48 04:11.280 --> 04:14.400 Like if you take a look at it we have a mutable variable. 49 04:14.400 --> 04:19.170 Here we are mutating the variables in order to get to the result. 50 04:19.350 --> 04:24.800 If we try to run this code in a multi-threaded environment we are going to have a lot of problem with 51 04:24.800 --> 04:25.740 this code. 52 04:25.770 --> 04:28.210 You might get unexpected results. 53 04:28.480 --> 04:34.560 And on the code readability perspective you need to go through the code line by line in order to understand 54 04:34.560 --> 04:35.740 what's happening. Here 55 04:35.750 --> 04:42.780 we have a simple logic but in reality some use cases can lead to make you write complex code. 56 04:42.780 --> 04:45.290 Now let's take a look at the declarative approach. 57 04:45.300 --> 04:51.390 This is what style of programming meaning you ask for what you want but you don't care about how the 58 04:51.390 --> 04:53.160 research is provided to you. 59 04:53.220 --> 04:54.500 If you take a look at the code. 60 04:54.500 --> 04:56.720 Here we have provided the range right. 61 04:56.730 --> 05:01.890 It performs something called internal iteration instead of the external iteration. 62 05:01.890 --> 05:08.010 If we compare this code with this code this performs ex-general iteration because we are explicitly 63 05:08.010 --> 05:17.070 iterating the for loop of from 0 to 100 range. It performs a summation behind the scenes and give you 64 05:17.070 --> 05:19.460 the result as soon as you call that sum method. 65 05:19.620 --> 05:24.660 But we don't have to worry about how would perform the summation behind the scenes. 66 05:24.720 --> 05:31.290 This piece of code will run us expected even in multi-threaded environment. Lets say you want to run this code 67 05:31.290 --> 05:32.840 in a multi threaded environment. 68 05:32.880 --> 05:37.950 Basically you have to create the threads and you have to start the thread in order to make this piece 69 05:37.950 --> 05:41.400 of logic to be run in a multi-threaded environment. 70 05:41.640 --> 05:48.250 But with this code if I have to run this code in a multi-threaded I just have to call the parallel 71 05:48.300 --> 05:48.860 in it. 72 05:48.870 --> 05:52.320 It splits the values which is a source Right?. 73 05:52.470 --> 05:58.080 It's splits the values and perform the summation and gives you the result. You might be wondering how many threads 74 05:58.080 --> 06:00.260 are created , how it works internally. 75 06:00.270 --> 06:05.340 All these concepts are covered in the course as part of the parallel programming section. 76 06:05.370 --> 06:11.310 It might be confusing now you just have to get into some hands on in order to be clear with these 77 06:11.310 --> 06:18.510 new classes and concepts. With this what I can say is that we can write better code with Java 8 features. 78 06:18.690 --> 06:23.170 We came to the end of the tutorial. Let's discuss another use case in the next tutorial. 79 06:23.190 --> 06:24.320 Thank you for watching.