1 00:00:01,380 --> 00:00:04,530 So as we reach the end of this section, 2 00:00:04,530 --> 00:00:08,640 let's quickly review all the terminology around classes 3 00:00:08,640 --> 00:00:11,650 because there is so much different stuff going on. 4 00:00:11,650 --> 00:00:15,270 So a lot of different features that you can use. 5 00:00:15,270 --> 00:00:17,800 And since classes are probably the way 6 00:00:17,800 --> 00:00:21,230 you're gonna implement OOP by yourself, 7 00:00:21,230 --> 00:00:25,200 it's always good to have a nice overview of everything 8 00:00:25,200 --> 00:00:26,453 that we can do with them. 9 00:00:28,510 --> 00:00:30,950 So here we have a huge class, 10 00:00:30,950 --> 00:00:34,060 which essentially contains all the features 11 00:00:34,060 --> 00:00:37,740 that we studied over the last couple of lectures. 12 00:00:37,740 --> 00:00:41,370 So this is how we define a class. 13 00:00:41,370 --> 00:00:44,810 And in this case, it is actually a child class. 14 00:00:44,810 --> 00:00:49,810 So student is a child class of the parent class person 15 00:00:49,860 --> 00:00:53,550 and that is because here we are using the extends keyboard 16 00:00:53,550 --> 00:00:57,730 to set up the inheritance between these two classes. 17 00:00:57,730 --> 00:01:00,130 And remember that the extends keyword 18 00:01:00,130 --> 00:01:04,560 will also automatically set up the prototype chain for us. 19 00:01:04,560 --> 00:01:06,803 So we don't have to do anything manually. 20 00:01:07,670 --> 00:01:11,570 Next up, this is how we define a public field. 21 00:01:11,570 --> 00:01:14,920 So this is what we did in a very recent lecture. 22 00:01:14,920 --> 00:01:19,080 And so remember that a public field is very similar 23 00:01:19,080 --> 00:01:22,980 to just a property that we defined in a constructor. 24 00:01:22,980 --> 00:01:26,550 So it is available on every created object. 25 00:01:26,550 --> 00:01:29,793 So on every instance created by this class. 26 00:01:30,730 --> 00:01:33,750 Then of course, we also have private fields 27 00:01:33,750 --> 00:01:36,920 and they are almost the same as public fields, 28 00:01:36,920 --> 00:01:40,980 but they are not accessible outside of the class. 29 00:01:40,980 --> 00:01:42,920 And so therefore this is perfect 30 00:01:42,920 --> 00:01:47,080 for implementing data privacy and encapsulation. 31 00:01:47,080 --> 00:01:49,940 We also have static public fields. 32 00:01:49,940 --> 00:01:53,180 And so these are fields or like properties 33 00:01:53,180 --> 00:01:56,510 that are available only on the class. 34 00:01:56,510 --> 00:01:58,690 And I didn't show them to you in the code. 35 00:01:58,690 --> 00:02:00,830 So in one of the lectures, 36 00:02:00,830 --> 00:02:03,120 but this is how we can implement them. 37 00:02:03,120 --> 00:02:05,570 So just like static methods, 38 00:02:05,570 --> 00:02:10,223 we use the static keyword to make any field static as well. 39 00:02:11,160 --> 00:02:14,180 Then here, this is the constructor method 40 00:02:14,180 --> 00:02:17,400 and it is automatically called by the new operator 41 00:02:17,400 --> 00:02:20,790 whenever we create a new instance of the class. 42 00:02:20,790 --> 00:02:23,440 So basically a new object. 43 00:02:23,440 --> 00:02:26,380 And this constructor method is mandatory 44 00:02:26,380 --> 00:02:29,800 in any regular class, but it might be omitted 45 00:02:29,800 --> 00:02:33,870 in a child class if we want it to have the exact same number 46 00:02:33,870 --> 00:02:36,873 and the exact same name of parameters. 47 00:02:38,610 --> 00:02:42,390 Then inside of the constructor there is the call 48 00:02:42,390 --> 00:02:47,180 to the parent class and so that is the superclass. 49 00:02:47,180 --> 00:02:49,860 And this of course is only necessary 50 00:02:49,860 --> 00:02:52,920 whenever we are writing a child class. 51 00:02:52,920 --> 00:02:56,190 So when we're using the extent keyword. 52 00:02:56,190 --> 00:02:58,500 And remember that this one needs to happen 53 00:02:58,500 --> 00:03:02,023 before we access the disc keyword in the constructor. 54 00:03:03,790 --> 00:03:06,800 Then here we have an instance property. 55 00:03:06,800 --> 00:03:09,430 And so just like public fields, 56 00:03:09,430 --> 00:03:13,900 the property is also available on each created object. 57 00:03:13,900 --> 00:03:16,830 But the difference between this one and the public field 58 00:03:16,830 --> 00:03:19,610 is that we set these instance properties 59 00:03:19,610 --> 00:03:23,200 based on input data of the constructor. 60 00:03:23,200 --> 00:03:26,380 So basically these properties are more personalized 61 00:03:26,380 --> 00:03:30,410 and unique for each object while the fields are usually 62 00:03:30,410 --> 00:03:33,620 for something that is common to all the objects. 63 00:03:33,620 --> 00:03:37,230 For example, here at the university for all of the students 64 00:03:37,230 --> 00:03:39,540 is the University of Lisbon. 