Inheritance (object-oriented programming) - Revision history

Polyphemus Goode: hatnote

2025-05-16T09:34:36Z

hatnote

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	{{Short description\|Process of deriving classes from, and organizing them into, a hierarchy}}		{{Short description\|Process of deriving classes from, and organizing them into, a hierarchy}}
			{{redirect\|Classical inheritance\|later inheritance of ancient culture\|classical tradition}}
	{{cleanup\|reason=Cluttered\|date=April 2015}}		{{cleanup\|reason=Cluttered\|date=April 2015}}
	In [[object-oriented programming]], '''inheritance''' is the mechanism of basing an [[Object (computer science)\|object]] or [[Class (computer programming)\|class]] upon another object ([[Prototype-based programming\|prototype-based inheritance]]) or class ([[Class-based programming\|class-based inheritance]]), retaining similar [[implementation]]. Also defined as deriving new classes ([[#Subclasses and superclasses\|sub classes]]) from existing ones such as super class or [[Fragile base class\|base class]] and then forming them into a hierarchy of classes. In most class-based object-oriented languages like [[C++]], an object created through inheritance, a "child object", acquires all the properties and behaviors of the "parent object", with the exception of: [[Constructor (object-oriented programming)\|constructors]], destructors, [[operator overloading\|overloaded operators]] and [[friend function]]s of the base class. Inheritance allows programmers to create classes that are built upon existing classes,<ref>{{cite web\|url=https://www.cse.msu.edu/~cse870/Input/SS2002/MiniProject/Sources/DRC.pdf \|title=Designing Reusable Classes \|last=Johnson \|first=Ralph \|date=August 26, 1991 \|website=www.cse.msu.edu }}</ref> to specify a new implementation while maintaining the same behaviors ([[Class diagram#Realization/Implementation\|realizing an interface]]), to reuse code and to independently extend original software via public classes and [[interface (object-oriented programming)\|interface]]s. The relationships of objects or classes through inheritance give rise to a [[directed acyclic graph]].		In [[object-oriented programming]], '''inheritance''' is the mechanism of basing an [[Object (computer science)\|object]] or [[Class (computer programming)\|class]] upon another object ([[Prototype-based programming\|prototype-based inheritance]]) or class ([[Class-based programming\|class-based inheritance]]), retaining similar [[implementation]]. Also defined as deriving new classes ([[#Subclasses and superclasses\|sub classes]]) from existing ones such as super class or [[Fragile base class\|base class]] and then forming them into a hierarchy of classes. In most class-based object-oriented languages like [[C++]], an object created through inheritance, a "child object", acquires all the properties and behaviors of the "parent object", with the exception of: [[Constructor (object-oriented programming)\|constructors]], destructors, [[operator overloading\|overloaded operators]] and [[friend function]]s of the base class. Inheritance allows programmers to create classes that are built upon existing classes,<ref>{{cite web\|url=https://www.cse.msu.edu/~cse870/Input/SS2002/MiniProject/Sources/DRC.pdf \|title=Designing Reusable Classes \|last=Johnson \|first=Ralph \|date=August 26, 1991 \|website=www.cse.msu.edu }}</ref> to specify a new implementation while maintaining the same behaviors ([[Class diagram#Realization/Implementation\|realizing an interface]]), to reuse code and to independently extend original software via public classes and [[interface (object-oriented programming)\|interface]]s. The relationships of objects or classes through inheritance give rise to a [[directed acyclic graph]].

65.206.123.158: /* Issues and alternatives */ small copy edit

2025-04-03T15:15:38Z

Issues and alternatives: small copy edit

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	==Issues and alternatives==		==Issues and alternatives==
	Implementation inheritance is controversial among programmers and theoreticians of object-oriented programming since at least the 1990s. Among ~~them~~ are the authors of ''[[Design Patterns]]'', who advocate interface inheritance ~~instead~~, and favor [[Composition over inheritance\|composition over inheritance]]. For example, the decorator pattern (as mentioned [[#Design constraints\|above]]) has been proposed to overcome the static nature of inheritance between classes. As a more fundamental solution to the same problem, [[role-oriented programming]] introduces a distinct relationship, ''played-by'', combining properties of inheritance and composition into a new concept.{{citation needed\|date=February 2016}}		Implementation inheritance has been controversial among programmers and theoreticians of object-oriented programming since at least the 1990s. Among the critics are the authors of ''[[Design Patterns]]'', who advocate instead for interface inheritance, and favor [[Composition over inheritance\|composition over inheritance]]. For example, the decorator pattern (as mentioned [[#Design constraints\|above]]) has been proposed to overcome the static nature of inheritance between classes. As a more fundamental solution to the same problem, [[role-oriented programming]] introduces a distinct relationship, ''played-by'', combining properties of inheritance and composition into a new concept.{{citation needed\|date=February 2016}}

