WEBVTT 00:00.080 --> 00:00.590 Hi everyone. 00:00.590 --> 00:01.190 Welcome back. 00:01.190 --> 00:06.560 In this lecture we are going to learn about how to apply pattern matching on record classes. 00:06.560 --> 00:09.920 That's one of the reason why the name is called Record Patterns. 00:09.920 --> 00:14.060 Let me quickly explain the code that we are going to be exploring in this particular section. 00:14.060 --> 00:17.900 And then we'll go into experiment the record patterns in action. 00:17.900 --> 00:21.410 So the first thing is we have a animal seed interface. 00:21.410 --> 00:25.730 So this interface permits to classes which is cat and dog. 00:25.760 --> 00:29.000 The reason why I used interface is just to show the difference. 00:29.000 --> 00:33.110 You can use sealed with interfaces whenever it makes sense. 00:33.110 --> 00:38.300 It could be an abstract class also over here, but I just went ahead with the decision of using interface 00:38.330 --> 00:38.540 here. 00:38.570 --> 00:43.730 So in this case if you go and take a look at the cat class, this is a record class right. 00:43.730 --> 00:45.230 And then it has two properties. 00:45.230 --> 00:47.030 Number one is name and color. 00:47.030 --> 00:49.880 And then that implements the animal interface. 00:49.880 --> 00:52.250 And it's the same case for the dog one too. 00:52.280 --> 00:56.090 So the dog class also has two properties which is name and color. 00:56.090 --> 00:57.920 And that also implements animal. 00:57.920 --> 00:59.720 So the hierarchy makes sense here. 00:59.720 --> 01:02.480 And then if you open the animal service class. 01:02.480 --> 01:05.150 So in this case you will notice an implementation. 01:05.150 --> 01:09.630 So this is an implementation which is similar to what we saw in the previous lecture. 01:09.630 --> 01:11.730 So in this case this function accepts an animal. 01:11.730 --> 01:15.540 And then we have this enhanced switch to apply the pattern matching. 01:15.540 --> 01:18.210 So in this case if it's a null we return the empty string. 01:18.210 --> 01:21.720 If it's a cat type then we are going to be returning the name. 01:21.720 --> 01:23.100 So that's the name of this function. 01:23.100 --> 01:28.080 This function is going to get the animal type and then return the name for that particular animal type. 01:28.080 --> 01:30.930 So in the case of cat we create a binding variable. 01:30.930 --> 01:35.070 And then we use the binding variable to get the name and return that name. 01:35.070 --> 01:37.320 The same is applicable for the dog too. 01:37.350 --> 01:40.740 So this is very similar to what we saw in the previous lecture. 01:40.740 --> 01:45.120 So now what we are going to do is we are going to apply the record patterns for this one. 01:45.120 --> 01:46.170 So how do we do it. 01:46.200 --> 01:49.020 So in here what I'm going to do I'm going to create another function. 01:49.020 --> 01:51.930 So in this function I'm going to name this one as v two okay. 01:51.960 --> 01:59.220 So since it's a record class we know the record classes are basically data holders are immutable data 01:59.220 --> 01:59.910 containers. 01:59.940 --> 02:00.300 Right. 02:00.330 --> 02:03.930 So in this case what we are doing here is that we are just accessing the name. 02:04.170 --> 02:04.620 Right. 02:04.620 --> 02:06.930 We are not doing anything with the color at all. 02:06.930 --> 02:11.580 So in this case can we apply the pattern matching a level before. 02:11.580 --> 02:18.400 So in this case instead of creating an instance variable why not use the where name here and then where 02:18.430 --> 02:19.240 color here. 02:19.240 --> 02:23.500 So basically the idea is to extract the binding variable a level up. 02:23.530 --> 02:27.130 So in this case you don't have to use the instance variable to call the name. 02:27.130 --> 02:28.780 All you got to do is do this. 02:29.110 --> 02:30.430 That's all we need right. 02:30.430 --> 02:31.570 For the specific logic. 02:31.570 --> 02:33.970 So this is what Record Patterns is about. 02:33.970 --> 02:39.280 It's about taking it to the next level of matching and creating the binding variable in the case label 02:39.280 --> 02:39.640 itself. 02:39.640 --> 02:41.830 So in this case we can do the same thing for this one. 02:41.830 --> 02:44.230 So even here what we need is a name. 02:44.230 --> 02:46.120 Let's go ahead and return the name. 02:46.150 --> 02:46.810 There you go. 02:47.110 --> 02:50.410 So this code still compiles and works fine as expected. 