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Recently I was talking to a very experienced programmer (8+ years of experience) and he told me that "combining data with functions that work with them in a capsula" is a wrong term for encapsulation. He told me that that was what encapsulation allowed me to do, but not what encapsulation itself was. He told me that as soon as inheritance is not possible without encapsulation, encapsulation must be just a capsula creation (class or anything like that). But today I got interviewed by a less experienced programmer and he was so sure all those classic definitions on wikipedia were right he told me not to even think of passing the interview. So I tried to google all that stuff about encapsulation, and about inheritence not being possible without encapsulation, but didn't find anything. But I can't believe that experienced programmer was wrong, he convienced not only me, but other experienced programmers too. Maybe that correct definition is just something that is lost in the chunks of useless and unimportant info?

So please, give me answers on these two questions:

1) can inheritence be possible without encapsulation? (A class's Inheritence from a class)

2) If not, then can we consider declaring a class encapsulation? Because only after declaring a class we can inherit.

Марк Павлович
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  • Well, the English Wikipedia article mentions two related definitions. Encapsulation in terms of hiding internal variables to the outside world is perfectly possible without inheritance. You might also want to read [this](https://stackoverflow.com/questions/742341/difference-between-abstraction-and-encapsulation). – MC Emperor Mar 25 '19 at 07:25
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    I know encapsulation is possible without inheritence. I ask if inheritence is possible without encapsulation – Марк Павлович Mar 25 '19 at 07:26
  • If inheritance in OOP context is the possibility to add methods to an existing class by extending this class, then no encapsulation is involved at all. So yes, it's possible. – MC Emperor Mar 25 '19 at 07:34
  • Of course it is, but it will end up in unmaintainable code very quickly. – Svetlin Zarev Mar 25 '19 at 07:37
  • But encapsulation is not creating a class? – Марк Павлович Mar 25 '19 at 07:52
  • Encapsulation can be done in languages that aren't OO too, for example a function encapsulates functionality. Or consider `struct`s. – P Varga Mar 25 '19 at 10:07

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Well, I'm Sorry, but I fail to see the connection between encapsulation and inheritance.

Encapsulation is hiding your internal implementation behind a publicly visible API.
Basically, it's a separation between a type's actual implementation and what it exposes.
In a broad sense, one can look at even the human body and see encapsulation:
For example: You are breathing air in and out, that's your public API, but the internals of what your body is doing with this air are hidden away inside your respiratory system - your lunges passes oxygen to your blood and collects from it carbon dioxide in return - thus changing the mixture ratio of the gasses in the air you breath, but none of this is visible to the outside world.

Inheritance, in the OOP world, is the ability to take a specific object, and derive an even more specific object from it, while adding capabilities (and sometimes mutating existing capabilities via overriding).
For example: A Dog is a kind of Mammal which is a kind of Animal.
An Animal might contain methods such as Eat() and properties such as Weight and Age.
A Mammal might override the Eat() method to implement suckling (from it's mother's breast) as an infant, but depending on it's age eating solid foods.
A Dog might introduce another capability such as Bark.
All of this have nothing to do with encapsulation as desribed in the previous paragraph.

Inheritance is tightly related to another core principle of object oriented programming called Polymorphism - basically, the ability to reference a derived class using it's base class type - perhaps you (or the interviewer) are confusing the two?

However, today is the first time I've seen another definition of encapsulation (and I've been working with oop languages for about two decades now):

A language construct that facilitates the bundling of data with the methods (or other functions) operating on that data.

Under that definition, encapsulation is the process of creating capsules - stand-alone code snippets that holds data and ways to interact with it - a.k.a types, classes, etc', and is somewhat related to inheritance - in order to inherit a type, that type first needs to be defined.
However, the way I see it, this definition is not enough to define encapsulation. It can be a part of the definition, but not a stand-alone definition of encapsulation.

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Zohar Peled
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