	According to [[Allen Holub]], the main problem with implementation inheritance is that it introduces unnecessary [[Coupling (computer programming)\|coupling]] in the form of the [[Fragile base class\|"fragile base class problem"]]:{{r\|Mikhajlov}} modifications to the base class implementation can cause inadvertent behavioral changes in subclasses. Using interfaces avoids this problem because no implementation is shared, only the API.{{r\|holub}} Another way of stating this is that "inheritance breaks [[Encapsulation (object-oriented programming)\|encapsulation]]".<ref>{{Cite journal \|doi=10.1145/250707.239108 \|title=Evolution of object behavior using context relations \|journal=ACM SIGSOFT Software Engineering Notes \|volume=21 \|issue=6 \|page=46 \|year=1996 \|last1=Seiter \|first1=Linda M. \|last2=Palsberg \|first2=Jens \|last3=Lieberherr \|first3=Karl J. \|url=http://www.ccs.neu.edu/research/demeter/papers/context-journal/_context.html \|citeseerx=10.1.1.36.5053}}</ref> The problem surfaces clearly in open object-oriented systems such as [[Software framework\|frameworks]], where client code is expected to inherit from system-supplied classes and then substituted for the system's classes in its algorithms.{{r\|Mikhajlov}}		According to [[Allen Holub]], the main problem with implementation inheritance is that it introduces unnecessary [[Coupling (computer programming)\|coupling]] in the form of the [[Fragile base class\|"fragile base class problem"]]:{{r\|Mikhajlov}} modifications to the base class implementation can cause inadvertent behavioral changes in subclasses. Using interfaces avoids this problem because no implementation is shared, only the API.{{r\|holub}} Another way of stating this is that "inheritance breaks [[Encapsulation (object-oriented programming)\|encapsulation]]".<ref>{{Cite journal \|doi=10.1145/250707.239108 \|title=Evolution of object behavior using context relations \|journal=ACM SIGSOFT Software Engineering Notes \|volume=21 \|issue=6 \|page=46 \|year=1996 \|last1=Seiter \|first1=Linda M. \|last2=Palsberg \|first2=Jens \|last3=Lieberherr \|first3=Karl J. \|url=http://www.ccs.neu.edu/research/demeter/papers/context-journal/_context.html \|citeseerx=10.1.1.36.5053}}</ref> The problem surfaces clearly in open object-oriented systems such as [[Software framework\|frameworks]], where client code is expected to inherit from system-supplied classes and then substituted for the system's classes in its algorithms.{{r\|Mikhajlov}}

83.226.114.15: link to article

2025-01-24T21:09:11Z

link to article

← Previous revision		Revision as of 21:09, 24 January 2025
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	==Issues and alternatives==		==Issues and alternatives==
	Implementation inheritance is controversial among programmers and theoreticians of object-oriented programming since at least the 1990s. Among them are the authors of ''[[Design Patterns]]'', who advocate interface inheritance instead, and favor composition over inheritance. For example, the decorator pattern (as mentioned [[#Design constraints\|above]]) has been proposed to overcome the static nature of inheritance between classes. As a more fundamental solution to the same problem, [[role-oriented programming]] introduces a distinct relationship, ''played-by'', combining properties of inheritance and composition into a new concept.{{citation needed\|date=February 2016}}		Implementation inheritance is controversial among programmers and theoreticians of object-oriented programming since at least the 1990s. Among them are the authors of ''[[Design Patterns]]'', who advocate interface inheritance instead, and favor [[Composition over inheritance\|composition over inheritance]]. For example, the decorator pattern (as mentioned [[#Design constraints\|above]]) has been proposed to overcome the static nature of inheritance between classes. As a more fundamental solution to the same problem, [[role-oriented programming]] introduces a distinct relationship, ''played-by'', combining properties of inheritance and composition into a new concept.{{citation needed\|date=February 2016}}

