All language subtitles for 10. Abstraction in Action

In the last lesson, we've seen how we can create our classes and our objects using Dart.
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But why do we actually need them anyways?
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What purpose do they serve?
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Well in order to understand this, we first have to understand how computers actually work. Behind the
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metal shell and the pretty keyboard and the nice screen,
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a computer is just composed of a large number of switches. And these switches can be in two states, on
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or off. And it's through switching on and off many different switches
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we end up telling the computer what it should do.
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Now if you had to sit there and write all of these ones and zeros in order to program your computer,
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you'd be there for years and in fact this is how people used to code way way back.
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But then we thought that this is a bit painful because in order to just represent the letter A,
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I have to write 01000001. And that is very painful and very time consuming.
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This is what we would say is machine code.
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So we came up with all sorts of ways of making it easier to write programs that sound and look more
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like English so that we can actually interact with the computer without having to get down to the machine
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level and start writing ones and zeros.
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In the early days, a lot of the programming languages were what we would call procedural.
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They would go from top to bottom/ So do this, then this then this then this then this, until forever basically.
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And this is kind of easy to understand. But as your code gets more and more complex, then it gets a bit
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hairy cause it's hard to know when something goes wrong,
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what exactly went wrong?
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Because you have to follow the logic from top to bottom and you have to really untangle it and you can
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really shoot yourself in the foot quite easily.
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So in a lot of places, complexity is always the enemy.
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As humans we have pretty capable brains but we can only hold so much information in it at one time. The
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more complex a program gets, the more likely it is that it will crash and it will have problems and it
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won't perform very well.
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So along came this concept of Object Oriented Programming, and a lot of people really loved the concept.
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So languages that became really big such as Oracles, Java or Apple Swift or in fact Dart,which we're working
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with, are all Object Oriented Programming languages.
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So what does that mean?
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Well it means that we're working with objects to do everything that our app or our program needs to
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do.
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And for those guys who are looking for a job as a software engineer, one of the most common questions
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you get asked is 'What are the four pillars of Object Oriented Programming?'
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What is Object Oriented Programming all about? And the four pillars
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you'll very often hear people reel off are abstraction, encapsulation, inheritance and polymorphism.
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Now it's a mouthful but very few people actually fully understand what these big words actually mean.
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So I want to break it down and show you in the context of our app, why OOP is so great, and how does
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it apply to Dart.
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One of the first pillars is abstraction.
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How can we make something that's complex into smaller pieces to make it more abstract?
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Now if you've taken my courses before, you know how much I love food.
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So in order to understand abstraction, we're going to talk about, you guessed it, food.
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One of my favorite restaurants in Japan are these really tiny kind of hole-in-the-wall places where
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there's only maybe four or five seats. But there's also just one guy who is the waiter, the chef, the cleaning
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staff and he just does everything from behind the bar counter. When you make an order, you do it on a
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vending machine and you give him the order. And then he'll cook you order he'll put it on the table for
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you because it's so easy to reach.
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And then once you're done he'll take your bowl and he'll put it in the dishwasher.
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Now this is really cool but there are some limitations. He can't have more than say 10 customers right?
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Because it will be complete nightmare to try and do all of those jobs himself.
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And that's kind of the downside of that.
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If we have a large piece of code that is trying to do many many things, then it's kind of like just having
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one employee in your restaurant who's cooking, who's waiting on staff, who's taking payment at the cash register,
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who's also taking reservations and bookings. And firstly, good luck finding somebody with the CV that can
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do all of those things.
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And if you hire them, you're going to completely destroy them because one person shouldn't have to do
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so many things.
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And if they did, then you end up having a limitation in how many customers you can serve or how big your
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restaurant can be or how complex your app or program can be.
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So as your program gets more complex and more interesting, then what you want to do is you want a modular
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rise.
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You want to make it more abstract and separate out different jobs. So you'll have the waiter who actually
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brings the food to the customers.
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You'll have the pastry chef who makes the cakes. You'll have the sous-chef and the chef who does the
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rest of the cooking.
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And now, what it means is that everybody has their own jobs.
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They all know what they need to do and they don't get into each other's way and they don't have to all
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do too much at once.
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And now, you can expand your restaurant. You can serve more people and you can do more interesting things
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with more abstraction.
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So if you were creating a program, instead of creating a single large component which is capable of everything
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it's all knowing and all doing, that kind of tends to end up in what we call spaghetti code where everything
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is intermingled with each other.
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And it's a mess to try and debug when something goes wrong or when something doesn't do what you expect
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it to.
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Instead it's much better to split out functionality into different components: the chef component, the
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waiter component, the receptionist and the pastry chef.
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And this is what abstraction is all about, being able to build more complex systems by creating smaller
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pieces that have a defined job or defined role so that you can actually manage the complexity.
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What does that actually mean when we try to apply it to our code?
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Well at the moment, if you look inside our main.dart, you can see that it's getting pretty long right?
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And it's trying to do a lot of things.
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For example it has the questions of our question bank,
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it tries to track which question we're on at the moment, when we need to get a new question we have to
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look into our question bank.
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And it also does things such as putting on the layout for our app, and just you know being able to implement
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the buttons and all of that functionality. And it's getting a bit messy in here.
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If our app got any more complex, then you might start getting a bit confused about exactly what does
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what
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in this main.dart file.
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So let's abstract it. Let's make it more modular. In order to do that,
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we're going to go into our lib folder. We're going to right click and we're going to create a new Dart file.
