1
00:00:01,280 --> 00:00:06,710
‫In this and the next videos you are going to learn about interfaces and they are quite important because

2
00:00:06,710 --> 00:00:12,890
‫they really extend the functionality of object oriented programming and of classes.

3
00:00:13,010 --> 00:00:15,140
‫So what is an interface?

4
00:00:15,170 --> 00:00:22,490
‫Well, think of interfaces as contracts, where a class that implements an interface agrees to provide

5
00:00:22,490 --> 00:00:25,940
‫implementations for all objects defined by that interface.

6
00:00:26,180 --> 00:00:33,500
‫This means an interface will contain the contract terms, methods and properties, but how we implement

7
00:00:33,500 --> 00:00:36,890
‫them is up to the class that implements the interface.

8
00:00:36,950 --> 00:00:42,800
‫As long as these interface methods are implemented in our class, the interface will remain happy.

9
00:00:43,580 --> 00:00:47,150
‫So interfaces cannot contain any implementations.

10
00:00:47,150 --> 00:00:48,110
‫That's important.

11
00:00:48,170 --> 00:00:54,630
‫So their names are generally prefixed with the IE to distinguish them from other sharp objects.

12
00:00:54,650 --> 00:00:58,520
‫We create interfaces using the interface keyword.

13
00:00:58,670 --> 00:01:01,790
‫Now let's look at how we can do that in practice.

14
00:01:02,640 --> 00:01:02,940
‫All right.

15
00:01:02,940 --> 00:01:05,410
‫So we there we are back in Visual Studio.

16
00:01:05,430 --> 00:01:12,040
‫So one of the most used functionalities in RC Sharp classes is comparing to instances of a class.

17
00:01:12,060 --> 00:01:14,370
‫This is done using the equals method.

18
00:01:14,400 --> 00:01:18,990
‫This will compare to see if the reference to both of the classes is the same.

19
00:01:19,080 --> 00:01:25,230
‫However, we want to compare them and see if they are equal based on some other fields.

20
00:01:25,440 --> 00:01:30,930
‫So we can achieve this by implementing an interface called I Equitable.

21
00:01:31,110 --> 00:01:38,600
‫So in our case, we have a class called Ticket and it defines one property called duration in hours.

22
00:01:38,610 --> 00:01:41,160
‫So let's go ahead and create this class real quick.

23
00:01:41,310 --> 00:01:47,820
‫Here I have a new class and actually I can either go here or use the shortcut control K and C and I'm

24
00:01:47,820 --> 00:01:49,530
‫going to call this one ticket.

25
00:01:49,980 --> 00:01:54,660
‫So this ticket, as I said, just has one property and a constructor.

26
00:01:54,660 --> 00:01:56,010
‫So let's put them in here.

27
00:01:56,020 --> 00:01:59,940
‫So this property is there to store the duration of the ticket and ours.

28
00:01:59,940 --> 00:02:03,180
‫And then we have the constructor here.

29
00:02:04,230 --> 00:02:08,460
‫And now let's go ahead and implement the AI equitable interface.

30
00:02:08,640 --> 00:02:16,320
‫So therefore we use something similar to what we did when using inheritance, we use the colon and then

31
00:02:16,320 --> 00:02:17,970
‫the interface that we want to use.

32
00:02:17,970 --> 00:02:19,800
‫And you see there are a bunch of them.

33
00:02:20,070 --> 00:02:23,700
‫And the one that I want to use is going to be the high equitable.

34
00:02:24,000 --> 00:02:29,030
‫Now you need to define of what type of objects you want to compare.

35
00:02:29,040 --> 00:02:32,250
‫So here I want to compare tickets to each other.

36
00:02:32,430 --> 00:02:34,960
‫This is why I need to add the ticket keyword.

37
00:02:34,980 --> 00:02:42,300
‫Now you will notice that Visual Studio isn't very happy because it says defines a generalized method

38
00:02:42,300 --> 00:02:46,110
‫that a value type or class implements to create a specific method.

39
00:02:46,110 --> 00:02:51,720
‫But then the problem that we get here is ticket does not implement interface members I equitable ticket

40
00:02:51,720 --> 00:02:52,500
‫equals ticket.

41
00:02:53,500 --> 00:02:58,590
‫We can very easily fix that by just going ahead and implementing this.

42
00:02:58,600 --> 00:03:04,790
‫So we could have either used all members well to implement them explicitly or we can just do it manually.

43
00:03:04,810 --> 00:03:06,000
‫Let's do that real quick.

44
00:03:06,010 --> 00:03:14,470
‫So basically I want to return a boolean that will check if whatever ticket I'm passing, which will

45
00:03:14,470 --> 00:03:19,000
‫be the other ticket, is going to be the same as the ticket.

46
00:03:19,000 --> 00:03:21,070
‫That is the one that calls this method.

47
00:03:21,340 --> 00:03:22,330
‫So the ticket.