	According to [[Allen Holub]], the main problem with implementation inheritance is that it introduces unnecessary [[Coupling (computer programming)\|coupling]] in the form of the [[Fragile base class\|"fragile base class problem"]]:{{r\|Mikhajlov}} modifications to the base class implementation can cause inadvertent behavioral changes in subclasses. Using interfaces avoids this problem because no implementation is shared, only the API.{{r\|holub}} Another way of stating this is that "inheritance breaks [[Encapsulation (object-oriented programming)\|encapsulation]]".<ref>{{Cite journal \|doi=10.1145/250707.239108 \|title=Evolution of object behavior using context relations \|journal=ACM SIGSOFT Software Engineering Notes \|volume=21 \|issue=6 \|page=46 \|year=1996 \|last1=Seiter \|first1=Linda M. \|last2=Palsberg \|first2=Jens \|last3=Lieberherr \|first3=Karl J. \|url=http://www.ccs.neu.edu/research/demeter/papers/context-journal/_context.html \|citeseerx=10.1.1.36.5053}}</ref> The problem surfaces clearly in open object-oriented systems such as [[Software framework\|frameworks]], where client code is expected to inherit from system-supplied classes and then substituted for the system's classes in its algorithms.{{r\|Mikhajlov}}		According to [[Allen Holub]], the main problem with implementation inheritance is that it introduces unnecessary [[Coupling (computer programming)\|coupling]] in the form of the [[Fragile base class\|"fragile base class problem"]]:{{r\|Mikhajlov}} modifications to the base class implementation can cause inadvertent behavioral changes in subclasses. Using interfaces avoids this problem because no implementation is shared, only the API.{{r\|holub}} Another way of stating this is that "inheritance breaks [[Encapsulation (object-oriented programming)\|encapsulation]]".<ref>{{Cite journal \|doi=10.1145/250707.239108 \|title=Evolution of object behavior using context relations \|journal=ACM SIGSOFT Software Engineering Notes \|volume=21 \|issue=6 \|page=46 \|year=1996 \|last1=Seiter \|first1=Linda M. \|last2=Palsberg \|first2=Jens \|last3=Lieberherr \|first3=Karl J. \|url=http://www.ccs.neu.edu/research/demeter/papers/context-journal/_context.html \|citeseerx=10.1.1.36.5053}}</ref> The problem surfaces clearly in open object-oriented systems such as [[Software framework\|frameworks]], where client code is expected to inherit from system-supplied classes and then substituted for the system's classes in its algorithms.{{r\|Mikhajlov}}

PaulTanenbaum: (1) Tidied up and (2) added that the inherits-from relation is a strict partial order

2024-12-04T14:49:55Z

(1) Tidied up and (2) added that the inherits-from relation is a strict partial order

← Previous revision		Revision as of 14:49, 4 December 2024
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	In [[object-oriented programming]], '''inheritance''' is the mechanism of basing an [[Object (computer science)\|object]] or [[Class (computer programming)\|class]] upon another object ([[Prototype-based programming\|prototype-based inheritance]]) or class ([[Class-based programming\|class-based inheritance]]), retaining similar [[implementation]]. Also defined as deriving new classes ([[#Subclasses and superclasses\|sub classes]]) from existing ones such as super class or [[Fragile base class\|base class]] and then forming them into a hierarchy of classes. In most class-based object-oriented languages like [[C++]], an object created through inheritance, a "child object", acquires all the properties and behaviors of the "parent object", with the exception of: [[Constructor (object-oriented programming)\|constructors]], destructors, [[operator overloading\|overloaded operators]] and [[friend function]]s of the base class. Inheritance allows programmers to create classes that are built upon existing classes,<ref>{{cite web\|url=https://www.cse.msu.edu/~cse870/Input/SS2002/MiniProject/Sources/DRC.pdf \|title=Designing Reusable Classes \|last=Johnson \|first=Ralph \|date=August 26, 1991 \|website=www.cse.msu.edu }}</ref> to specify a new implementation while maintaining the same behaviors ([[Class diagram#Realization/Implementation\|realizing an interface]]), to reuse code and to independently extend original software via public classes and [[interface (object-oriented programming)\|interface]]s. The relationships of objects or classes through inheritance give rise to a [[directed acyclic graph]].		In [[object-oriented programming]], '''inheritance''' is the mechanism of basing an [[Object (computer science)\|object]] or [[Class (computer programming)\|class]] upon another object ([[Prototype-based programming\|prototype-based inheritance]]) or class ([[Class-based programming\|class-based inheritance]]), retaining similar [[implementation]]. Also defined as deriving new classes ([[#Subclasses and superclasses\|sub classes]]) from existing ones such as super class or [[Fragile base class\|base class]] and then forming them into a hierarchy of classes. In most class-based object-oriented languages like [[C++]], an object created through inheritance, a "child object", acquires all the properties and behaviors of the "parent object", with the exception of: [[Constructor (object-oriented programming)\|constructors]], destructors, [[operator overloading\|overloaded operators]] and [[friend function]]s of the base class. Inheritance allows programmers to create classes that are built upon existing classes,<ref>{{cite web\|url=https://www.cse.msu.edu/~cse870/Input/SS2002/MiniProject/Sources/DRC.pdf \|title=Designing Reusable Classes \|last=Johnson \|first=Ralph \|date=August 26, 1991 \|website=www.cse.msu.edu }}</ref> to specify a new implementation while maintaining the same behaviors ([[Class diagram#Realization/Implementation\|realizing an interface]]), to reuse code and to independently extend original software via public classes and [[interface (object-oriented programming)\|interface]]s. The relationships of objects or classes through inheritance give rise to a [[directed acyclic graph]].

