WEBVTT 00:00.740 --> 00:01.340 Hi everyone. 00:01.340 --> 00:02.660 Welcome back to this tutorial. 00:02.660 --> 00:09.170 In this tutorial we will code a simple interface and then we will try to add default methods and static 00:09.170 --> 00:11.000 methods to that interface. 00:11.030 --> 00:14.300 The first step is I'm going to create an interface called multiply. 00:14.330 --> 00:21.080 That interface purpose is to perform the multiplication of the list that is being passed as an input. 00:22.120 --> 00:30.160 Want to create the interface in the class selection, I will change it to interface and then the interface 00:30.160 --> 00:31.630 name is going to be. 00:32.550 --> 00:33.450 Multiplier. 00:33.840 --> 00:34.380 There you go. 00:34.380 --> 00:36.120 We have the interface created. 00:36.150 --> 00:41.310 The next step is I'm going to create an implementation class of this interface. 00:41.310 --> 00:42.900 I'm going to create a class. 00:42.900 --> 00:46.380 The class name is going to be multiplier. 00:49.200 --> 00:53.670 And this is going to implement the multiplayer interface. 00:53.700 --> 00:54.330 There you go. 00:54.330 --> 00:57.510 We have the implementation class and interface ready. 00:57.540 --> 01:02.730 Now let's go ahead and introduce all the introduce all the new functionalities. 01:04.090 --> 01:05.200 So the first step is. 01:06.510 --> 01:08.370 Multiply is a method. 01:09.950 --> 01:14.630 It is going to perform the multiplication of the integer list. 01:15.170 --> 01:16.370 List of integer. 01:17.090 --> 01:19.340 I'm going to give it a name called Integer List. 01:20.790 --> 01:22.590 So this is a contract, right? 01:22.620 --> 01:25.800 We are not coding the default method and static method set. 01:25.830 --> 01:33.180 This multiplier has one single method called multiply, and then this is going to take in a input list 01:33.180 --> 01:36.030 and return the input as a int as an output. 01:36.060 --> 01:37.980 Now let's go back to the. 01:40.550 --> 01:45.110 Multiplier, which is the implementation class of this one. 01:45.140 --> 01:47.840 Now, we have a compilation issue here. 01:48.140 --> 01:49.910 Let's go ahead and check what's happening there. 01:50.580 --> 01:54.990 If you take a look at it, it is going to ask you to implement the method. 01:55.020 --> 01:55.770 There you go. 01:55.800 --> 01:58.950 So now we have to implement that method. 01:58.950 --> 02:05.250 As you see this override method, basically this means we are overriding something from this class. 02:05.430 --> 02:05.730 Okay? 02:05.730 --> 02:07.020 From this interface actually. 02:07.020 --> 02:12.180 So the interface has a multiply method and we are going to implement the logic how you want to perform 02:12.180 --> 02:13.410 the multiplication. 02:14.200 --> 02:16.720 Let's go ahead and perform the. 02:17.740 --> 02:18.970 Implementation logic. 02:19.510 --> 02:22.390 So in here I'm going to use the. 02:23.620 --> 02:24.610 Stream method. 02:25.920 --> 02:26.910 Dot stream. 02:27.240 --> 02:29.520 And then we are going to use a reduce method. 02:29.520 --> 02:35.910 If you remember from the prior tutorials, reduce method is handy in order to perform the. 02:36.990 --> 02:38.850 Multiplication operation. 02:38.940 --> 02:41.430 I'm going to do X, Asterix Y. 02:41.850 --> 02:47.670 So this is going to perform the multiplication of the input list and then return you the result. 02:48.060 --> 02:49.710 So I'm going to remove this return. 02:50.680 --> 02:53.350 And see what's happening here. 02:53.530 --> 02:59.950 It's going to give also, since we did not provide the default value, it is returning the optional. 02:59.950 --> 03:02.700 I'm going to have the default value as one. 03:02.710 --> 03:07.840 So whenever it performs the multiplication, it's going to start with one and then all the values that 03:07.840 --> 03:10.750 is being passed from the integer list. 03:10.780 --> 03:17.350 Now the next step is I'm going to create a client class that is going to call this implementation class 03:17.350 --> 03:18.940 and pass the input. 