Encapsulation (computer programming): Difference between revisions

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{{Short description|Bundling of data}}

{{Other uses|Encapsulation (disambiguation){{!}}Encapsulation}}

In [[object-oriented programming]] (OOP), '''encapsulation''' refers to the bundling of data with the methods that operate on that data, or the restricting of direct access to some of an object's components.<ref name="Rogers01" /> Encapsulation is used to hide the values or state of a structured data object inside a [[Class (computer programming)|class]], preventing direct access to them by clients in a way that could expose hidden implementation details or violate state invariance maintained by the methods.

In software systems, '''encapsulation''' refers to the bundling of data with the mechanisms or methods that operate on the data. It may also refer to the limiting of direct access to some of that data, such as an object's components.<ref name="Rogers01" /> Essentially, encapsulation prevents external code from being concerned with the internal workings of an object.

InEncapsulation [[object-orientedallows programming]] (OOP), '''encapsulation''' refersdevelopers to thepresent bundlinga ofconsistent data with the methodsinterface that operateis on that data, or the restrictingindependent of directits accessinternal toimplementation. someAs ofone anexample, object'sencapsulation components.<refcan name="Rogers01" /> Encapsulation isbe used to hide the values or state of a structured data object inside a [[Class (computer programming)|class]],. preventingThis directprevents accessclients tofrom themdirectly byaccessing clientsthis information in a way that could expose hidden implementation details or violate [[State (computer science)|state]] invariance maintained by the methods.

This mechanism is not unique to OOP. Implementations of [[abstract data types]], e.g., [[module (programming)|modules]], offer a similar form of encapsulation. The similarity has been explained by programming language theorists in terms of [[existential types]].<ref>{{harvnb|Pierce|2002|loc=§ 24.2 Data Abstraction with Existentials}}</ref>

Encapsulation also encourages programmers to put all the code that is concerned with a certain set of data in the same class, which organizes it for easy comprehension by other programmers. Encapsulation is a technique that encourages [[Coupling (computer programming)|decoupling]].

All [[object-oriented programming]] (OOP) systems support encapsulation,<ref>{{Cite web |title=What is Object-Oriented Programming (OOP)? |url=https://www.techtarget.com/searchapparchitecture/definition/object-oriented-programming-OOP |access-date=2024-03-02 |website=App Architecture |language=en}}</ref><ref>{{Cite web |title=Encapsulation in Object Oriented Programming (OOPS) |url=https://www.enjoyalgorithms.com/blog/encapsulation-in-oops/ |access-date=2024-03-02 |website=www.enjoyalgorithms.com}}</ref> but encapsulation is not unique to OOP. Implementations of [[abstract data types]], [[module (programming)|modules]], and [[library (computing)|libraries]] also offer encapsulation. The similarity has been explained by programming language theorists in terms of [[existential types]].<ref>{{harvnb|Pierce|2002|loc=§ 24.2 Data Abstraction with Existentials}}</ref>

== Meaning ==

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* A language mechanism for restricting direct access to some of the [[object (computer science)|object]]'s components.<ref>{{cite book |author-link=John C. Mitchell |first=John C. |last=Mitchell |title=Concepts in programming languages |publisher=Cambridge University Press |year=2003 |isbn=978-0-521-78098-8 |page=522}}</ref><ref name=Pierce>{{cite book |last=Pierce |first=Benjamin |author-link=Benjamin C. Pierce |title=Types and Programming Languages |publisher=MIT Press |year=2002 |isbn=978-0-262-16209-8 |page=266 |title-link=Types and Programming Languages }}</ref>

* A language construct that facilitates the bundling of data with the [[method (computer programming)|method]]s <!-- I object to the word method being used here because in lisp languages programmers cannot distinguish methods from normal functions at the [[call site]]. Behavior equivalent to methods may be implemented as normal functions. encapsulation is not dependent on implementation but on behavior--> (or other functions) operating on thatthose data.<ref name=Rogers01>{{cite web |last1=Rogers |first1=Wm. Paul |date=2001-05-18 |df=dmy |url=https://www.infoworld.com/article/2075271/encapsulation-is-not-information-hiding.html |title=Encapsulation is not information hiding |work=[[JavaWorld]] |access-date=2020-07-20}}</ref><ref>{{cite book |first1=Thomas M. |last1=Connolly |first2=Carolyn E. |last2=Begg |title=Database systems: a practical approach to design, implementation, and management |edition= 4th |publisher=Pearson Education |year=2005 |isbn=978-0-321-21025-8 |chapter=Ch. 25: Introduction to Object DMBS § Object-oriented concepts |page=814}}</ref>

Some programming language researchers and academics use the first meaning alone or in combination with the second as a distinguishing feature of [[object-oriented programming]], while some programming languages that provide [[closure (computer programming)|lexical closures]] view encapsulation as a feature of the language [[orthogonality#Computer science|orthogonal]] to object orientation.