	An inherited class is called a '''subclass''' of its parent class or super class. The term "inheritance" is loosely used for both class-based and prototype-based programming, but in narrow use the term is reserved for class-based programming (one class ''inherits from'' another), with the corresponding technique in prototype-based programming being instead called ''[[Delegation (object-oriented programming)\|delegation]]'' (one object ''delegates to'' another). Class-modifying inheritance patterns can be pre-defined according to simple network interface parameters such that inter-language compatibility is preserved.<ref>{{cite book \|last1=Madsen \|first1=OL \|title=Conference proceedings on Object-oriented programming systems, languages and applications - OOPSLA '89 \|chapter=Virtual classes: A powerful mechanism in object-oriented programming \|date=1989\|pages=397–406 \|doi=10.1145/74877.74919 \|isbn=0897913337 \|s2cid=1104130 }}</ref><ref>{{cite book \|last1=Davies, Turk \|title=Advanced Methods and Deep Learning in Computer Vision \|date=2021 \|publisher=Elsevier Science \|pages=179–342}}</ref>		An inherited class is called a '''subclass''' of its parent class or super class. The term ''inheritance'' is loosely used for both class-based and prototype-based programming, but in narrow use the term is reserved for class-based programming (one class ''inherits from'' another), with the corresponding technique in prototype-based programming being instead called ''[[Delegation (object-oriented programming)\|delegation]]'' (one object ''delegates to'' another). Class-modifying inheritance patterns can be pre-defined according to simple network interface parameters such that inter-language compatibility is preserved.<ref>{{cite book \|last1=Madsen \|first1=OL \|title=Conference proceedings on Object-oriented programming systems, languages and applications - OOPSLA '89 \|chapter=Virtual classes: A powerful mechanism in object-oriented programming \|date=1989\|pages=397–406 \|doi=10.1145/74877.74919 \|isbn=0897913337 \|s2cid=1104130 }}</ref><ref>{{cite book \|last1=Davies, Turk \|title=Advanced Methods and Deep Learning in Computer Vision \|date=2021 \|publisher=Elsevier Science \|pages=179–342}}</ref>

