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Encapsulation (computer programming)

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</style><div role="note" class="hatnote navigation-not-searchable">For other uses, see <a href="Encapsulation_(disambiguation)" class="mw-redirect mw-disambig" title="Encapsulation (disambiguation)">Encapsulation</a>.</div>

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.<a href="#cite_note-Rogers01-1">[1]</a> Essentially, encapsulation prevents external code from being concerned with the internal workings of an object.

Encapsulation allows developers to present a consistent interface that is independent of its internal implementation. As one example, encapsulation can be used to hide the values or state of a structured data object inside a <a href="Class_(computer_programming)" title="Class (computer programming)">class</a>. This prevents clients from directly accessing this information in a way that could expose hidden implementation details or violate <a href="State_(computer_science)" title="State (computer science)">state</a> invariance maintained by the methods.

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 <a href="Coupling_(computer_programming)" title="Coupling (computer programming)">decoupling</a>.

All <a href="Object-oriented_programming" title="Object-oriented programming">object-oriented programming</a> (OOP) systems support encapsulation,<a href="#cite_note-2">[2]</a><a href="#cite_note-3">[3]</a> but encapsulation is not unique to OOP. Implementations of <a href="Abstract_data_types" class="mw-redirect" title="Abstract data types">abstract data types</a>, <a href="Module_(programming)" class="mw-redirect" title="Module (programming)">modules</a>, and <a href="Library_(computing)" title="Library (computing)">libraries</a> also offer encapsulation. The similarity has been explained by programming language theorists in terms of <a href="Existential_types" class="mw-redirect" title="Existential types">existential types</a>.<a href="#cite_note-4">[4]</a>

<div class="mw-heading mw-heading2"><h2 id="Meaning">Meaning</h2></div>

In <a href="Object-oriented_programming_languages" class="mw-redirect" title="Object-oriented programming languages">object-oriented programming languages</a>, and other related fields, encapsulation refers to one of two related but distinct notions, and sometimes to the combination thereof:<a href="#cite_note-5">[5]</a><a href="#cite_note-Dale-6">[6]</a>

<ul><li>A language mechanism for restricting direct access to some of the <a href="Object_(computer_science)" title="Object (computer science)">object</a>'s components.<a href="#cite_note-7">[7]</a><a href="#cite_note-Pierce-8">[8]</a></li>

<li>A language construct that facilitates the bundling of data with the <a href="Method_(computer_programming)" title="Method (computer programming)">methods</a> (or other functions) operating on those data.<a href="#cite_note-Rogers01-1">[1]</a><a href="#cite_note-9">[9]</a></li></ul>

Some programming language researchers and academics use the first meaning alone or in combination with the second as a distinguishing feature of <a href="Object-oriented_programming" title="Object-oriented programming">object-oriented programming</a>, while some programming languages that provide <a href="Closure_(computer_programming)" title="Closure (computer programming)">lexical closures</a> view encapsulation as a feature of the language <a href="Orthogonality#Computer_science" title="Orthogonality">orthogonal</a> to object orientation.

The second definition reflects that in many object-oriented languages, and other related fields, the components are not hidden automatically and this can be overridden. Thus, <a href="Information_hiding" title="Information hiding">information hiding</a> is defined as a separate notion by those who prefer the second definition.

The features of encapsulation are supported using <a href="Class_(computer_programming)" title="Class (computer programming)">classes</a> 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 <a href="Procedural_programming" title="Procedural programming">procedural programming</a>.<a href="#cite_note-10">[10]</a>

<div class="mw-heading mw-heading3"><h3 id="Encapsulation_and_inheritance">Encapsulation and inheritance</h3></div>

The authors of <a href="Design_Patterns" title="Design Patterns">Design Patterns</a> discuss the tension between <a href="Inheritance_(object-oriented_programming)" title="Inheritance (object-oriented programming)">inheritance</a> and encapsulation at length and state that in their experience, designers overuse inheritance. They claim that inheritance often breaks encapsulation, given that inheritance exposes a subclass to the details of its parent's implementation.<a href="#cite_note-GoF-11">[11]</a> As described by the <a href="Yo-yo_problem" title="Yo-yo problem">yo-yo problem</a>, overuse of inheritance and therefore encapsulation, can become too complicated and hard to debug.

<div class="mw-heading mw-heading2"><h2 id="Information_hiding">Information hiding</h2></div>

<div role="note" class="hatnote navigation-not-searchable">Main article: <a href="Information_hiding" title="Information hiding">Information hiding</a></div>

Under the definition that encapsulation "can be used to hide data members and member functions", the internal representation of an <a href="Object_(computer_science)" title="Object (computer science)">object</a> is generally hidden 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 <a href="Robustness_(computer_science)" title="Robustness (computer science)">robustness</a>, by allowing the developer to limit the interdependencies between software components.