The second definition is motivated by the factreflects that in many object-oriented languages, and other related fields, the components are not hidden automatically and this can be overridden;. thusThus, [[information hiding]] is defined as a separate notion by those who prefer the second definition.<!-- this is based on all the refs given above, so no inline cite here-->

The features of encapsulation are supported using [[class (computer programming)|class]]es in most object-oriented languages, although other alternatives also exist.

Encapsulation may also refer to containing a repetitive or complex process in a single unit to be invoked. Object-oriented programming facilitate this at both the method and class levels. This definition is also applicable to [[procedural programming]].<ref>{{Cite book |last=McDonough |first=James E. |title=Object-Oriented Design with ABAP: A Practical Approach |publisher=[[Apress]] |year=2017 |isbn=978-1-4842-2837-1 |___location= |chapter=Encapsulation |doi=10.1007/978-1-4842-2838-8 |via=[[O'Reilly Media|O'Reilly]]}}</ref>

=== Encapsulation and inheritance ===

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== Information hiding ==

{{Main|Information hiding}}

Under the definition that encapsulation "can be used to hide data members and member functions", the internal representation of an [[object (computer science)|object]] is generally hidden from view outside of the object's definition. Typically, only the object's own methods can directly inspect or manipulate its fields. Hiding the internals of the object protects its integrity by preventing users from setting the internal data of the component into an invalid or inconsistent state. A supposed benefit of encapsulation is that it can reduce system complexity, and thus increase [[robustness (computer science)|robustness]], by allowing the developer to limit the interdependencies between software components.{{Citation needed|date=April 2014}}

Some languages like [[Smalltalk]] and [[Ruby (programming language)|Ruby]] only allow access via object methods, but most others (e.g., [[C++]], [[C Sharp (programming language)|C#]], [[Delphi (programming language)|Delphi]] or [[Java (programming language)|Java]]{{sfn|Bloch|2018|loc=Chapter §4 Item 15 Minimize the accessibility of classes and members|pp=73-77}}) offer the programmer a degree ofsome control over what is hidden, typically via keywords like <code>public</code> and <code>private</code>.<ref name=Pierce/> ISO C++ standard refers to <code>protected</code>, <code>private</code> and <code>public</code> as "[[access specifiers]]" and that they do not "hide any information". Information hiding is accomplished by furnishing a compiled version of the source code that is interfaced via a header file.

Almost always, there is a way to override such protection &ndash; usually via [[Reflection (computer programming)|reflection]] API (Ruby, Java, C#, etc.), sometimes by mechanism like [[name mangling]] ([[Python (programming language)|Python]]), or special keyword usage like <code>friend</code> in C++. Systems that provide object-level [[capability-based security]] (adhering to the [[object-capability model]]) are an exception, and guarantee strong encapsulation.

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=== Examples ===

==== Restricting data fields ====

Languages like [[C++]], [[C Sharp (programming language)|C#]], [[Java (programming language)|Java]],{{sfn|Bloch|2018|loc=Chapter §4 Item 15 Minimize the accessibility of classes and members|pp=73-77}} [[PHP]], [[Swift (programming language)|Swift]], and [[Delphi (programming language)|Delphi]] offer ways to restrict access to data fields.

[[File:UML encapsulation.svg]]

Below is an example in [[C Sharp (programming language)|C#]] that shows how access to a data field can be restricted through the use of a <code>private</code> keyword:

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public class Account

{

private decimal accountBalance_accountBalance = 500.00m;

public decimal CheckBalance()

{

return this.accountBalance_accountBalance;

}

}

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myCard.isAvailable(101) // false

</syntaxhighlight>-->

Encapsulation is also possible in non-object-oriented languages. In [[C (programming language)|C]], for example, a structure can be declared in the public API via the header file for a set of functions that operate on an item of data containing data members that are not accessible to clients of the API with the <code>extern</code> keyword.<ref>{{cite book |last1=King |first1=K. N. |url= |title=C Programming: A Modern Approach |date=2008 |publisher=W. W. Norton & Company |isbn=978-0393979503 |page=464 |edition= 2nd |urlpage=https://www.stormingrobots.com/prod/tutorial/pdf/kingBook-ch1to10.pdf |access-date=1 November 2019}}</ref><ref>King, Kim N. ''C programming: a modern approach''. WW Norton & Company, 2008. Ch. 18, p. 464, {{ISBN|0393979504}}</ref>

<syntaxhighlight lang="c">

// Header file "api.h"

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* [[Object-oriented programming]]

* [[Software design pattern]]

* [[Facade pattern]]

== ReferencesCitations ==

{{Reflist}}

== References ==

*{{cite book | title= "Effective Java: Programming Language Guide" |last=Bloch| first=Joshua| publisher=Addison-Wesley | edition=third | isbn=978-0134685991| year=2018}}

[[Category:Object-oriented programming]]

[[Category:Articles with example Java code]]

[[Category:Programming principles]]