	Inheritance should not be confused with [[subtyping]].<ref name=Cook90>{{Cite conference \|last1=Cook \|first1=William R. \|last2=Hill \|first2=Walter \|last3=Canning \|first3=Peter S. \|doi=10.1145/96709.96721 \|title=Inheritance is not subtyping \|conference=Proceedings of the 17th ACM SIGPLAN-SIGACT Symposium on Principles of Programming Languages (POPL) \|pages=125–135 \|year=1990 \|isbn=0-89791-343-4 \|citeseerx=10.1.1.102.8635}}</ref><ref>{{cite tech report \|first=Luca \|last=Cardelli \|title=Typeful Programming \|number=SRC Research Report 45 \|institution=[[Digital Equipment Corporation]] \|year=1993 \|page=32–33}}</ref> In some languages inheritance and subtyping agree,{{efn\|This is generally true only in statically-typed class-based OO languages, such as [[C++]], [[C Sharp (programming language)\|C#]], Java, and [[Scala (programming language)\|Scala]].}} whereas in others they differ; in general, subtyping establishes an [[is-a]] relationship, whereas inheritance only reuses implementation and establishes a syntactic relationship, not necessarily a semantic relationship (inheritance does not ensure behavioral subtyping). To distinguish these concepts, subtyping is sometimes referred to as ''interface inheritance'' (without acknowledging that the specialization of type variables also induces a subtyping relation), whereas inheritance as defined here is known as ''implementation inheritance'' or ''code inheritance''.<ref name="Mikhajlov">{{Cite conference \|doi=10.1007/BFb0054099 \|title=A study of the fragile base class problem \|conference=Proceedings of the 12th European Conference on Object-Oriented Programming (ECOOP) \|volume=1445 \|pages=355–382 \|series=Lecture Notes in Computer Science \|publisher=Springer \|year=1998 \|last1=Mikhajlov \|first1=Leonid \|last2=Sekerinski \|first2=Emil \|isbn=978-3-540-64737-9 \|url=http://extras.springer.com/2000/978-3-540-67660-7/papers/1445/14450355.pdf \|access-date=2015-08-28 \|archive-date=2017-08-13 \|archive-url=https://web.archive.org/web/20170813041125/http://extras.springer.com/2000/978-3-540-67660-7/papers/1445/14450355.pdf \|url-status=dead}}</ref> Still, inheritance is a commonly used mechanism for establishing subtype relationships.<ref>{{cite conference \|last1=Tempero \|first1=Ewan \|first2=Hong Yul \|last2=Yang \|first3=James \|last3=Noble \|title=What programmers do with inheritance in Java \|conference=ECOOP 2013–Object-Oriented Programming \|year= 2013 \|pages=577–601 \|url=https://www.cs.auckland.ac.nz/~ewan/qualitas/studies/inheritance/TemperoYangNobleECOOP2013-pre.pdf \|doi=10.1007/978-3-642-39038-8_24 \|isbn=978-3-642-39038-8 \|series=Lecture Notes in Computer Science \|volume=7920 \|publisher=Springer }}</ref>		Inheritance should not be confused with [[subtyping]].<ref name=Cook90>{{Cite conference \|last1=Cook \|first1=William R. \|last2=Hill \|first2=Walter \|last3=Canning \|first3=Peter S. \|doi=10.1145/96709.96721 \|title=Inheritance is not subtyping \|conference=Proceedings of the 17th ACM SIGPLAN-SIGACT Symposium on Principles of Programming Languages (POPL) \|pages=125–135 \|year=1990 \|isbn=0-89791-343-4 \|citeseerx=10.1.1.102.8635}}</ref><ref>{{cite tech report \|first=Luca \|last=Cardelli \|title=Typeful Programming \|number=SRC Research Report 45 \|institution=[[Digital Equipment Corporation]] \|year=1993 \|page=32–33}}</ref> In some languages inheritance and subtyping agree,{{efn\|This is generally true only in statically-typed class-based OO languages, such as [[C++]], [[C Sharp (programming language)\|C#]], Java, and [[Scala (programming language)\|Scala]].}} whereas in others they differ; in general, subtyping establishes an ''[[is-a]]'' relationship, whereas inheritance only reuses implementation and establishes a syntactic relationship, not necessarily a semantic relationship (inheritance does not ensure behavioral subtyping). To distinguish these concepts, subtyping is sometimes referred to as ''interface inheritance'' (without acknowledging that the specialization of type variables also induces a subtyping relation), whereas inheritance as defined here is known as ''implementation inheritance'' or ''code inheritance''.<ref name="Mikhajlov">{{Cite conference \|doi=10.1007/BFb0054099 \|title=A study of the fragile base class problem \|conference=Proceedings of the 12th European Conference on Object-Oriented Programming (ECOOP) \|volume=1445 \|pages=355–382 \|series=Lecture Notes in Computer Science \|publisher=Springer \|year=1998 \|last1=Mikhajlov \|first1=Leonid \|last2=Sekerinski \|first2=Emil \|isbn=978-3-540-64737-9 \|url=http://extras.springer.com/2000/978-3-540-67660-7/papers/1445/14450355.pdf \|access-date=2015-08-28 \|archive-date=2017-08-13 \|archive-url=https://web.archive.org/web/20170813041125/http://extras.springer.com/2000/978-3-540-67660-7/papers/1445/14450355.pdf \|url-status=dead}}</ref> Still, inheritance is a commonly used mechanism for establishing subtype relationships.<ref>{{cite conference \|last1=Tempero \|first1=Ewan \|first2=Hong Yul \|last2=Yang \|first3=James \|last3=Noble \|title=What programmers do with inheritance in Java \|conference=ECOOP 2013–Object-Oriented Programming \|year= 2013 \|pages=577–601 \|url=https://www.cs.auckland.ac.nz/~ewan/qualitas/studies/inheritance/TemperoYangNobleECOOP2013-pre.pdf \|doi=10.1007/978-3-642-39038-8_24 \|isbn=978-3-642-39038-8 \|series=Lecture Notes in Computer Science \|volume=7920 \|publisher=Springer }}</ref>

	Inheritance is contrasted with [[object composition]], where one object ''contains'' another object (or objects of one class contain objects of another class); see [[composition over inheritance]]. ~~Composition~~ ~~implements~~ a ~~[[has~~-a]] relationship, in ~~contrast~~ to ~~the is~~-a relationship ~~of subtyping~~.		Inheritance is contrasted with [[object composition]], where one object ''contains'' another object (or objects of one class contain objects of another class); see [[composition over inheritance]]. In contrast to subtyping’s ''is-a'' relationship, composition implements a ''[[has-a]]'' relationship.