03:19.180 --> 03:20.080 Now. 03:21.610 --> 03:22.870 With another class. 03:23.470 --> 03:25.150 The class name is going to be. 03:26.770 --> 03:27.910 Multiplayer. 03:30.470 --> 03:30.850 Later. 03:33.930 --> 03:34.280 There you go. 03:34.290 --> 03:38.670 I'm going to make this class executable by adding public static void main method. 03:38.700 --> 03:41.760 Now the next step is I'm going to make this class. 03:42.330 --> 03:44.190 Let's put this in presentation mode. 03:46.190 --> 03:49.480 Now I'm going to create an instance of multiplayer. 03:49.490 --> 03:51.830 So multiplayer is a interface. 03:52.160 --> 03:59.300 I'm going to give it a name multiplayer and then new multiplayer, which is the implementation class. 03:59.300 --> 04:00.530 And this is allowed. 04:00.560 --> 04:02.300 Let's create the input list. 04:02.330 --> 04:08.360 List of integers and then it's going to be integer list. 04:10.920 --> 04:14.040 I'm going to keep this example really simple. 04:14.280 --> 04:17.780 I'm going to use arrays dot as list. 04:17.880 --> 04:22.110 I'm going to give the values as one comma, three, comma five. 04:22.140 --> 04:24.330 So the result is going to be 15. 04:24.360 --> 04:28.950 That's the result which this multiplayer implementation class is going to return. 04:28.980 --> 04:30.510 Now let's call this. 04:32.530 --> 04:40.960 So the result is you're going to call the multiplier, you're going to use the multiplier instance dot 04:40.960 --> 04:41.630 multiply. 04:41.650 --> 04:47.180 There you see, this is a method which we implemented in the multiplier class. 04:47.200 --> 04:49.660 Now I'm going to pass this integer list. 04:50.260 --> 04:51.970 Let's run this and check the result. 04:54.790 --> 04:55.150 There you go. 04:55.150 --> 04:57.420 It gave you the result as 15. 04:57.430 --> 04:59.640 So nothing new until this point. 04:59.650 --> 05:03.700 This is something which you can do it before Java eight also. 05:03.700 --> 05:08.800 Now let's start introducing the default method and static methods. 05:08.800 --> 05:11.320 So default methods what I'm going to do. 05:12.290 --> 05:17.280 I'm going to go to this multiplayer interface, so I'm going to do this in here. 05:17.290 --> 05:25.580 I'm going to create a method called size that is going to give you the size of the input list. 05:25.600 --> 05:27.010 That's what it is going to do. 05:27.100 --> 05:30.720 What I'm going to do, I'm going to create the default method. 05:30.730 --> 05:35.950 The first step is we are going to have the default keyword and then what is that? 05:35.950 --> 05:36.820 It is going to return. 05:36.820 --> 05:39.820 It is going to return the size of the input list. 05:40.180 --> 05:44.140 So the size of the input list is going to be an integer. 05:44.140 --> 05:46.930 And then if the size method. 05:46.930 --> 05:51.970 So I'm creating this size method in the multiplayer interface. 05:51.970 --> 05:54.760 So this is going to accept the list of. 05:55.670 --> 05:56.510 Integer. 05:58.860 --> 05:59.900 Want to give it a name? 06:00.750 --> 06:01.500 And what is that? 06:01.500 --> 06:02.490 It is going to return. 06:02.490 --> 06:04.440 This is going to return. 06:07.290 --> 06:08.280 Integer list. 06:08.280 --> 06:09.450 Dot size. 06:11.430 --> 06:13.530 Okay, we're good, right? 06:13.530 --> 06:19.830 So we have successfully implemented the default method in the interface. 06:20.130 --> 06:21.930 Now how can we call that? 06:24.510 --> 06:28.620 So when to have this code command as a default method. 06:31.460 --> 06:33.350 Now, remember? 06:34.500 --> 06:36.650 Can use the same multiplayer interface when we call. 06:36.680 --> 06:40.250 Before we just had the multiply method, right? 06:40.280 --> 06:43.400 Now let's see, what are the other what are the methods that are available? 