Some languages like <a href="Smalltalk" title="Smalltalk">Smalltalk</a> and <a href="Ruby_(programming_language)" title="Ruby (programming language)">Ruby</a> only allow access via object methods, but most others (e.g., <a href="C%2B%2B" title="C++">C++</a>, <a href="C_Sharp_(programming_language)" title="C Sharp (programming language)">C#</a>, <a href="Delphi_(programming_language)" class="mw-redirect" title="Delphi (programming language)">Delphi</a> or <a href="Java_(programming_language)" title="Java (programming language)">Java</a><a href="#cite_note-FOOTNOTEBloch201873–77Chapter_§4_Item_15_Minimize_the_accessibility_of_classes_and_members-12">[12]</a>) offer the programmer some control over what is hidden, typically via keywords like <code>public</code> and <code>private</code>.<a href="#cite_note-Pierce-8">[8]</a> ISO C++ standard refers to <code>protected</code>, <code>private</code> and <code>public</code> as "<a href="Access_specifiers" class="mw-redirect" title="Access specifiers">access specifiers</a>" 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 – usually via <a href="Reflection_(computer_programming)" class="mw-redirect" title="Reflection (computer programming)">reflection</a> API (Ruby, Java, C#, etc.), sometimes by mechanism like <a href="Name_mangling" title="Name mangling">name mangling</a> (<a href="Python_(programming_language)" title="Python (programming language)">Python</a>), or special keyword usage like <code>friend</code> in C++. Systems that provide object-level <a href="Capability-based_security" title="Capability-based security">capability-based security</a> (adhering to the <a href="Object-capability_model" title="Object-capability model">object-capability model</a>) are an exception, and guarantee strong encapsulation.

<div class="mw-heading mw-heading3"><h3 id="Examples">Examples</h3></div>

<div class="mw-heading mw-heading4"><h4 id="Restricting_data_fields">Restricting data fields</h4></div>

Languages like <a href="C%2B%2B" title="C++">C++</a>, <a href="C_Sharp_(programming_language)" title="C Sharp (programming language)">C#</a>, <a href="Java_(programming_language)" title="Java (programming language)">Java</a>,<a href="#cite_note-FOOTNOTEBloch201873–77Chapter_§4_Item_15_Minimize_the_accessibility_of_classes_and_members-12">[12]</a> <a href="PHP" title="PHP">PHP</a>, <a href="Swift_(programming_language)" title="Swift (programming language)">Swift</a>, and <a href="Delphi_(programming_language)" class="mw-redirect" title="Delphi (programming language)">Delphi</a> offer ways to restrict access to data fields.

Below is an example in <a href="C_Sharp_(programming_language)" title="C Sharp (programming language)">C#</a> that shows how access to a data field can be restricted through the use of a <code>private</code> keyword:

<div class="mw-highlight mw-highlight-lang-csharp mw-content-ltr" dir="ltr"><pre>class Program

{

public class Account

{

private decimal _accountBalance = 500.00m;

public decimal CheckBalance()

{

return _accountBalance;

}

static void Main()

{

Account myAccount = new Account();

decimal myBalance = myAccount.CheckBalance();

/* This Main method can check the balance via the public

* "CheckBalance" method provided by the "Account" class

* but it cannot manipulate the value of "accountBalance" */

}

}

</pre></div>

Below is an example in <a href="Java_(programming_language)" title="Java (programming language)">Java</a>:

<div class="mw-highlight mw-highlight-lang-java mw-content-ltr" dir="ltr"><pre>public class Employee {

private BigDecimal salary = new BigDecimal(50000.00);

public BigDecimal getSalary() {

return this.salary;

}

public static void main() {

Employee e = new Employee();

BigDecimal sal = e.getSalary();

}

}

</pre></div>

Encapsulation is also possible in non-object-oriented languages. In <a href="C_(programming_language)" title="C (programming language)">C</a>, 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.<a href="#cite_note-13">[13]</a>

<div class="mw-highlight mw-highlight-lang-c mw-content-ltr" dir="ltr"><pre>// Header file "api.h"

struct Entity; // Opaque structure with hidden members

// API functions that operate on 'Entity' objects

extern struct Entity * open_entity(int id);

extern int process_entity(struct Entity *info);

extern void close_entity(struct Entity *info);

// extern keywords here are redundant, but don't hurt.

// extern defines functions that can be called outside the current file, the default behavior even without the keyword

</pre></div>

Clients call the API functions to allocate, operate on, and deallocate objects of an <a href="Opaque_data_type" title="Opaque data type">opaque data type</a>. The contents of this type are known and accessible only to the implementation of the API functions; clients cannot directly access its contents. The source code for these functions defines the actual contents of the structure:

<div class="mw-highlight mw-highlight-lang-c mw-content-ltr" dir="ltr"><pre>// Implementation file "api.c"

#include "api.h"

struct Entity {

int ent_id; // ID number

char ent_name[20]; // Name

... and other members ...

