WEBVTT 00:00.110 --> 00:00.650 Hi everyone. 00:00.650 --> 00:01.250 Welcome back. 00:01.250 --> 00:04.910 In this lecture we will look into some of the internals of constructors. 00:04.910 --> 00:10.100 And how can we apply domain validations before constructing this product instance. 00:10.130 --> 00:17.000 Because by default there are constructors generated by the compiler whenever you create a record class. 00:17.000 --> 00:22.610 And those constructors are called canonical constructors, because without the constructor there is 00:22.610 --> 00:25.160 no way we can create objects in Java. 00:25.190 --> 00:27.620 The concept is applicable for records too. 00:27.620 --> 00:32.840 So now in this case for the product, let's say when you are creating a product, you want to make sure 00:32.840 --> 00:39.230 the name is not null or the name is not blank, and the cost should be greater than zero, right. 00:39.230 --> 00:43.190 If you want to apply those kind of validations, what are the options we have? 00:43.220 --> 00:43.580 Now? 00:43.580 --> 00:46.190 Let's quickly jump into it and then explore those concepts. 00:46.190 --> 00:49.190 So the very first thing is we can apply those kind of validations. 00:49.190 --> 00:52.340 So what we need to do we just need to create a product. 00:52.340 --> 00:54.620 But this is not going to be a constructor. 00:54.650 --> 00:57.080 What this is going to be is a simple code block. 00:57.080 --> 01:03.210 So this code block has access to all the parameters that we pass to this specific record class. 01:03.210 --> 01:10.020 So in this case we can apply validations like if name not equal to null and and name is blank. 01:10.050 --> 01:13.440 If the name is blank we want to throw an illegal argument exception. 01:13.440 --> 01:13.800 Right. 01:13.800 --> 01:19.020 So in this case we can do throw new Illegalargumentexception. 01:19.020 --> 01:23.910 And the value is going to be name is not valid okay. 01:23.910 --> 01:25.350 So this is one exception. 01:25.380 --> 01:31.350 The other exception is we want to make sure the cost should not be zero or less than zero. 01:31.380 --> 01:32.370 In those kind of scenarios. 01:32.370 --> 01:39.240 What we can do in this case we can do if cost dot compare to because that's a function that we can use 01:39.240 --> 01:42.690 in order to compare the values that are part of the cost. 01:42.720 --> 01:43.200 Right. 01:43.200 --> 01:49.080 So in this case it can be bigdecimal dot zero is less than or equal to zero. 01:49.080 --> 01:55.050 So in this kind of scenarios we will make sure that the cost that's been passed to this product instance 01:55.080 --> 01:57.050 is always greater than zero. 01:57.080 --> 02:01.190 So in this case we also throw the illegal argument exception. 02:01.220 --> 02:01.640 Okay. 02:01.670 --> 02:04.010 But in this case it's going to be cast. 02:04.010 --> 02:05.810 Value is not valid. 02:05.990 --> 02:09.920 So these are the two validations that we have for the product record class. 02:09.920 --> 02:15.170 And this is how you can actually apply exceptions before constructing the object. 02:15.200 --> 02:16.970 Now let's go ahead and test this one. 02:16.970 --> 02:21.800 So what we are going to do we are going to be testing the name being not valid first. 02:21.800 --> 02:24.530 And then we will test the cast being not valid. 02:24.560 --> 02:28.250 So in this case I am going to name this one as name. 02:28.250 --> 02:29.630 Not valid. 02:29.840 --> 02:30.380 Okay. 02:30.410 --> 02:34.340 So in this case I'm going to pass the value as empty over here. 02:34.340 --> 02:39.230 And the way we are going to call this, it's going to be a little different because in JUnit five there 02:39.230 --> 02:40.910 is a handy way to test this one. 02:40.910 --> 02:44.870 So in this case what we are going to do we are going to call assert throws. 02:44.900 --> 02:47.900 So we are going to assert what that exception is thrown right. 02:47.930 --> 02:50.210 So in this case we can call assert throws. 02:50.210 --> 02:54.560 And then we can call out which exceptions we are expecting as part of this call. 02:54.590 --> 02:57.560 So in this case we are expecting an illegal argument exception. 02:57.590 --> 02:57.830 Right. 02:57.860 --> 03:00.290 So that's the exception which is thrown from here. 03:00.320 --> 03:03.950 Let's copy this one and then put it over here or dot class. 03:03.980 --> 03:04.340 Okay. 03:04.370 --> 03:06.590 And then what we do is we provide a supplier. 03:06.620 --> 03:10.310 So the way you provide the supplier is by providing a lambda right. 03:10.340 --> 03:12.890 So we are using the lambda syntax to provide the supplier. 03:12.920 --> 03:16.820 And then we can actually copy this one and then put this one over here. 03:16.850 --> 03:22.520 So what this is going to do is that when this code gets executed while we run this test case, this 03:22.520 --> 03:23.960 code is going to throw an exception. 03:23.960 --> 03:27.170 And that will be caught by this specific assert throws block. 03:27.170 --> 03:30.260 And that exception is going to be illegal argument exception. 03:30.260 --> 03:33.500 If there is a match then we will have access to that exception too. 03:33.530 --> 03:37.070 So the way we do it is by calling where exception. 03:37.100 --> 03:37.730 There you go. 03:38.360 --> 03:40.040 So in the then block what we can do. 03:40.070 --> 03:43.070 We can actually check what the actual message is. 03:43.070 --> 03:46.490 So in this case the message is going to be name is not valid. 03:46.520 --> 03:49.670 Let's copy it over here and then put it over here. 03:49.670 --> 03:54.720 And then we are going to be calling exception dot message. 