06:45.020 --> 06:45.750 We take a look at it. 06:45.770 --> 06:48.500 It has another method called size. 06:48.920 --> 06:51.500 So this is a method which we just coded. 06:51.800 --> 06:55.670 I'm going to call that method and then I'm going to pass this integer list. 06:56.840 --> 06:57.260 Good. 06:57.260 --> 06:58.910 Now let's go ahead and run this one. 07:00.830 --> 07:03.660 We take a look at it, it returned you the result as three. 07:03.680 --> 07:08.570 So if you compare this with the prior Java eight version. 07:09.980 --> 07:11.200 Let's go back to the interface. 07:11.210 --> 07:14.380 In the interface, we have introduced this new functionality. 07:14.390 --> 07:17.180 This was never possible before Java eight. 07:17.210 --> 07:22.850 Basically, you could have created another, you could have declared another method called sys, but 07:22.880 --> 07:28.940 the impact would be you have to go to the multiplayer implementation class and then implement the logic. 07:28.940 --> 07:36.620 So the logic, whatever we had implemented here in the interface needs to be implemented only in multiplayer 07:37.130 --> 07:38.810 class prior to Java eight. 07:38.840 --> 07:41.420 So that's the advantage of default methods. 07:41.420 --> 07:47.720 We can still add functionalities to the list interface, which is the multiplayer, not the list interface, 07:47.720 --> 07:54.680 the multiplayer interface and not affecting any of the classes that already implements this interface. 07:54.830 --> 07:58.820 This is one handy way of enhancing an interface. 07:58.820 --> 08:01.400 Now let's talk about the static methods. 08:01.400 --> 08:05.090 So I'm going to create another method called static. 08:05.850 --> 08:10.980 And then this method is going to return me a boolean if the list is not empty. 08:11.490 --> 08:12.760 That's what it is going to do. 08:12.780 --> 08:19.680 So I'm going to create a method called is empty and this is going to accept a list of. 08:20.350 --> 08:21.070 Integer. 08:21.820 --> 08:22.200 Okay. 08:22.210 --> 08:24.130 I'll give it a name integer list. 08:24.340 --> 08:25.270 So what is that? 08:25.270 --> 08:26.200 It is going to return. 08:26.200 --> 08:28.000 This is going to return. 08:28.810 --> 08:32.650 If the integer list is not null. 08:34.260 --> 08:35.070 And. 08:36.420 --> 08:38.760 Integer less dot size. 08:41.930 --> 08:42.860 Equal to equal to zero. 08:42.860 --> 08:46.510 Basically, this is going to size greater than zero, right? 08:47.360 --> 08:52.250 So if the list is empty, then this will return false. 08:52.250 --> 08:55.220 If the list is not empty, then this will return. 08:55.340 --> 08:56.000 True. 08:56.390 --> 08:58.490 Now, let's go ahead and check it. 08:59.220 --> 09:02.970 Let's try to access the new static method using the. 09:03.420 --> 09:04.890 Multiplayer instance. 09:05.700 --> 09:08.720 You see the isEmpty method here? 09:08.900 --> 09:11.000 No, because it's a static method. 09:11.000 --> 09:15.490 You can only access a static method using the class. 09:15.500 --> 09:16.100 Right. 09:16.130 --> 09:23.720 Basically in here, using the interface, I'm going to give the comment as static method is empty is. 09:24.770 --> 09:29.260 And we are going to use the interface itself because it's a static method. 09:29.270 --> 09:31.760 You can only access the static method using the. 09:32.770 --> 09:34.180 Actual interface itself. 09:34.180 --> 09:37.450 And then you get access to that use empty method. 09:38.340 --> 09:39.530 And let's pass this one. 09:39.540 --> 09:43.720 So this is going to return the value as true because it checks the implement. 09:43.740 --> 09:48.790 If we take a look at the implementation, it checks the integer is not equal to null and an integer 09:48.790 --> 09:50.550 list dot size greater than zero. 09:51.200 --> 09:53.930 But our input list, if you take a look at it, has three elements. 09:53.930 --> 09:56.660 So we are going to get the result as true. 09:58.100 --> 09:58.530 Here you go. 09:58.550 --> 10:00.260 It gave you the result as true. 10:01.110 --> 10:01.470 Right. 