};

// API function implementations

struct Entity * open_entity(int id)

{ ... }

int process_entity(struct Entity *info)

{ ... }

void close_entity(struct Entity *info)

{ ... }

</pre></div>

<div class="mw-heading mw-heading4"><h4 id="Name_mangling">Name mangling</h4></div>

<div role="note" class="hatnote navigation-not-searchable">Main article: <a href="Name_mangling" title="Name mangling">Name mangling</a></div>

Below is an example of <a href="Python_(programming_language)" title="Python (programming language)">Python</a>, which does not support variable access restrictions. However, the convention is that a variable whose name is prefixed by an underscore should be considered private.<a href="#cite_note-14">[14]</a>

<div class="mw-highlight mw-highlight-lang-python mw-content-ltr" dir="ltr"><pre>class Car:

def __init__(self) -> None:

self._maxspeed = 200

def drive(self) -> None:

print(f"Maximum speed is {self._maxspeed}.")

redcar = Car()

redcar.drive() # This will print 'Maximum speed is 200.'

redcar._maxspeed = 10

redcar.drive() # This will print 'Maximum speed is 10.'

</pre></div>

<ul><li><a href="Inheritance_(object-oriented_programming)" title="Inheritance (object-oriented programming)">Inheritance (object-oriented programming)</a></li>

<li><a href="Object-oriented_programming" title="Object-oriented programming">Object-oriented programming</a></li>

<li><a href="Software_design_pattern" title="Software design pattern">Software design pattern</a></li>

<li><a href="Facade_pattern" title="Facade pattern">Facade pattern</a></li></ul>

<div class="mw-heading mw-heading2"><h2 id="Citations">Citations</h2></div>

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</style><cite id="CITEREFRogers2001" class="citation web cs1">Rogers, Wm. Paul (18 May 2001). <a rel="nofollow" class="external text" href="https://www.infoworld.com/article/2075271/encapsulation-is-not-information-hiding.html">"Encapsulation is not information hiding"</a>. <a href="JavaWorld" class="mw-redirect" title="JavaWorld">JavaWorld</a>. Retrieved 2020-07-20.</cite>

</li>

<li id="cite_note-2"><a href="#cite_ref-2">^</a> <cite class="citation web cs1"><a rel="nofollow" class="external text" href="https://www.techtarget.com/searchapparchitecture/definition/object-oriented-programming-OOP">"What is Object-Oriented Programming (OOP)?"</a>. App Architecture. Retrieved 2024-03-02.</cite>

</li>

<li id="cite_note-3"><a href="#cite_ref-3">^</a> <cite class="citation web cs1"><a rel="nofollow" class="external text" href="https://www.enjoyalgorithms.com/blog/encapsulation-in-oops/">"Encapsulation in Object Oriented Programming (OOPS)"</a>. www.enjoyalgorithms.com. Retrieved 2024-03-02.</cite>

</li>

<li id="cite_note-4"><a href="#cite_ref-4">^</a> <a href="#CITEREFPierce2002">Pierce 2002</a>, § 24.2 Data Abstraction with Existentials

</li>

<li id="cite_note-5"><a href="#cite_ref-5">^</a> <cite id="CITEREFScott2006" class="citation book cs1">Scott, Michael Lee (2006). Programming language pragmatics (2 ed.). Morgan Kaufmann. p. 481. <a href="ISBN_(identifier)" class="mw-redirect" title="ISBN (identifier)">ISBN</a> <bdi>978-0-12-633951-2</bdi>. <q>Encapsulation mechanisms enable the programmer to group data and the subroutines that operate on them together in one place, and to hide irrelevant details from the users of an abstraction</q></cite>

</li>

<li id="cite_note-Dale-6"><a href="#cite_ref-Dale_6-0">^</a> <cite id="CITEREFDaleWeems2007" class="citation book cs1">Dale, Nell B.; Weems, Chip (2007). Programming and problem solving with Java (2nd ed.). Jones & Bartlett. p. 396. <a href="ISBN_(identifier)" class="mw-redirect" title="ISBN (identifier)">ISBN</a> <bdi>978-0-7637-3402-2</bdi>.</cite>

</li>

<li id="cite_note-7"><a href="#cite_ref-7">^</a> <cite id="CITEREFMitchell2003" class="citation book cs1"><a href="John_C._Mitchell" title="John C. Mitchell">Mitchell, John C.</a> (2003). Concepts in programming languages. Cambridge University Press. p. 522. <a href="ISBN_(identifier)" class="mw-redirect" title="ISBN (identifier)">ISBN</a> <bdi>978-0-521-78098-8</bdi>.</cite>