03:54.720 --> 03:58.290 So this is how you test the exception scenario in JUnit five. 03:58.290 --> 04:01.710 So what we are doing is that we are calling the product record class. 04:01.710 --> 04:06.690 Basically we are creating an instance of the product record class, but we are passing the name as empty 04:06.720 --> 04:07.110 string. 04:07.110 --> 04:11.250 So in this case if the name is blank it's going to throw an illegal argument exception. 04:11.280 --> 04:13.080 Let's go ahead and execute this test case. 04:15.600 --> 04:16.110 There you go. 04:16.140 --> 04:17.010 The test case passed. 04:17.010 --> 04:19.560 So this means this is working as expected. 04:20.310 --> 04:24.000 Now the next step is to write a test case that's going to validate the cost right. 04:24.030 --> 04:28.140 So let's go ahead and copy this one and then create another test case. 04:28.140 --> 04:30.450 Let's name this one as cost not valid. 04:30.660 --> 04:33.180 So it's going to be cost not valid. 04:33.180 --> 04:37.890 And then in the place of this one this is going to be iPhone again which means we are passing a valid 04:37.890 --> 04:38.610 product name. 04:38.610 --> 04:40.920 But the value is going to be negative. 04:40.920 --> 04:49.890 So the cost represents -9.99999 which is not a valid value because we have a check over here that's 04:49.890 --> 04:56.330 going to throw an illegal argument exception in this case we can actually call cast is not valid. 04:56.360 --> 04:56.750 Okay. 04:56.780 --> 05:00.050 So now let's go ahead and execute this specific test case. 05:01.670 --> 05:02.060 There you go. 05:02.090 --> 05:03.710 This test case also passed. 05:03.740 --> 05:09.800 Now what I wanted to do I want to execute the whole test class to make sure that all the test cases 05:09.830 --> 05:11.630 are succeeding without any issues. 05:11.630 --> 05:15.920 So the introduction of these validations did not break the positive test case. 05:15.920 --> 05:21.890 So if we pass a valid name and the valid cast, then the test case is going to execute as expected. 05:21.920 --> 05:27.710 Now what I wanted to show you is that what are the options when it comes to creating a custom constructor. 05:27.710 --> 05:30.980 So let's assume the type is not something which is always known. 05:31.010 --> 05:36.680 If the type is not passed, then we would like to assign some generic type name like general, right. 05:36.680 --> 05:41.360 So if the type is not passed we would like to assign the type to be general, because in this case for 05:41.360 --> 05:44.360 iPhone we are passing the type as electronics, right. 05:44.360 --> 05:48.890 So from a product perspective we might not know the type all the time. 05:48.890 --> 05:50.720 So that's what this domain represents. 05:50.750 --> 05:51.170 Okay. 05:51.200 --> 05:55.970 So in this case what we will do is we will create the public and then provide the class name. 05:55.970 --> 05:58.790 And then we are going to be passing the name and cast. 05:58.790 --> 06:02.270 Because this is a mandatory value which will always be passed. 06:02.300 --> 06:02.660 Okay. 06:02.690 --> 06:08.990 And then when this happens if you take a look at the error over here, non-canonical record constructor 06:08.990 --> 06:11.030 must delegate to another constructor. 06:11.060 --> 06:15.830 What this means is that it needs to definitely call the canonical constructor. 06:15.830 --> 06:22.010 So in this case, the way you call it is by calling this dot or this name cast. 06:22.010 --> 06:25.880 And then we can assign the generic type as general. 06:26.210 --> 06:26.660 Okay. 06:26.660 --> 06:30.080 So this is how you create a custom constructor. 06:30.110 --> 06:34.190 Now let us go ahead and quickly write a test case to make sure this is going to work as expected. 06:34.190 --> 06:37.490 So in this case let's copy this one and then put it at the bottom. 06:38.180 --> 06:44.120 And we can name this one as create product custom constructor. 06:44.150 --> 06:44.480 Okay. 06:44.510 --> 06:46.310 And then I'm not going to pass the type right. 06:46.340 --> 06:51.330 So in this case this is going to make sure the call goes to the custom constructor that we created. 06:51.330 --> 06:53.040 So now the call goes to this one. 06:53.040 --> 06:59.340 But in the case of the type the type is going to be general because that's a default type that gets 06:59.340 --> 07:01.290 assigned if you don't pass a type. 07:01.290 --> 07:03.450 Now if I go ahead and execute this test case. 07:03.450 --> 07:06.330 So this is going to give me a green signal to there you go. 07:06.360 --> 07:08.490 So we got the green signal as expected. 07:08.490 --> 07:11.940 And if you take a look at the product the product type is assigned as general. 07:11.940 --> 07:16.380 And this particular code is being invoked by the this block. 07:16.380 --> 07:21.750 So any time you create a custom constructor, calling the canonical constructor using the this operator 07:21.750 --> 07:24.540 is a must, otherwise the compiler won't be happy. 07:24.570 --> 07:27.030 I hope you all had fun coding this. 07:27.030 --> 07:30.630 Custom validations and how to create custom constructors. 07:30.630 --> 07:32.850 So these are some of the advanced concepts. 07:32.850 --> 07:38.760 You will be actually implementing it for different use cases, but it is good to be aware that you have 07:38.760 --> 07:43.110 all these additional concepts that are available with record classes. 07:43.140 --> 07:44.430 This marks the end of this lecture. 07:44.430 --> 07:45.420 Thank you for watching.