			Mathematically speaking, inheritance in any system of classes induces a [[partially ordered set\|strict partial order]] on the set of classes in that system.

	== History ==		== History ==

Jerryobject: WP:REFerence WP:CITation parameters: respaces, reorders, update-standardize-conform, corrects, adds, fills. Small WP:COPYEDIT WP:EoS WP:TERSE: cut needless word repeat. WP:LINKs: add, update-standardize, needless WP:PIPE > WP:NOPIPE. MOS:COMMENT add.

2024-09-30T16:56:09Z

WP:REFerence WP:CITation parameters: respaces, reorders, update-standardize-conform, corrects, adds, fills. Small WP:COPYEDIT WP:EoS WP:TERSE: cut needless word repeat. WP:LINKs: add, update-standardize, needless WP:PIPE > WP:NOPIPE. MOS:COMMENT add.

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2024-09-07T07:52:04Z

Rescuing 2 sources and tagging 0 as dead.) #IABot (v2.0.9.5

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	[[File:Single Inheritance.jpg\|thumb\|upright\|Single inheritance]]		[[File:Single Inheritance.jpg\|thumb\|upright\|Single inheritance]]
	[[File:Multiple Inheritance.jpg\|thumb\|upright\|Multiple inheritance]]		[[File:Multiple Inheritance.jpg\|thumb\|upright\|Multiple inheritance]]
	There are various types of inheritance, based on paradigm and specific language.<ref>{{cite web\|url=https://www.cs.nmsu.edu/~rth/cs/cs177/map/inheritd.html\|title=C++ Inheritance\|website=www.cs.nmsu.edu}}</ref>		There are various types of inheritance, based on paradigm and specific language.<ref>{{cite web\|url=https://www.cs.nmsu.edu/~rth/cs/cs177/map/inheritd.html\|title=C++ Inheritance\|website=www.cs.nmsu.edu\|access-date=2018-05-16\|archive-date=2023-09-24\|archive-url=https://web.archive.org/web/20230924161416/https://www.cs.nmsu.edu/~rth/cs/cs177/map/inheritd.html\|url-status=dead}}</ref>

	;Single inheritance		;Single inheritance
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	According to [[Allen Holub]], the main problem with implementation inheritance is that it introduces unnecessary [[Coupling (computer programming)\|coupling]] in the form of the [[Fragile base class\|"fragile base class problem"]]:{{r\|Mikhajlov}} modifications to the base class implementation can cause inadvertent behavioral changes in subclasses. Using interfaces avoids this problem because no implementation is shared, only the API.{{r\|holub}} Another way of stating this is that "inheritance breaks [[Encapsulation (object-oriented programming)\|encapsulation]]".<ref>{{Cite journal \| doi = 10.1145/250707.239108\| title = Evolution of object behavior using context relations\| journal = ACM SIGSOFT Software Engineering Notes\| volume = 21\| issue = 6\| page = 46\| year = 1996\| last1 = Seiter \| first1 = Linda M.\| last2 = Palsberg \| first2 = Jens\| last3 = Lieberherr \| first3 = Karl J.\| url = http://www.ccs.neu.edu/research/demeter/papers/context-journal/_context.html\| citeseerx = 10.1.1.36.5053}}</ref> The problem surfaces clearly in open object-oriented systems such as [[Software framework\|frameworks]], where client code is expected to inherit from system-supplied classes and then substituted for the system's classes in its algorithms.{{r\|Mikhajlov}}		According to [[Allen Holub]], the main problem with implementation inheritance is that it introduces unnecessary [[Coupling (computer programming)\|coupling]] in the form of the [[Fragile base class\|"fragile base class problem"]]:{{r\|Mikhajlov}} modifications to the base class implementation can cause inadvertent behavioral changes in subclasses. Using interfaces avoids this problem because no implementation is shared, only the API.{{r\|holub}} Another way of stating this is that "inheritance breaks [[Encapsulation (object-oriented programming)\|encapsulation]]".<ref>{{Cite journal \| doi = 10.1145/250707.239108\| title = Evolution of object behavior using context relations\| journal = ACM SIGSOFT Software Engineering Notes\| volume = 21\| issue = 6\| page = 46\| year = 1996\| last1 = Seiter \| first1 = Linda M.\| last2 = Palsberg \| first2 = Jens\| last3 = Lieberherr \| first3 = Karl J.\| url = http://www.ccs.neu.edu/research/demeter/papers/context-journal/_context.html\| citeseerx = 10.1.1.36.5053}}</ref> The problem surfaces clearly in open object-oriented systems such as [[Software framework\|frameworks]], where client code is expected to inherit from system-supplied classes and then substituted for the system's classes in its algorithms.{{r\|Mikhajlov}}

