1 00:00:01,560 --> 00:00:07,470 Welcome back again we're going to conclude our brief introduction into object oriented programming by 2 00:00:07,470 --> 00:00:13,130 topic but by the blurb verb by talking about polymorphism. 3 00:00:13,250 --> 00:00:14,040 OK. 4 00:00:14,560 --> 00:00:20,790 And man sometimes just the words I want to come out and they don't come out. 5 00:00:21,440 --> 00:00:25,790 But they came out supinely morphism that's a hard word and that's hard enough for it to say as it is 6 00:00:25,830 --> 00:00:31,530 and it's a question that's often asked in interviews for jobs which is funny. 7 00:00:31,650 --> 00:00:36,720 There was like can you please define polymorphism and you're like oh what do I say. 8 00:00:36,720 --> 00:00:41,390 Because the definition is so hard the implementation of it is so easy but the definition is pretty hard. 9 00:00:41,610 --> 00:00:47,440 So we're going to say define polymorphism define Pawley morphism 10 00:00:50,430 --> 00:00:53,790 the condition of occurring in several forms. 11 00:00:54,120 --> 00:00:58,680 The occurrence of different forms among the members of a population or colony or in the lifecycle of 12 00:00:58,680 --> 00:01:00,390 an individual organism. 13 00:01:00,390 --> 00:01:05,460 So it's not this is just generic definitions right talking about having different forms occurring in 14 00:01:05,460 --> 00:01:08,030 several several different forms. 15 00:01:08,040 --> 00:01:08,810 Interesting right. 16 00:01:08,820 --> 00:01:11,890 Occurring in several different forms. 17 00:01:12,300 --> 00:01:15,870 Here's another one some pleased to find it in two sentences. 18 00:01:15,900 --> 00:01:20,740 Polymorphism allows the expression of some sort of contract with potentially many types. 19 00:01:20,760 --> 00:01:26,130 Implementing that contract whether through class inheritance or not in different ways each according 20 00:01:26,130 --> 00:01:31,620 to their own purpose coding code using that contract should not have to care about which implementation 21 00:01:31,680 --> 00:01:35,310 is involved only that the contract that the contract will be obeyed. 22 00:01:35,310 --> 00:01:39,160 I liked that one a lot and this is a programming definition. 23 00:01:39,210 --> 00:01:45,600 So you're going to create a contract and then different things can implement that contract. 24 00:01:45,600 --> 00:01:50,010 But they do it in their own way and you're probably super confused right now and you should be because 25 00:01:50,340 --> 00:01:52,100 that's the textbook definition that's compute. 26 00:01:52,110 --> 00:01:54,250 That's what they teach you in college. 27 00:01:54,270 --> 00:01:59,040 All right let's see if we can confuse our students and not teach them anything practical but teach them 28 00:01:59,040 --> 00:02:01,800 things that don't make any sense. 29 00:02:02,220 --> 00:02:07,980 So let's teach you whether or what they're all about gets started at the playground here and we're going 30 00:02:07,980 --> 00:02:09,360 to call this one. 31 00:02:09,440 --> 00:02:12,340 Paul Lee more fearsome. 32 00:02:13,150 --> 00:02:14,760 OK put it here in swithe. 33 00:02:14,760 --> 00:02:16,790 That's great. 34 00:02:16,800 --> 00:02:20,370 The principle is so simple once you watch me it is going to be like that. 35 00:02:20,820 --> 00:02:25,270 And that's how you should lead in your interview questions by talking about. 36 00:02:25,290 --> 00:02:27,000 Well let me just give you an example of that. 37 00:02:27,030 --> 00:02:32,580 So what we're going to do here is we're going to create a class called Shape. 38 00:02:32,960 --> 00:02:33,720 OK. 39 00:02:33,840 --> 00:02:39,800 And we're going to a property in it called Area OK bar area of type double. 