02:50.410 --> 02:51.490 So what we will do. 02:51.490 --> 02:53.290 So there is a test case already available. 02:53.290 --> 02:53.890 There you go. 02:53.920 --> 02:55.210 Let me put this in the right. 02:56.020 --> 02:57.340 And in here what we are going to do. 02:57.370 --> 03:00.760 We are going to learn or write the test case for this function. 03:00.760 --> 03:02.800 So we have a retrieve name function here. 03:02.800 --> 03:04.300 And we have a test case for this one. 03:04.300 --> 03:07.900 And the test case is basically we are passing the input from this input function. 03:07.900 --> 03:11.050 So in the case of this one the name of the cat is going to be kitty. 03:11.080 --> 03:12.250 And the color is black. 03:12.250 --> 03:14.740 And the expected name is going to be kitty. 03:14.770 --> 03:15.100 Right. 03:15.130 --> 03:18.670 So because that's what this function returns, this function returns the name. 03:18.670 --> 03:21.190 And then we are performing the assertion over here. 03:21.190 --> 03:25.530 So we pass the animal and the expected value is going to be Kitty for this one. 03:25.530 --> 03:28.470 And we are asserting over here and similar for Scooby. 03:28.500 --> 03:30.720 The expected name is going to be Scooby. 03:30.720 --> 03:32.520 That's going to be returned from this function. 03:32.520 --> 03:37.440 So similar to this, what we are going to do, we are going to be writing the test case for the new 03:37.440 --> 03:40.650 function that we created using the record patterns approach. 03:40.650 --> 03:44.700 So in this case we can actually copy this one and then put it over here. 03:44.730 --> 03:48.930 And then in here we are going to be calling the retrieve name v2. 03:48.960 --> 03:54.240 So once you execute this function and if you get a green check mark, that means our code is working 03:54.240 --> 03:55.110 as expected. 03:55.140 --> 03:55.740 There you go. 03:55.770 --> 03:57.990 The code is working as expected. 03:57.990 --> 04:00.930 So we have three conditions that are being passed as an input. 04:00.960 --> 04:02.610 Number one is a cat type. 04:02.640 --> 04:05.610 Number two is a dog type, number three is a null type. 04:05.610 --> 04:09.270 And another thing that you notice here is that we don't have the default block here. 04:09.300 --> 04:16.080 The reason why we don't have a default block is because the animal has only two types of implementations. 04:16.080 --> 04:21.420 Number one is cat and dog, and we have the case label present for those two types. 04:21.420 --> 04:25.290 That's one of the reason the compiler isn't complaining about handling a default block. 04:25.290 --> 04:27.690 Since it's a record class, you don't need that. 04:27.690 --> 04:30.130 We covered that as part of the enhanced switch. 04:30.130 --> 04:34.630 If you have questions on this one, you can very well go back and watch the lecture that covers this 04:34.630 --> 04:37.000 exhaustive nature of the enhanced switch. 04:37.030 --> 04:41.650 Another thing that I want to call out is that the case null block I have it on the top right. 04:41.680 --> 04:43.390 It doesn't matter where you put it. 04:43.420 --> 04:45.070 You can just put the bottom two. 04:45.100 --> 04:47.320 The null will be handled as expected. 04:47.350 --> 04:49.960 Now let's go ahead and execute the test case one more time. 04:53.110 --> 04:53.590 There you go. 04:53.590 --> 04:55.210 We got the green check mark. 04:55.240 --> 04:56.470 As expected you see. 04:56.500 --> 04:56.800 Right. 04:56.830 --> 04:58.660 The null is handled as expected. 04:58.660 --> 05:04.090 So this is all about pattern matching on record classes which is also called record patterns. 05:04.090 --> 05:08.770 So in here we have this color binding variable created but it is not used right. 05:08.770 --> 05:12.280 There is an enhancement that's coming in the future part of the Java release. 05:12.280 --> 05:15.220 To not have this just to have something like this. 05:15.250 --> 05:20.860 So anytime you are going to not use a variable, you can have an underscore that is equivalent to a 05:20.860 --> 05:26.980 placeholder, not the actual variable, but it is not ready in Java 21 yet because that's the time I 05:27.010 --> 05:28.330 recorded this particular lecture. 05:28.330 --> 05:33.850 So for now you just need to deal with this redundant binding variable when you are doing record patterns. 05:33.850 --> 05:35.380 So this marks the end of this lecture. 05:35.380 --> 05:36.520 Thank you for watching.