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And we gonna call this Dart file quiz_brain because this is going to be the brains of our quiz.
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Now when I asked you if you want to add it to Git, go ahead and click
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Yes.
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And now we can create on new quiz_brain.
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And of course it's going to be a class.
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So we're going to create a class called Quiz brain. So remember classes have to start out with capitals.
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And in this class, we're going to define all of the things that a quiz should be and should be able to
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do.
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First of all, our quiz needs to have some questions.
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Let's head into our main.dart,
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and instead of having our question bank mixed in with all of the rest of the functionality, let's go
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ahead and cut it out of here and put it into where it should be inside our quiz_brain.
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The first thing you'll see is we have some errors here.
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It doesn't know what this question thing is.
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Well it's because we haven't actually yet imported our question.dart file which is where that class
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Question is defined now.
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While we're on the topic of our question file, the first thing to note is that at the moment, this class
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is doing a very very simple job.
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It defines the structure of every question namely that it should have a question and it should have
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an answer. When we're creating the constructor for our question class,
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we have named parameters here.
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So in order to create a new question object, we have to write question newQuestion let's call it equals
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a new question.
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And we have to specify that q and also the a.
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Now this is a bit wordy. Given that every question just has a text which is a piece of string and an
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answer which is a boolean,
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it's pretty straightforward to be able to see that if we create a question that has a string.
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This is the text and then it has a boolean,
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this is the answer.
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It's not completely necessary to have the parameter names q and a in there, but this is your judgment
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as well.
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So if you prefer it the other way, keep it the other way.
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But I find that this is much easier to read once we start building up a large bank of questions.
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Speaking of a large bank of questions, it's not much of a quiz app with just three questions
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right?
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So if you open up your readme file, you'll notice that we've already included some pre typed questions.
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There's 13 of them.
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And if you copy everything between the back ticks, all of those questions, you can paste it and replace
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what you have in your question bank at the moment. And they're already formatted so that we create a
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new question object with a question text and an answer. Now all we have to do is to go into our main
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.dart file and fix the errors that we have here. Because we deleted our question bank from our main
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.dart file,
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this no longer exists
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and it tells you as much. But how can we refer to our quiz_brain?
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Well we have to create a new quiz brain object. So first we have to go ahead and import our quiz_brain
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.dart,
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so let's put that in there.
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And now we're able to create a new quiz brain object which is going to be called quizBrain.
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And notice that when we name objects, they start out with a lowercase and we're going to set it to equal
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a new quiz brain object.
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So that constructs a new object which we can now tap into by referring to quizBrain. Down here where
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we have our question bank, instead of using just the question bank which should exist locally,
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we're going to write quizBrain.questionBank, because our question bank is now a property of our
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quiz brain object. And it's right here. It's a list of questions. Now we no longer need to know about questions
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in our main.dart file and we can delete this unused import. Notice that every time you stop requiring
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some code in an import, it'll tell you by making it gray and giving it a squiggly line.
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So let's delete that and we now need to only know about quiz brain inside our main.dart.
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Now we've still got a few more errors down here.
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So my challenge to you is to try and fix everything and run it to make sure that it still works in the
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same way.
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Pause the video and give that a go. All right.
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So down her, we're going to do exactly the same as what we did before. Because our question bank is now
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a property of our quiz brain,
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we have to use the dot notation instead.
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We have the write quizBrain.questionBank. And similarly down here, we have to write quizBrain.
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questionBank, so that we're actually tapping into the actual question
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bank. Now even though we had to add a little bit more code in our main.dart, at least our question
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bank which is now pretty massive, is separated into a separate class. And this now abstracts some of the
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functionality namely the brain for our quiz, into a separate object.
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And now we've abstracted our code just a little bit more. And the other benefit is that say if we were
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to create a different quiz, if we were to create a sports quiz for example, we don't have to change anything
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about our main.dart.
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We just have to provide a new file, say a sport quiz brain and everything in here will still work the
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same.
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And we just have to change the class that we're using to construct the quiz brain.
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So you could have a quiz that has lots of different types of quiz brain, sports and news and general
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knowledge and every time you want to switch between one to the other, you just change the object that
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you're actually using for the current quiz.
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So we've made our code base more reusable more modular and we've separated different jobs into different
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classes.
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Now if we run our app you can see that we now have more questions, 13 to be precise.
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But here's a problem. In our quiz app,
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let's say that we really hate losing.
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Well we can actually change the answer to our questions.
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So for example here we're trying to get the correct answer by tapping into our quiz brain, looking at
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the question bank property and picking out the current question out of the question bank, then tapping
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into the answer.
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And this is what we would call getting. We're getting the value of that correct answer.
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But equally I can also change it.
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I can simply write quiz brain question bank current answer and I can set it to a new value. I can set
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it to whatever it is that I picked, which in this case would be true
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right?
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Well if this happens before I check my answer, then if we hit save and we take a look at the actual correct
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answers and what I get as a result here, you can see that we're on this question about the loudest sound
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produced by an animal and the correct answer should be false.
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But I'm going to press true anyways and it tells me that I got it right.
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So how is it possible? I shouldn't be able to just change that, even if I want to be right all the time.
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This is not very safe for our app.
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Let's comment that out, and in the next lesson we're going to learn how we can make our code a bit better
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and conform with the second pillar of OOP, which is encapsulation.
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So for all of that and more, I'll see you on the next lesson.