40 00:02:39,990 --> 00:02:44,910 It may or may not have a value and this will put an optional at the end of it and create a function 41 00:02:44,910 --> 00:02:50,390 called calque relate area to. 42 00:02:50,550 --> 00:02:51,340 OK. 43 00:02:51,870 --> 00:02:57,510 Now here's our base class and every shape's going to have a calculate area function. 44 00:02:57,630 --> 00:03:02,580 Ok so here's the advantage of working with a base class. 45 00:03:02,580 --> 00:03:10,470 For instance let's say we didn't do this and I wanted to get rectangles area so I would say class and 46 00:03:10,470 --> 00:03:14,320 then I would have to go and a rectangle. 47 00:03:14,770 --> 00:03:15,450 OK. 48 00:03:15,500 --> 00:03:22,330 And then I'd save our area of type double and then I would say phunk calculate area. 49 00:03:22,810 --> 00:03:23,630 OK. 50 00:03:24,090 --> 00:03:25,850 And an area would be. 51 00:03:26,070 --> 00:03:33,690 And then we need to pass and to lengthen it with here right so laying type double and width of type 52 00:03:33,690 --> 00:03:34,330 double. 53 00:03:34,680 --> 00:03:43,560 And then we would say area equals length times with K and then all of a sudden the boss is like oh no 54 00:03:43,560 --> 00:03:46,240 we need to also create a triangle so we're like OK. 55 00:03:46,540 --> 00:03:58,550 And like triangle or like var area double number like phunk calculate area and then you get a base of 56 00:03:58,560 --> 00:03:59,740 Type of all. 57 00:03:59,890 --> 00:04:03,600 And what does a base times height divided by two. 58 00:04:03,650 --> 00:04:04,340 I think so. 59 00:04:04,490 --> 00:04:12,300 So we get the height which is a double and then so we say you know area equals face times height divided 60 00:04:12,300 --> 00:04:13,520 by two and one. 61 00:04:13,560 --> 00:04:17,070 Put some parentheses peroration. 62 00:04:17,440 --> 00:04:21,640 OK so we've got two classes both doing similar things. 63 00:04:21,650 --> 00:04:22,500 But look at this. 64 00:04:22,610 --> 00:04:27,050 We had to recreate the area property we had to recreate this property here and you know what happens 65 00:04:27,050 --> 00:04:33,700 if in this case one programmer gets lazy and they're like Kelk area and this one is just like you know 66 00:04:33,830 --> 00:04:35,660 let's get area. 67 00:04:35,660 --> 00:04:38,860 So now things are becoming inconsistent and the parameters start changing. 68 00:04:38,870 --> 00:04:40,300 You know base value. 69 00:04:40,550 --> 00:04:42,970 And this is not really good. 70 00:04:43,010 --> 00:04:45,470 We're rewriting code we could break our logic. 71 00:04:45,530 --> 00:04:48,170 This is all trash trash trust trash. 72 00:04:48,170 --> 00:04:49,220 Get rid of it you're fired. 73 00:04:49,230 --> 00:04:50,520 Can't work here anymore. 74 00:04:51,110 --> 00:04:51,640 I'm just kidding. 75 00:04:51,650 --> 00:04:52,850 I'd still hire you. 76 00:04:53,290 --> 00:04:53,600 OK. 77 00:04:53,600 --> 00:04:55,550 So how do we fix this problem. 78 00:04:55,550 --> 00:04:57,080 How do you make things more consistent. 79 00:04:57,080 --> 00:04:58,800 Well we can use polymorphism. 80 00:04:59,210 --> 00:05:04,670 And what we're going to do now instead is we're going to create a new class called triangle of course. 81 00:05:04,670 --> 00:05:11,870 But this time we're going to inherit from Shape OK inherit from shape and all we have to do is obey 82 00:05:11,870 --> 00:05:13,990 the contract which is calculate area. 83 00:05:14,000 --> 00:05:19,310 So what we can do is we can say I want to implement calculate area function and we override it completely 84 00:05:19,970 --> 00:05:21,850 and then all we have to do. 85 00:05:22,130 --> 00:05:23,280 Actually this is wrong. 86 00:05:23,360 --> 00:05:24,860 This needs to have the values in it. 87 00:05:24,860 --> 00:05:31,310 So let's put a value of type double and value be of type double. 