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Today, we start super important topic, many even of engineers couldn't apply in practice all aspects

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of this knowledge because to understand this topic from all sides, you need to practice a lot as you

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get more experience or information, which I'm going to share with you will start to make sense.

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I spent a lot of time to select the right person to make complex things easier.

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And today I will try to explain you object oriented programming.

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So today, let's start from OPIS basics.

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In this lesson we'll learn theory and I will explain in simple words what object oriented programming

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is, where we are going to discuss what object oriented programming means.

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And it is always better to understand first why we need or be and how it can help us in creating software.

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We'll briefly discuss functional programming approach so you would be able to understand the difference

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and better understand OPIS approach and take into account that this is a lesson about all basics.

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We'll talk about key object oriented programming principles.

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So let's start let's come up with a definition of OPIS first.

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There are multiple definitions of what is or B, I'm going to share with you different ones.

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And my own Wikipedia tells us that OPIS is programming paradigm based on the concept of object as a

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definition of OPIS is the next one or is a computer programming model that organizes software design

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around the objects rather than functions.

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This definition clearly describes the difference between all AP and functional programming.

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We'll talk about functional programming a little bit later.

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My own definition sounds like this object oriented programming is a software design approach in which

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concept of object occupies the first place.

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In each definition we see that the concept of object is mentioned.

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OK, then let's find the answer on the next question.

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What is the object and object oriented programming?

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Everything is an object.

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Array is our object.

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Connection to database is the object and expect the situation during the program.

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Execution is the object, but this definition is very vast.

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We need more specifics and let me simplify the definition of the object.

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Imagine a car, a car, doors, headlights, body wheels, trunk engine and sided steering wheel color

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and lots more.

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What we have just described is called data structure.

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We describe something abstract with key properties which allow us to distinguish car from plane.

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Right now we have nothing more than a list of properties, which brings us to specific data organization

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that enables efficient access and modification.

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We can change wheels if we want, or we can change color of the car.

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But this will be still a pure data structure in our program.

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What does this car need to become an object?

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This car needs to have behavior which will allow to manipulate with its own data the properties we have

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listed.

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We call this behavior methods.

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Imagine that car has such behavior, astroland the headlight or start engine or turn right or turn left

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and so on.

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In case our car has such behavior, we can call it the object.

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Now let me share with you my own definition of object.

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Object, first of all, is a visual entity with a specific list of properties which can distinguish

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it from other objects and behavior which allow to manipulate with these properties.

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In other words, data plus behavior equals to object.

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Does it make sense?

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Object is always an instance of some specific class.

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Things become more interesting.

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Now we need to understand what acrostics.

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I will try to explain what class is in a few words, because we are going to have separate lesson dedicated

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to classes.

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But I need to understand the concept of the class now to understand what object is.

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Treat the class as the template for an object.

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Imagine you a car manufacturer and you need to create millions of cars.

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You know that each car will have color wheels, body, headlights, engine and lots more.

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We also know that car should be able to drive, start and stop engine, accelerate, brake and so on.

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We have just described the class for a car with properties and behavior, but each car might have different

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color, different, but a petrol engine or diesel engine or electric one.

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Besides that, each car can drive radically differently, I believe.

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Now you understand that object.

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Always an instance of some class.

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If you understand this, we already probably are interested.

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What are the approaches for software development exist?

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One of the most popular programming paradigms is functional programming.

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If an object oriented programming, our main concept is object in functional programming, our main

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concept is function.

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In other words, functional programming is not bothering about grouping data together with related behavior

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and about describing of control flow.

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We have specific task and we have specific functions that can deal with this task.

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Functional programming expresses the logic of a computation which approach is better.

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This is wrong question.

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Because it is not complete enough.

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The right question is which approach is better for some specific task because functional programming

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approach works the best way.

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You don't care about order of functions, execution for simple data manipulations, functional programming,

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solution in some degrees, easier and faster to implement.

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Sometimes it is even easier to support, but for complex enterprise solutions, functional programming

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approach can turn your project maintenance in the nightmare.

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Object oriented approach allows you to organize your code and programming execution in structured way.

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During the course, we'll discuss with you different Glynco techniques, which relies on basic principles.

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So now I believe you understand the difference between ALBE and functional programming.

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Let's name exact reasons why and when we need to follow OPIS design.

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Nowadays, you can't implement mobile application of web application if you don't understand or B approach

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or in most cases the most natural and pragmatic approach.

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I'm not trying to say is that OP is the one true way.

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I just want to highlight the list of advantages which in most cases helps to solve even complex software

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development tasks, modularity.

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And in case something goes wrong in your program, you know where to look at their problems with calculation

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of personal discount for user would need to take a look at user object.

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If you would follow key or P principles, your code will be structured or allows you to have low coupling

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in your code and high cohesion, which makes maintenance of your code much easier.

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Scalability because of modularity.

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And if you follow opis design principles, you can scale your software easily and in a predictable manner.

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If you don't follow opihi approach, adding a new piece of functionality in your program may cause significant

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changes in all existing code, which in turn increased risk of new defects associated with those changes.

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Lower cost of development or BYDESIGN allows you to reuse code.

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When you reuse code, you decrease the number of places where potential defects can appear.

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Also, spend less time to reuse already existing method than to write new methods from scratch.

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Security and reliability.