10:01.470 --> 10:04.310 So let's go ahead and go back to the interface. 10:04.320 --> 10:06.330 What is the difference between the two in that case? 10:06.330 --> 10:06.990 Right. 10:08.770 --> 10:15.070 If you remember from the presentation, default methods can be overridden, but the static methods. 10:15.790 --> 10:17.030 Cannot be overwritten. 10:17.050 --> 10:22.670 Now the implementation class of the multiplayer interface is multiplayer. 10:23.220 --> 10:25.150 I'm going to open the class. 10:25.180 --> 10:32.230 I'm going to copy this method, and then I'm going to go to the multiplayer class, as you see here. 10:33.080 --> 10:35.840 And then I'm going to overwrite that functionality. 10:36.530 --> 10:40.180 You cannot use default methods in the context of a class. 10:40.230 --> 10:42.980 So I'm going to give it a access modifier. 10:42.980 --> 10:51.790 And then the functionality is similar to the multiplier interface, but we are overriding it, right? 10:51.800 --> 10:55.460 In order to show the difference what I'm going to do, I'm going to add a sort. 10:56.420 --> 10:59.540 Want to give the code commands as inside. 11:00.820 --> 11:02.020 Multiplier. 11:03.210 --> 11:04.200 Interface. 11:05.400 --> 11:06.570 I'm going to copy it. 11:06.750 --> 11:09.640 I'm going to go back to the multiplayer pool. 11:10.660 --> 11:11.500 In here. 11:11.500 --> 11:16.180 I'm going to give inside multiplier class. 11:17.190 --> 11:20.640 Just to show the difference between which method is getting invoked. 11:20.640 --> 11:26.970 So basically what we have done here, we have the multiplayer interface, which has the default method, 11:26.970 --> 11:31.790 and then we are trying to override the similar functionality. 11:31.800 --> 11:37.860 You should match the method signature, meaning the parameters, the return type and the method name 11:37.860 --> 11:39.390 should all be the same. 11:39.390 --> 11:43.080 That's what we have here in the multiplayer class. 11:43.110 --> 11:48.390 Now we will call the size method and then see which. 11:49.460 --> 11:51.080 Implementation gets invoked. 11:51.890 --> 11:52.310 Right. 11:52.430 --> 11:55.580 I'm going to go to the multiplayer client class. 11:56.890 --> 11:58.150 Multiplayer client. 11:58.180 --> 11:58.900 There you go. 11:59.200 --> 12:01.670 Let's run this and check the result. 12:01.690 --> 12:10.600 So the size method is going to invoke either the method implementation in the interface or the implementation 12:10.600 --> 12:11.170 class. 12:11.500 --> 12:13.000 Let's run this and check the result. 12:13.300 --> 12:21.820 If you take a look at the result it implemented inside multiplier class, so on runtime, when it is 12:21.820 --> 12:29.560 trying to resolve the method, it resolves the multipliers multiplier plus size method. 12:29.590 --> 12:36.340 That's the one of that's one of the key feature that you have to keep in your mind whenever you override 12:36.340 --> 12:37.380 a default method. 12:37.390 --> 12:43.990 Then the the class that overrides that functionality is the one which is going to get invoked. 12:45.320 --> 12:48.890 So let's go back to the difference between the default and static methods. 12:48.920 --> 12:49.760 Static methods. 12:49.760 --> 12:53.900 We cannot override it because this is at the class level. 12:53.930 --> 12:59.750 Basically, in order to access this method, we use the interface and then we will call the isEmpty 12:59.750 --> 13:00.380 method. 13:00.950 --> 13:05.120 Okay, so this is something which we have to be really, really careful about. 13:05.150 --> 13:14.990 Whenever you implement the same default method in the implementation class, then that is going to take 13:14.990 --> 13:17.150 the precedence and during runtime. 13:18.220 --> 13:19.780 That is going to get invoked. 13:21.430 --> 13:21.730 With this. 13:21.730 --> 13:23.150 We came to the end of this tutorial. 13:23.170 --> 13:24.190 Thank you for watching.