88 00:05:31,880 --> 00:05:32,590 OK. 89 00:05:32,720 --> 00:05:41,460 Now we can calculate the area like so and then all we need to do is say area equals ballet time our 90 00:05:41,710 --> 00:05:49,400 time is Balbi like so divided by two this and this and this and this is in itself a try. 91 00:05:51,760 --> 00:05:55,440 And in this case over here we want a rectangle class Rectangle. 92 00:05:56,230 --> 00:06:00,410 And that's going to inherit from shape and we do the same thing here calculate area. 93 00:06:00,520 --> 00:06:07,040 But in this case area equals value a times Velle B. 94 00:06:07,150 --> 00:06:08,630 So that's interesting. 95 00:06:08,690 --> 00:06:11,090 Got two different shapes here. 96 00:06:11,290 --> 00:06:16,950 Implementing the exact same function but the logic inside is different and that is polymorphism OK. 97 00:06:17,230 --> 00:06:27,410 This is one form ok with this one object or form of an object that is taking different forms like so. 98 00:06:27,720 --> 00:06:28,080 OK. 99 00:06:28,090 --> 00:06:33,900 So we were obeying the contract like we saw in that really great stack overflow definition our obeying 100 00:06:33,910 --> 00:06:37,310 the contract and both these cases but they're both doing something different. 101 00:06:37,540 --> 00:06:41,890 And we're still using the same parent class and that's what polymorphism and you use it all the time. 102 00:06:41,890 --> 00:06:47,470 So next when you go in your job interview if you can't read the definition you're like well let me just 103 00:06:47,470 --> 00:06:48,400 give you an example. 104 00:06:48,410 --> 00:06:51,580 Like when he says give me the definition of polymorphous and said Let me give you an example. 105 00:06:51,610 --> 00:07:00,100 Imagine that you have a shape class and you have to calculate the area of shape but you don't know which 106 00:07:00,100 --> 00:07:02,480 shape is going to be passed in at runtime. 107 00:07:02,620 --> 00:07:11,370 So food critic calculate area function and then we also create two more classes like a triangle or rectangle 108 00:07:11,760 --> 00:07:12,650 that inherit from shape. 109 00:07:12,660 --> 00:07:19,130 And then at runtime they can each perform their own area calculation and assign it into the area value. 110 00:07:19,200 --> 00:07:23,370 And so it doesn't have to know beforehand what type of shape you're picking because you have the different 111 00:07:23,370 --> 00:07:24,600 implementation for it. 112 00:07:24,600 --> 00:07:29,370 Or you could say something like that and then be like oh that's a really good example. 113 00:07:29,900 --> 00:07:30,940 You know same thing. 114 00:07:31,140 --> 00:07:36,720 You know if you're building a videogame you know you might have a you might have a humanoid class and 115 00:07:36,720 --> 00:07:42,060 a humanoid class is just you know a base parent class and then the humanoid class might have Orcs because 116 00:07:42,060 --> 00:07:47,220 they're humanoid they got hands and feet they can speak to the Elves but you know elves are magical 117 00:07:47,340 --> 00:07:51,950 and mystical they can do their own things and orcs are brutish and you know ugly. 118 00:07:52,050 --> 00:07:53,930 So they got to put an ugly modifier on there. 119 00:07:53,940 --> 00:07:58,280 And that's actually real that's a real example in games like World of Warcraft and the things they're 120 00:07:58,290 --> 00:08:01,720 using polymorphism and inheritance all over the place. 121 00:08:01,770 --> 00:08:08,520 So that is polymorphism simple principle to understand once you do it and you're going to do it that's 122 00:08:08,520 --> 00:08:08,670 it. 123 00:08:08,670 --> 00:08:12,030 Mark Bryce had slopes dot com polymorphisms.