What are the different types of encapsulation?

Question

This question came from the worst interview questions thread here

So, what are the different types of encapsulation?

Am I right in thinking this basically refers to central OO concepts such as Abstraction, Polymorphism and Inheritance?

My understanding of encapsulation is that it is a method of hiding data / functionality, but I never really considered Polymorphism or Inheritance a form of encapsulation, although I can see how polymorphism could be considered encapsulation as it can hide the exact type of the object you are interacting with.

So, would you say that's about it, or am I missing some core concepts?

edit I just noticed in the comments someone mentioned it could refer to private / public methods, perhaps I'm thinking in to the question too much and expecting a more complicated answer than it really is?

Answer 1

You're thinking too much I think.

http://en.wikipedia.org/wiki/Information_hiding

Excerpt from this article:

Information hiding in computer science is the principle of hiding of design decisions in a computer program that are most likely to change, thus protecting other parts of the program from change if the design decision is changed. The protection involves providing a stable interface which shields the remainder of the program from the implementation (the details that are most likely to change).

One common form of encapsulation is using properties to hide private data fields. An even more common form is the use of OO to encapsulate the complexity of software into well divisoned classes with roles and responsibilities. This is a key tennant of OO, as it moves from a monolithic procedural design style to a more structured style which strives to hide all irrelevant information except that which pertains to the particular task your working on.

Answer 2

Since encapsulation simply refers to "information hiding" then I would imagine that a lot of things can be categorized as encapsulation. However I tend to think of encapsulation as "implementation hiding", in other words it is a tool that I use to create loose coupling between anything I write and anything client of what I have written.

So I tend to believe, pragmatically, that encapsulation is any paradigm or best-practice that allows me to present a clean, solid interface to any client.

Answer 3

It is my view and understanding that the term encapsulation (to encapsulate) is the art/science of capturing the essence of something for the purpose of display. In fact, by definition - to encapsulate is to package something or enclose it in another container. Therefore the term encapsulation would mean to take the essence of what you are attempting to achieve and packaging it in a useful form so that it can be reused as necessary.

So to interpret this, it would mean to package material in a form that would make it more useful later.

So really...interpret this as you see fit. I see it as taking a bunch of algorithms and utilities and creating a class structure that can be used as an API in other projects. This encapsulated code could be inherited and/or extended to make it useful for modified purposes without changing the underlying essence of the API.

Therefore, abstraction, polymorphism and inheritance aren't forms of encapsulation, but forms of extending and modifying encapsulated code.

Different forms of encapsulation would mean the modifiers on properties, methods, fields and classes - that is public, private, static, virtual (in C#). Everything else (i.e. overloads, overrides, shadows) is a modification or an extension to that encapsulation.

You may consider the modified code an encapsulation which could then be further inherited/abstracted/extended, but the package which is to be extended is the encapsulated product.

Answer 4

Encapsulation is more than simply information hiding. That is one aspect of it. It has to do with the interface to a module. An Interface provides two very important functions: encapsulation and abstraction.

Abstraction is when a client of module does not need to know more than is ion the interface.

and

Encapsulation is when a client of a module isn't able to know more than is in the interface.

(Both definitions from Using UML by Perdita Stevens)

Answer 5

Generally the usage of the word is pretty close to what it says. You encapsulate something when you contain it, and don't let any of the deals loose. The best way to think about it is that you are taking something and putting it into a black-box where no one can see the details anymore. The box hides everything, providing some other disassociated interface in its place.

Information hiding is just one aspect of encapsulation, since along with the data you can also hide any of the details of the code itself. The purpose of encapsulating a part of your system is to draw that bit of complexity away from the whole, thus making it easier to understand the separate details (on both sides). More?

Paul.

Answer 6

Encapsulation is defined by the International Organisation for Standardization's International Standard: "Information technology – Open Distributed Processing," ISO/IEC 10746, 1998.

It's defined in terms of more primitive definitions:

Entity: Any concrete or abstract thing of interest.

Object: A model of an entity. An object is characterised by its behaviour and, dually, by its state.

Behaviour (of an object): A collection of actions with a set of constraints on when they may occur.

Interface: An abstraction of the behaviour of an object that consists of a subset of the interactions of that object together with a set of constraints on when they may occur.

Encapsulation: the property that the information contained in an object is accessible only through interactions at the interfaces supported by the object.

The ISO does not define different types of encapsulation.

Other posts have mentioned information hiding. The ISO does not define encapsulation explicitly in terms of information hiding, though it does seem implicit, see "Encapsulation theory fundamentals," at http://www.edmundkirwan.com/pub/

Ed.