</li>

<li id="cite_note-Pierce-8">^ <a href="#cite_ref-Pierce_8-0">a</a> <a href="#cite_ref-Pierce_8-1">b</a> <cite id="CITEREFPierce2002" class="citation book cs1"><a href="Benjamin_C._Pierce" title="Benjamin C. Pierce">Pierce, Benjamin</a> (2002). <a href="Types_and_Programming_Languages" title="Types and Programming Languages">Types and Programming Languages</a>. MIT Press. p. 266. <a href="ISBN_(identifier)" class="mw-redirect" title="ISBN (identifier)">ISBN</a> <bdi>978-0-262-16209-8</bdi>.</cite>

</li>

<li id="cite_note-9"><a href="#cite_ref-9">^</a> <cite id="CITEREFConnollyBegg2005" class="citation book cs1">Connolly, Thomas M.; Begg, Carolyn E. (2005). "Ch. 25: Introduction to Object DMBS § Object-oriented concepts". Database systems: a practical approach to design, implementation, and management (4th ed.). Pearson Education. p. 814. <a href="ISBN_(identifier)" class="mw-redirect" title="ISBN (identifier)">ISBN</a> <bdi>978-0-321-21025-8</bdi>.</cite>

</li>

<li id="cite_note-10"><a href="#cite_ref-10">^</a> <cite id="CITEREFMcDonough2017" class="citation book cs1">McDonough, James E. (2017). "Encapsulation". Object-Oriented Design with ABAP: A Practical Approach. <a href="Apress" class="mw-redirect" title="Apress">Apress</a>. <a href="Doi_(identifier)" class="mw-redirect" title="Doi (identifier)">doi</a>:<a rel="nofollow" class="external text" href="https://doi.org/10.1007%2F978-1-4842-2838-8">10.1007/978-1-4842-2838-8</a>. <a href="ISBN_(identifier)" class="mw-redirect" title="ISBN (identifier)">ISBN</a> <bdi>978-1-4842-2837-1</bdi> – via <a href="O'Reilly_Media" title="O'Reilly Media">O'Reilly</a>.</cite>

</li>

<li id="cite_note-GoF-11"><a href="#cite_ref-GoF_11-0">^</a> <cite id="CITEREFGammaHelmJohnsonVlissides1994" class="citation book cs1">Gamma, Erich; Helm, Richard; Johnson, Ralph; Vlissides, John (1994). <a rel="nofollow" class="external text" href="https://archive.org/details/designpatternsel00gamm">Design Patterns</a>. Addison-Wesley. <a href="ISBN_(identifier)" class="mw-redirect" title="ISBN (identifier)">ISBN</a> <bdi>978-0-201-63361-0</bdi>.</cite>

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<li id="cite_note-FOOTNOTEBloch201873–77Chapter_§4_Item_15_Minimize_the_accessibility_of_classes_and_members-12">^ <a href="#cite_ref-FOOTNOTEBloch201873–77Chapter_§4_Item_15_Minimize_the_accessibility_of_classes_and_members_12-0">a</a> <a href="#cite_ref-FOOTNOTEBloch201873–77Chapter_§4_Item_15_Minimize_the_accessibility_of_classes_and_members_12-1">b</a> <a href="#CITEREFBloch2018">Bloch 2018</a>, pp. 73–77, Chapter §4 Item 15 Minimize the accessibility of classes and members.

</li>

<li id="cite_note-13"><a href="#cite_ref-13">^</a> <cite id="CITEREFKing2008" class="citation book cs1">King, K. N. (2008). C Programming: A Modern Approach (2nd ed.). W. W. Norton & Company. p. 464. <a href="ISBN_(identifier)" class="mw-redirect" title="ISBN (identifier)">ISBN</a> <bdi>978-0393979503</bdi>.</cite>

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<li id="cite_note-14"><a href="#cite_ref-14">^</a> <cite id="CITEREFBader" class="citation web cs1">Bader, Dan. <a rel="nofollow" class="external text" href="https://dbader.org/blog/meaning-of-underscores-in-python">"The Meaning of Underscores in Python"</a>. Improve Your Python Skills. Retrieved 1 November 2019.</cite>

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<div class="mw-heading mw-heading2"><h2 id="References">References</h2></div>

<ul><li><cite id="CITEREFBloch2018" class="citation book cs1">Bloch, Joshua (2018). "Effective Java: Programming Language Guide" (third ed.). Addison-Wesley. <a href="ISBN_(identifier)" class="mw-redirect" title="ISBN (identifier)">ISBN</a> <bdi>978-0134685991</bdi>.</cite></li></ul></div><div><div class="zim-footer">

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