WEBVTT 00:00.650 --> 00:06.830 So next up we are going to learn about the inheritance and polymorphism. 00:08.180 --> 00:10.730 So we've got a person class already. 00:11.300 --> 00:16.880 Now let's create another class that would be based on this person class. 00:16.880 --> 00:18.830 This is called inheritance. 00:18.980 --> 00:23.090 I am defining a class that will be called employee. 00:23.660 --> 00:31.820 I use the keyword extends to tell PHP that this class is based on person. 00:32.450 --> 00:41.360 So that's inheritance because it inherits all the fields and all the methods of the parent class, but 00:41.360 --> 00:43.940 it can add something on its own. 00:44.210 --> 00:49.580 Now let me copy the constructor from the person to the employee. 00:51.110 --> 00:56.150 And we are doing this because I'd like to add another fields in here. 00:56.150 --> 01:00.230 So this would be a string called position. 01:01.730 --> 01:05.330 So employee has position at work. 01:05.960 --> 01:13.760 Okay, now I'd like the message for the employee to be a little different than the one from person. 01:13.790 --> 01:21.200 Additionally, when introducing an employee, I'd like to know what's the position of an employee? 01:21.260 --> 01:30.080 Now I can create an employee right now by using new employee. 01:30.110 --> 01:32.180 I can pass the name. 01:33.950 --> 01:39.860 I can pass the age and I can pass the position. 01:39.920 --> 01:43.700 Let's say that that's a manager. 01:45.440 --> 01:51.110 Now, when I echo the employee introduce method. 01:52.220 --> 01:54.620 This should all work fine. 01:55.520 --> 01:58.010 So I'm Jerry and I'm 45 years old. 01:58.040 --> 02:02.150 This is matching the data that we've passed to the employee class. 02:02.780 --> 02:10.970 So the things that we should learn in here is that the employee has all the data and all the methods 02:10.970 --> 02:12.530 of the base class. 02:12.530 --> 02:14.720 So person is the base class. 02:14.750 --> 02:18.110 This method is only defined in the person class. 02:18.110 --> 02:25.310 Yet when we create an employee which extends person, we can call this method. 02:27.800 --> 02:35.210 Now in our case, using this introduce method from the base class is not ideal because the base class 02:35.240 --> 02:39.590 does not know about the position, it's only about the person. 02:39.590 --> 02:45.680 So when introducing an employee, it's still only going to mention the name and the age. 02:46.340 --> 02:50.630 So what we can do is we can overwrite this method. 02:50.630 --> 02:51.500 That's important. 02:51.500 --> 02:53.240 Word overriding. 02:53.810 --> 03:01.850 Overriding means we redefine the method that's specific for an employee. 03:03.140 --> 03:13.860 And now I can say I work as a this position. 03:16.440 --> 03:17.190 Dot. 03:18.120 --> 03:18.960 Now. 03:21.570 --> 03:24.990 Let's see how the message will look like right now. 03:24.990 --> 03:29.130 By the way, let me concatenate that with a new line. 03:29.790 --> 03:31.680 Okay, let's run this. 03:32.130 --> 03:34.590 I work as a manager. 03:34.770 --> 03:35.190 Mm. 03:35.730 --> 03:39.750 So we've got the information that we wanted to convey. 03:39.750 --> 03:44.910 We state the position, but we are losing the previous behavior. 03:44.910 --> 03:52.410 So it might look like we are actually doing something that doesn't really benefit us. 03:52.440 --> 03:54.870 And to fix this. 04:01.560 --> 04:11.160 We just need to make sure we are also using the base class method and to access inside the classes the 04:11.160 --> 04:14.310 methods or data from the parent class. 04:14.340 --> 04:23.400 We use the special parent syntax double colon, and that way I can call the introduce method from the 04:23.400 --> 04:26.580 parent, which should just output the text. 04:28.800 --> 04:31.260 That introduces the person. 04:31.740 --> 04:38.580 And I can add a space here so we can concatenate that with our own more specific implementation. 04:38.580 --> 04:46.710 So now when I run this we've got the base introduction plus the position. 04:49.380 --> 04:49.650 Okay. 04:49.650 --> 04:53.460 So now let's see an example of polymorphism. 04:54.150 --> 04:56.790 Instead of just one variable. 04:57.240 --> 05:01.020 Let's define an array of people. 05:03.180 --> 05:07.830 Now the first element in this array would be our employee Jerry. 05:09.090 --> 05:14.400 But we're also going to have a person, just a person that doesn't work anywhere. 05:14.970 --> 05:15.930 That would be me. 05:18.300 --> 05:21.480 So we can still use this person class. 05:21.960 --> 05:33.060 Now let me define a function that will be called introduce and it accepts an argument of type person. 05:35.640 --> 05:42.660 Now, thanks to polymorphism, when we have a common parent class, we can treat objects of different 05:42.660 --> 05:46.620 classes as if they are the same parent class. 05:46.860 --> 06:00.060 So in case of this simple method, I can do echo person introduce and I concatenate that with a new 06:00.060 --> 06:00.810 line. 06:00.840 --> 06:08.640 Now let's also change the name of this variable to people not employees because it contains different 06:08.650 --> 06:12.460 classes, but they all have the same base class. 06:12.490 --> 06:16.600 Now, in the script I'm just going to do for each. 06:18.610 --> 06:21.550 People as person. 06:22.510 --> 06:29.230 And I will just call the introduce function, which accepts an object of class person. 06:29.230 --> 06:37.480 And with polymorphism, actually both the employee and person can be treated as if they are the person 06:37.480 --> 06:45.790 class, because the object which is of class person is actually of this specific class, and the employee 06:45.820 --> 06:50.410 extends the person, which means it will have the introduce method. 06:50.410 --> 06:51.490 For example. 06:51.490 --> 06:54.970 So I can call introduce passing the person. 06:54.970 --> 06:56.080 Now let's run this. 06:56.080 --> 07:02.350 And those objects have their specific implementation of the introduce method with Jerry. 07:02.380 --> 07:05.410 This will add his position. 07:05.470 --> 07:10.270 Now with me it's only saying that I'm pure and I'm 37 Seven. 07:11.230 --> 07:17.470 Now, at this point, I'd like you to appreciate how important polymorphism is. 07:17.710 --> 07:25.780 Now, what you see here is we've created a function that accepts an argument, and you've just seen 07:25.780 --> 07:32.290 us passing objects of different classes, yet everything has worked perfectly. 07:32.290 --> 07:39.190 And the same method could be run for different objects, yet it yielded different results. 07:39.190 --> 07:47.500 So that is the power of polymorphism that you can create code that doesn't have to change if some specific 07:47.500 --> 07:50.890 implementation on your classes changes. 07:51.580 --> 07:57.190 So we just have a base class which has some base methods and we can depend on that. 07:57.190 --> 08:06.040 And if we then decide to add more classes like a boss class or a director class, this code does not 08:06.040 --> 08:06.760 have to change. 08:06.760 --> 08:11.890 It will still function and it will still properly introduce everyone.