	Reportedly, Java inventor [[James Gosling]] has spoken against implementation inheritance, stating that he would not include it if he were to redesign Java.<ref name="holub">{{cite web \|first=Allen \|last=Holub \|author-link=Allen Holub \|url=http://www.javaworld.com/article/2073649/core-java/why-extends-is-evil.html \|title=Why extends is evil \|date=1 August 2003 \|access-date=10 March 2015}}</ref> Language designs that decouple inheritance from subtyping (interface inheritance) appeared as early as 1990;<ref>{{Cite conference\| doi = 10.1007/BFb0019440\| title = Designing an object-oriented programming language with behavioural subtyping\| conference = REX School/Workshop on the Foundations of Object-Oriented Languages\| volume = 489\| pages = 60–90\| series = Lecture Notes in Computer Science\| year = 1991\| last1 = America \| first1 = Pierre\| isbn = 978-3-540-53931-5\| url = https://www.researchgate.net/publication/221501695}}</ref> a modern example of this is the [[Go (programming language)\|Go]] programming language.		Reportedly, Java inventor [[James Gosling]] has spoken against implementation inheritance, stating that he would not include it if he were to redesign Java.<ref name="holub">{{cite web \|first=Allen \|last=Holub \|author-link=Allen Holub \|url=http://www.javaworld.com/article/2073649/core-java/why-extends-is-evil.html \|title=Why extends is evil \|date=1 August 2003 \|access-date=10 March 2015 \|archive-date=24 February 2019 \|archive-url=https://web.archive.org/web/20190224073940/https://www.javaworld.com/article/2073649/core-java/why-extends-is-evil.html \|url-status=dead }}</ref> Language designs that decouple inheritance from subtyping (interface inheritance) appeared as early as 1990;<ref>{{Cite conference\| doi = 10.1007/BFb0019440\| title = Designing an object-oriented programming language with behavioural subtyping\| conference = REX School/Workshop on the Foundations of Object-Oriented Languages\| volume = 489\| pages = 60–90\| series = Lecture Notes in Computer Science\| year = 1991\| last1 = America \| first1 = Pierre\| isbn = 978-3-540-53931-5\| url = https://www.researchgate.net/publication/221501695}}</ref> a modern example of this is the [[Go (programming language)\|Go]] programming language.

	Complex inheritance, or inheritance used within an insufficiently mature design, may lead to the [[yo-yo problem]]. When inheritance was used as a primary approach to structure programs in the late 1990s, developers tended to break code into more layers of inheritance as the system functionality grew. If a development team combined multiple layers of inheritance with the single responsibility principle, this resulted in many very thin layers of code, with many layers consisting of only 1 or 2 lines of actual code.{{Citation needed\|date=October 2022}} Too many layers make debugging a significant challenge, as it becomes hard to determine which layer needs to be debugged.		Complex inheritance, or inheritance used within an insufficiently mature design, may lead to the [[yo-yo problem]]. When inheritance was used as a primary approach to structure programs in the late 1990s, developers tended to break code into more layers of inheritance as the system functionality grew. If a development team combined multiple layers of inheritance with the single responsibility principle, this resulted in many very thin layers of code, with many layers consisting of only 1 or 2 lines of actual code.{{Citation needed\|date=October 2022}} Too many layers make debugging a significant challenge, as it becomes hard to determine which layer needs to be debugged.

Graham87: mass-revert edits by user who often violates Wikipedia's Manual of Style; if you think the edit/s I have undone were an improvement, feel free to revert me

2023-12-28T04:44:16Z

mass-revert edits by user who often violates Wikipedia's Manual of Style; if you think the edit/s I have undone were an improvement, feel free to revert me

← Previous revision		Revision as of 04:44, 28 December 2023
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	== History ==		== History ==