65 00:03:39,540 --> 00:03:43,653 And so that is not unique to each object, okay. 66 00:03:44,720 --> 00:03:48,750 Then here we are redefining a private field. 67 00:03:48,750 --> 00:03:51,790 And so this is what we did with the pin 68 00:03:51,790 --> 00:03:54,930 in the bank account example, right? 69 00:03:54,930 --> 00:03:59,780 So this private field should be unique for each student. 70 00:03:59,780 --> 00:04:02,760 And so we created the private fields out there 71 00:04:02,760 --> 00:04:04,180 without any value. 72 00:04:04,180 --> 00:04:07,760 And then here we are simply redefining it to the value 73 00:04:07,760 --> 00:04:09,833 that is coming into the constructor. 74 00:04:11,400 --> 00:04:15,313 Then here, as we already know, is a normal public method. 75 00:04:16,640 --> 00:04:19,680 Here, we are referencing a private field 76 00:04:19,680 --> 00:04:22,280 and also a private method. 77 00:04:22,280 --> 00:04:24,703 And so about the private methods, 78 00:04:24,703 --> 00:04:27,120 this is how they look like. 79 00:04:27,120 --> 00:04:28,440 But as I mentioned, 80 00:04:28,440 --> 00:04:31,800 they will probably not yet work in your browser. 81 00:04:31,800 --> 00:04:33,940 At least if you're watching this close 82 00:04:33,940 --> 00:04:36,520 to the recording date of this course. 83 00:04:36,520 --> 00:04:40,030 So as an alternative, you can fake private methods 84 00:04:40,030 --> 00:04:43,873 by using the underscore convention instead of the hash. 85 00:04:45,150 --> 00:04:49,270 Next up, this is what a getter method looks like. 86 00:04:49,270 --> 00:04:52,400 And remember that a getter method is basically 87 00:04:52,400 --> 00:04:55,540 so that we can get a value out of an object 88 00:04:55,540 --> 00:04:59,800 by simply writing a property instead of writing a method. 89 00:04:59,800 --> 00:05:02,860 So in this case, we could simply write student.testscore 90 00:05:04,094 --> 00:05:07,520 and that would then run this getter method 91 00:05:07,520 --> 00:05:10,480 and the same for the setter method. 92 00:05:10,480 --> 00:05:13,740 So in this case, we can simply define the test score 93 00:05:13,740 --> 00:05:15,910 by setting it to some value 94 00:05:15,910 --> 00:05:19,450 instead of calling a test score method. 95 00:05:19,450 --> 00:05:22,300 And keep in mind that if you have a setter 96 00:05:22,300 --> 00:05:26,500 for a property that is already defined in the constructor, 97 00:05:26,500 --> 00:05:29,830 then you need to create basically a new property 98 00:05:29,830 --> 00:05:32,530 with the underscore in front of it. 99 00:05:32,530 --> 00:05:35,570 So again, that is kind of a convention 100 00:05:35,570 --> 00:05:37,720 that you should use in this case. 101 00:05:37,720 --> 00:05:40,320 And then in the getter with the same name, 102 00:05:40,320 --> 00:05:44,190 you also need to then return that new property. 103 00:05:44,190 --> 00:05:46,580 So we did that in one of the lectures, 104 00:05:46,580 --> 00:05:49,690 when we did a name validation for the name 105 00:05:49,690 --> 00:05:52,270 that was passed into the constructor. 106 00:05:52,270 --> 00:05:53,103 Remember that? 107 00:05:54,940 --> 00:05:58,480 Next, this is how your write static methods 108 00:05:58,480 --> 00:06:02,700 and a static method is available only on the class. 109 00:06:02,700 --> 00:06:07,230 So it cannot access the instance properties nor the methods, 110 00:06:07,230 --> 00:06:08,873 but only the static ones. 111 00:06:09,710 --> 00:06:12,460 So for example, that static public fields 112 00:06:12,460 --> 00:06:14,530 that we defined there in the top 113 00:06:14,530 --> 00:06:18,190 will of course be accessible in the static method. 114 00:06:18,190 --> 00:06:20,950 And usually we use these static methods 115 00:06:20,950 --> 00:06:23,423 as helper methods for the class. 116 00:06:24,670 --> 00:06:28,450 Finally, this is how you then create a new object 117 00:06:28,450 --> 00:06:30,650 using the new operator. 118 00:06:30,650 --> 00:06:33,893 And so this should be nothing new at this point for you. 119 00:06:35,370 --> 00:06:37,580 Now, here's just a couple of things 120 00:06:37,580 --> 00:06:40,020 that we need to remember about classes 121 00:06:40,020 --> 00:06:43,550 and that I actually already mentioned before as well. 122 00:06:43,550 --> 00:06:46,750 So keep in mind that classes are really just 123 00:06:46,750 --> 00:06:50,250 syntactic sugar over constructor functions. 124 00:06:50,250 --> 00:06:55,250 Also classes are not hoisted, they are first class citizens 125 00:06:55,300 --> 00:06:59,930 and the class body is always executed in strict mode. 126 00:06:59,930 --> 00:07:02,870 Okay, and there you'll have it. 127 00:07:02,870 --> 00:07:06,110 This is an overview and also a summary 128 00:07:06,110 --> 00:07:09,593 of the entire syntax of classes in JavaScript.