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Basic principles allow you to hide details of implementation from user of your objects.

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Or ByDesign allows you to build a robust design with independent modules that in turn makes the software

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more secure and reliable.

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Definitely, when you become senior developer, you would find disadvantages in orbit.

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But when a candidate starts arguing with me during the interview and hating OPIS approach, usually

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I ask him what is better for some imaginary business case?

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And these people always lose this fight because they need to understand that programming is always just

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a question of tradeoffs between maintainability, scalability, speed of development, good quality

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and reliability.

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And now when you understand on a high level what is object oriented programming and why we need to learn

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it, let's review.

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Basic core principles are inheritance, encapsulation, polymorphism, abstraction.

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Let's go one by one inheritance to understand inheritance, let's consider the next example the remember

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we discussed a class of the car in this lesson and now imagine that you need to create not Sadun but

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sports car or family car was Xerces.

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Would you describe class for sport car from scratch.

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You don't need to do this because sports car also going to have four wheels, also going to have engine,

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but something will be different.

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Most likely you are going to have only two seats in the car and additional attributes of the sports

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car like smaller probably clutch pedal for sport, manual transmission and something else.

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I believe you got my point.

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Inheritance allows you to create a new class based on another one.

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New class can extend existing one and share properties and behavior.

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New class is called child class and by the class is called parent class.

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Inheritance allows you to reuse code and to create new classes without reinventing the wheel encapsulation.

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The key principle tells us to keep data and code that can manipulate this data together.

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It is also about keeping data and the code safe from external interference.

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To understand it better, let me demonstrate encapsulation.

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In real life, you have a car.

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Car is a separate object and there is a gas pedal in it.

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Gas pedal is external interface, which said the way how will interact with our car.

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When we push down gas pedal, a lot of things happen.

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The throttle is open to let some air in.

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Meanwhile, food is fed to intake.

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Manifold sensors regulate when throttle should be closed and so on and everything is done to accelerate

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your car.

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Do you see how many details are encapsulated from you inside the car?

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But you don't care.

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You don't want to control all these actions.

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You just want to push gas pedal to accelerate your car and you don't have access.

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Control how much food to feed in different cases, you'll get your car handle such kind of questions,

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do you understand better now?

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What is encapsulation in programming and modifiers exist to facilitate the encapsulation of components.

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For example, in Java you have next access modifiers privat the strictest one.

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You have access to fields and methods only within the specific class.

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You can't access private elements outside of this class default access level.

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Within the same package, elements with default access modifier can be accessed outside of the package

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protected access level within the package and outside of the package.

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In the channel classes access outside of the package and outside of a child class is not possible.

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Public access level from everywhere.

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You can access elements with public money, fire from within the class, outside of the class, within

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the package and outside of the package to keep focus on the basic principles.

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In this lesson, we'll discuss on the theory in the next.

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Lessons will make a deep dive into practice part, including access modifiers.

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I believe now it is clear what this encapsulation principle means.

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The next principle is polymorphism.

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Let me explain polymorphism in simple words and again of Óscar example.

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Imagine you have two different cars.

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One was electric engine, another was petrol engine.

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Both are going to have Botten start engine.

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In most cases, behaviour will be similar, engine will be started and you will be able to drive.

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But the way how engine will be started is completely different.

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In Kavis, petrol engine car system will feed fuel to the engine to start it in Kavis Electric Engine,

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a huge blast of power will drive car like it's shown on the slide.

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You have steering the wheel and each car has.

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But the way how a steering system work is different in each car.

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In this example you can have a single interface, but multiple implementations do feel what polymorphism

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is all about.

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The same word can mean different things in different contexts.

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What we have just discussed called method overriding you your right behaviour in the separate lesson.

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I am going to show you how polymorphism works in Java.

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For now, I need you to understand the concept of OPIS and basic principles.

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And the last but not least principle is abstraction and some literature.

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This principle even not mentioned as a basic or principle, but I believe we can consider as this principle

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as important as other ones we discussed.

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Let me explain of what abstraction is.

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If I would ask you, what is the difference between the car and the plane?

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What will you say?

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You would try to list some key features of a car and the plane.

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You're trying to come up with abstraction, which should be enough to differentiate car and plane,

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create abstraction, which works the best for your business needs.

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It is not easiest thing to do, but if you create good abstraction for a specific case, it would allow

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you to not duplicate code to support good scalability of your units and lots more.

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This principle is a very important one and it requires time to use it in the right manner.

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Let's take a look now.

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What we have learned today, the we learned what is or be and what is the difference between object

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oriented and functional programming.

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We discuss advantages of OPIS and why we need to learn it.

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And what is also very important.

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We learned basic principles.

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That's all what I wanted to share with you in this lesson.

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This is our start of learning of object oriented programming.

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I would be glad to recommend your literature to read as your homework, but I wouldn't recommend you

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read anything.

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So far my opinion, the topic of object oriented programming in majority books described chaotically

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by saying this, I mean in books, a lot of terms, cost structures, new keywords, which we are going

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to learn are mixed in the same chapters.

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I spent a lot of time thinking on the structure of lessons and how to explain to my students and my

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experience of teaching proofs that the sequence of lessons which I suggest brings a clear vision of

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OPIS in the shortest possible time.

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So now make sure you understand the content of this lesson before we move further.