WEBVTT 00:00.290 --> 00:00.860 Hi everyone. 00:00.860 --> 00:02.090 Welcome back to this tutorial. 00:02.090 --> 00:07.580 In this tutorial we will code and explore the function interface, which is part of the Java.util dot 00:07.640 --> 00:08.480 package. 00:08.480 --> 00:12.470 From the name it is clear that it stands for function. 00:12.500 --> 00:17.510 We all know that function in Java is nothing but a method in a class. 00:17.510 --> 00:26.330 So using function interface we can implement a functionality as like we code a method in Java and assign 00:26.330 --> 00:29.000 that functionality to a variable. 00:29.030 --> 00:35.090 This concept is really new in Java as a whole and this was never possible before. 00:35.090 --> 00:35.960 Java eight. 00:36.980 --> 00:43.190 Think about it again, coding a piece of logic and assigning it a variable and pass it across like any 00:43.190 --> 00:45.260 other object or variable. 00:45.260 --> 00:48.080 This is an excellent improvement in Java. 00:48.110 --> 00:51.140 Let's go ahead and explore that function interface. 00:53.650 --> 00:56.350 Step is I'm going to search for that function interface. 01:00.910 --> 01:07.270 And then if you take a look at the function interface, this got introduced as part of Java 1.8 and 01:07.270 --> 01:13.900 this one is part of the Java.util dot function package and it has one abstract method which is apply 01:13.900 --> 01:21.550 and it has two default methods, which is compose and and then now let's go ahead and explore this. 01:24.580 --> 01:30.010 Suppose I'm going to create a class called function example. 01:31.970 --> 01:35.960 And then I'm going to make this class executable. 01:35.990 --> 01:36.590 There we go. 01:36.620 --> 01:37.820 The class is ready. 01:37.850 --> 01:42.830 Now what I'm going to do, I'm going to create static. 01:44.290 --> 01:45.040 Function. 01:45.520 --> 01:50.920 So this function takes in an input and returns an output. 01:51.280 --> 01:53.770 So if you go ahead and open this function. 01:55.630 --> 01:56.620 Interface. 01:56.800 --> 01:58.690 It has one method called apply. 01:58.990 --> 02:02.020 It takes an input and it returns an output. 02:02.050 --> 02:09.260 But you have to pass two different types when you define the function interface. 02:09.290 --> 02:16.060 So what I'm going to do, I'm going to pass the input as a string and then I'm going to get the output 02:16.060 --> 02:17.230 also as a string. 02:17.900 --> 02:18.310 Okay. 02:18.340 --> 02:20.020 And then I'm going to assign this. 02:22.120 --> 02:24.940 What this particular function is going to do. 02:24.940 --> 02:27.010 I'm going to keep things really simple. 02:27.370 --> 02:28.810 This is going to. 02:30.470 --> 02:33.770 Your name and then it is going to perform. 02:35.700 --> 02:37.890 The uppercase operation on that string. 02:37.890 --> 02:44.070 So basically the input is going to be a string and then output is also going to be a string, but the 02:44.070 --> 02:51.570 output is going to be the uppercase version of the input that is being passed to this function interface. 02:51.690 --> 02:54.300 Now what I'm going to do, I'm going to use this. 02:56.250 --> 02:59.790 Result is what I'm going to do. 02:59.820 --> 03:02.430 I'm going to apply some input to it. 03:02.460 --> 03:10.800 So the method to use in order to pass the input to that particular function interface here is apply. 03:11.040 --> 03:13.050 Here we are going to pass Java eight. 03:13.470 --> 03:14.750 So what will be the output? 03:14.760 --> 03:19.140 The output is it is going to be the uppercase version of Java eight. 03:19.380 --> 03:21.480 As you see, the result is Java eight. 03:21.660 --> 03:28.950 Now what I'm going to do, I'm going to create one more function interface implementation, and then 03:28.950 --> 03:33.810 let's explore the and then method and compose method, which is part of the function interface. 03:33.810 --> 03:37.500 If we go and take a look at the function interface, there are two default methods. 03:37.530 --> 03:39.540 One is compose and next one is. 03:39.570 --> 03:40.200 And then. 03:41.790 --> 03:46.620 For that, I'm going to create one more instance of function interface. 03:46.620 --> 03:49.920 I'm going to name this one as add some string. 03:50.400 --> 03:51.600 Why do I name it like that? 03:51.600 --> 03:54.930 This is going to concat some string. 03:57.120 --> 04:00.150 So I'm going to name it as add some string. 04:00.390 --> 04:06.420 Basically, this is going to perform the uppercase operation and then add this default string to it. 04:08.170 --> 04:11.170 Now let's go ahead and explore the and then method. 04:13.030 --> 04:14.020 Copy this. 04:15.370 --> 04:18.670 Result of and then is. 04:20.010 --> 04:20.310 Here. 04:20.310 --> 04:26.640 I'm going to use the and then pass the add substring instance, then dot apply. 04:27.030 --> 04:31.770 Now if we take a look at it, it's going to get the input as Java eight. 