48
00:03:23,110 --> 00:03:28,990
‫That we create out of this, we compare it to another ticket, and then we want to compare the duration

49
00:03:28,990 --> 00:03:29,260
‫hours.

50
00:03:29,260 --> 00:03:33,100
‫So if they have the same duration, then we will assume that they are the same ticket.

51
00:03:33,730 --> 00:03:41,590
‫So here we can just go ahead and return the comparison of this duration in hours compared to the other

52
00:03:41,590 --> 00:03:43,000
‫duration in hours.

53
00:03:43,030 --> 00:03:49,390
‫So basically we're saying this ticket has a duration in hours and the other ticket is also of type ticket.

54
00:03:49,390 --> 00:03:53,290
‫So it has a duration in hours and we're comparing the two with each other.

55
00:03:53,290 --> 00:03:59,530
‫And this comparison, this double equal sign, will basically return true or false?

56
00:04:00,040 --> 00:04:02,950
‫So this is Boolean operator in left and right.

57
00:04:02,950 --> 00:04:07,060
‫So what it does is it compares what is left to it, to what is right to it.

58
00:04:07,060 --> 00:04:10,000
‫And if they are the same, then it will return true.

59
00:04:10,030 --> 00:04:11,740
‫Otherwise it will return false.

60
00:04:11,740 --> 00:04:15,250
‫Basically saying that this method equals will return true.

61
00:04:15,250 --> 00:04:22,060
‫If the ticket that calls the equals method has the same duration in hours as the ticket that we compare

62
00:04:22,060 --> 00:04:23,830
‫it with, then return true.

63
00:04:23,830 --> 00:04:25,480
‫If not, then return false.

64
00:04:26,220 --> 00:04:30,330
‫Okay, so let's go over to our program, CSE, and actually use this.

65
00:04:30,340 --> 00:04:37,840
‫So here what we're going to create is two tickets, one will be TW one and it will be a new ticket and

66
00:04:37,840 --> 00:04:40,210
‫it will have a duration in hours of ten.

67
00:04:40,210 --> 00:04:47,560
‫And then let's actually copy this and create a ticket two, which will also have 10 hours and now we

68
00:04:47,560 --> 00:04:48,580
‫can compare them.

69
00:04:48,580 --> 00:04:59,050
‫So here let's use control right line to just display tw two dot equals and compare tw one with it.

70
00:04:59,050 --> 00:05:06,400
‫So here I'm basically comparing our ticket two to our ticket one and comparing it using the equals method.

71
00:05:06,880 --> 00:05:08,440
‫Now let's run this real quick.

72
00:05:09,820 --> 00:05:11,920
‫And you will see that it says true.

73
00:05:12,160 --> 00:05:17,710
‫And that is usually not the case for the equals method, because if you compare two objects using a

74
00:05:17,710 --> 00:05:19,480
‫normal equals method, so to speak.

75
00:05:19,510 --> 00:05:25,360
‫So if we were not to implement this, let's get rid of this here for a second.

76
00:05:25,840 --> 00:05:29,830
‫So let's comment all of this out and let's compare the two.

77
00:05:29,860 --> 00:05:31,690
‫You see, the method still is there.

78
00:05:32,500 --> 00:05:37,900
‫This equals still works, because equals is a method that exists in general.

79
00:05:37,900 --> 00:05:44,380
‫And you see now it says false because equals is a method that is inside of the object class.

80
00:05:44,380 --> 00:05:51,040
‫And the object class always has this equals method because every class inherits from object.

81
00:05:51,370 --> 00:05:59,710
‫But now what we're doing is we're implementing our own equals method by using the I equitable interface.

82
00:05:59,710 --> 00:06:07,600
‫So we're using a specific interface that allows us to compare in our own way, so to speak, and implement

83
00:06:07,600 --> 00:06:08,560
‫our own code.

84
00:06:08,560 --> 00:06:13,810
‫So now if we compare the two, we're not comparing if the object is exactly the same that we're comparing

85
00:06:13,810 --> 00:06:21,130
‫it with, but if in our case the time and ours is the same, so the duration in ours is the same, and

86
00:06:21,130 --> 00:06:22,480
‫then it will return true.

87
00:06:22,480 --> 00:06:28,450
‫So if the time and ours is not the same, let's say it's six, then it will return false because the

88
00:06:28,450 --> 00:06:32,740
‫duration is not the same for the two tickets that we're comparing with each other.

89
00:06:32,890 --> 00:06:38,680
‫So this was just an example using a simple interface that exists and as you saw, there are plenty of

90
00:06:38,680 --> 00:06:43,150
‫interfaces that exist automatically when creating a project.

91
00:06:43,150 --> 00:06:48,520
‫But we're going to see how to create our own interfaces and use them in the next video.

92
00:06:48,520 --> 00:06:49,870
‫So see you there.