04:31.980 --> 04:37.770 First it is going to perform the uppercase operation and then the result of that is going to be passed 04:37.770 --> 04:44.550 to this particular add some string function that is again going to perform the uppercase operation and 04:44.550 --> 04:49.050 then concat the result and print it in the console and run this. 04:51.730 --> 04:56.410 See it performed the uppercase operation first. 04:56.650 --> 05:01.450 That is the reason why you see this Java eight as a same string in here. 05:01.450 --> 05:05.570 And then the result of that is being passed to this function. 05:05.590 --> 05:12.610 Again, the uppercase operation is performed on the result of the first function result and then it 05:12.610 --> 05:16.270 added the default string to that one. 05:16.300 --> 05:18.340 Now let's explore. 05:21.110 --> 05:21.920 The compost method. 05:24.220 --> 05:24.730 Right. 05:24.730 --> 05:28.840 So this compost method, what it is going to do, it is going to. 05:30.400 --> 05:32.560 Execute this operation first. 05:32.590 --> 05:40.540 Basically, it is going to perform the uppercase operation and then it is going to concat the default 05:40.690 --> 05:43.960 and the result of that will be passed to this one. 05:44.050 --> 05:46.360 So the output is going to be. 05:48.010 --> 05:52.390 Java eight default, but everything will be in uppercase. 05:52.810 --> 05:54.190 Let's go ahead and execute this. 05:55.540 --> 05:56.380 There you go. 05:56.590 --> 06:05.080 So the difference between and then and compose is that and then executes the functions and the order 06:05.080 --> 06:06.100 it is mentioned. 06:06.550 --> 06:14.680 Compose is something which executes the first parameter function that is being passed to this compose. 06:15.520 --> 06:17.710 And then it executes the outer function. 06:18.430 --> 06:22.420 So that is some difference which you have to understand. 06:22.610 --> 06:26.650 So you can chain n number of and then s and n number of. 06:27.090 --> 06:29.620 I can do and then and pass another function. 06:30.650 --> 06:32.480 And I can do compose. 06:33.710 --> 06:36.690 You can do any number of and then and compose as part of it. 06:36.700 --> 06:38.470 And this concept is called. 06:40.180 --> 06:40.810 Chaining. 06:41.930 --> 06:44.450 Now, what are the advantages of this? 06:44.450 --> 06:44.720 Right? 06:44.750 --> 06:49.880 Now, I have this piece of functionality defined here, and if I want to use this functionality somewhere 06:49.880 --> 06:50.840 else in my code. 06:51.140 --> 06:58.400 Now to demonstrate that what I'm going to do, I'm going to create another class called function Example 06:58.400 --> 06:58.970 one. 06:59.750 --> 07:00.260 Okay. 07:00.260 --> 07:05.690 And then this is going to have a method called public static void main. 07:05.690 --> 07:07.100 And in here. 07:08.920 --> 07:14.140 I have the I have a method called public static void. 07:18.150 --> 07:18.570 String. 07:18.570 --> 07:20.460 So this method accepts a input called. 07:21.640 --> 07:23.280 String here. 07:26.120 --> 07:27.090 I didn't give the method. 07:27.090 --> 07:27.750 Name it. 07:31.310 --> 07:34.220 Concat it is going to perform the concat. 07:36.550 --> 07:38.260 And I'm going to call this. 07:40.620 --> 07:42.270 And parse a string called Hello. 07:45.980 --> 07:51.260 Now we want to concat the same default string to that one. 07:51.410 --> 07:56.930 In those kind of scenarios what you can do is since that particular. 07:58.810 --> 08:01.450 Function is defined in the static context. 08:01.990 --> 08:06.760 Gonna use that and then. 08:08.980 --> 08:14.140 Apply str the string that we are passing to this method. 08:17.090 --> 08:18.500 But this one returns a. 08:19.760 --> 08:20.570 String rate. 08:20.960 --> 08:23.600 String result equal to this. 08:25.270 --> 08:25.630 Perform. 08:25.630 --> 08:27.640 Concat is going to return that. 08:30.760 --> 08:32.280 Want to change our return type. 08:32.490 --> 08:34.830 Now we are going to print the result. 08:40.800 --> 08:42.750 Result and print the result. 08:47.130 --> 08:48.240 Now let's run it. 08:49.560 --> 08:49.980 There you go. 08:50.730 --> 08:52.200 We have hello. 08:52.200 --> 08:58.590 And then the default string added to that input that we have passed. 08:58.740 --> 09:01.950 So this is one of the benefit reusability again. 09:01.950 --> 09:05.550 So lambda expression is meant for reusability. 09:05.550 --> 09:08.070 And then one more thing is that. 09:09.490 --> 09:12.010 It's more readable, the code is more readable. 09:12.010 --> 09:17.470 And then you can, if you want to modify this or if you want to add some other functionality, then 09:17.470 --> 09:21.910 you can create a new function interface and you can reuse it throughout the code. 09:23.230 --> 09:25.120 So this we came to the end of this tutorial. 09:25.120 --> 09:31.240 In the next tutorial, we will explore the real world use case using the function interface.