	In 1966, [[Tony Hoare]] presented some remarks on records, and in particular presented the idea of record subclasses, record types with common properties but discriminated by a variant tag and having fields private to the variant.<ref>{{cite tech report \|last1=Hoare \|first1=C. A. R. \|title=Record Handling \|date=1966 \|url=http://archive.computerhistory.org/resources/text/Knuth_Don_X4100/PDF_index/k-9-pdf/k-9-u2293-Record-Handling-Hoare.pdf\|pages=15-16}}</ref> Influenced by this, in 1967, [[Ole-Johan Dahl]] and [[Kristen Nygaard]] presented a design that allowed specifying objects that belonged to different classes but had common properties. The common properties were collected in a superclass, and each superclass could itself potentially have a superclass. The values of a subclass were thus compound objects, consisting of some number of prefix parts belonging to various superclasses, plus a main part belonging to the subclass. These parts were all concatenated together.<ref>{{cite conference\|first1=Ole-Johan\|last1=Dahl\|first2=Kristen\|last2=Nygaard\|title=Class and subclass declarations\|publisher=Norwegian Computing Center\|conference=IFIP Working Conference on Simulation Languages\|place=Oslo\|date =May 1967\|url=https://www.ub.uio.no/fag/naturvitenskap-teknologi/informatikk/faglig/dns/dokumenter/classandsubclass1967.pdf}}</ref> The attributes of a compound object would be accessible by dot notation. This idea was first adopted in the [[Simula]] 67 programming language.<ref>{{cite book \|last1=Dahl \|first1=Ole-Johan \|chapter=The Birth of Object Orientation: the Simula Languages \|journal=From Object-Orientation to Formal Methods \|series=Lecture Notes in Computer Science \|date=2004 \|volume=2635 \|pages=15–25 \|doi=10.1007/978-3-540-39993-3_3 \|isbn=978-3-540-21366-6 \|chapter-url=https://www.mn.uio.no/ifi/english/about/ole-johan-dahl/bibliography/the-birth-of-object-orientation-the-simula-languages.pdf}}</ref> The idea then spread to [[Smalltalk]], [[C++]], [[Java (programming language)\|Java]], [[Python (programming language)\|Python]], and many other languages.		In 1966, [[Tony Hoare]] presented some remarks on records, and in particular presented the idea of record subclasses, record types with common properties but discriminated by a variant tag and having fields private to the variant.<ref>{{cite tech report \|last1=Hoare \|first1=C. A. R. \|title=Record Handling \|date=1966 \|url=http://archive.computerhistory.org/resources/text/Knuth_Don_X4100/PDF_index/k-9-pdf/k-9-u2293-Record-Handling-Hoare.pdf\|pages=15-16}}</ref> Influenced by this, in 1967 [[Ole-Johan Dahl]] and [[Kristen Nygaard]] presented a design that allowed specifying objects that belonged to different classes but had common properties. The common properties were collected in a superclass, and each superclass could itself potentially have a superclass. The values of a subclass were thus compound objects, consisting of some number of prefix parts belonging to various superclasses, plus a main part belonging to the subclass. These parts were all concatenated together.<ref>{{cite conference\|first1=Ole-Johan\|last1=Dahl\|first2=Kristen\|last2=Nygaard\|title=Class and subclass declarations\|publisher=Norwegian Computing Center\|conference=IFIP Working Conference on Simulation Languages\|place=Oslo\|date =May 1967\|url=https://www.ub.uio.no/fag/naturvitenskap-teknologi/informatikk/faglig/dns/dokumenter/classandsubclass1967.pdf}}</ref> The attributes of a compound object would be accessible by dot notation. This idea was first adopted in the [[Simula]] 67 programming language.<ref>{{cite book \|last1=Dahl \|first1=Ole-Johan \|chapter=The Birth of Object Orientation: the Simula Languages \|journal=From Object-Orientation to Formal Methods \|series=Lecture Notes in Computer Science \|date=2004 \|volume=2635 \|pages=15–25 \|doi=10.1007/978-3-540-39993-3_3 \|isbn=978-3-540-21366-6 \|chapter-url=https://www.mn.uio.no/ifi/english/about/ole-johan-dahl/bibliography/the-birth-of-object-orientation-the-simula-languages.pdf}}</ref> The idea then spread to [[Smalltalk]], [[C++]], [[Java (programming language)\|Java]], [[Python (programming language)\|Python]], and many other languages.

	==Types==		==Types==

Rager7: again comma posrt dates

2023-12-23T05:26:43Z

again comma posrt dates

← Previous revision		Revision as of 05:26, 23 December 2023
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	== History ==		== History ==

	In 1966, [[Tony Hoare]] presented some remarks on records, and in particular presented the idea of record subclasses, record types with common properties but discriminated by a variant tag and having fields private to the variant.<ref>{{cite tech report \|last1=Hoare \|first1=C. A. R. \|title=Record Handling \|date=1966 \|url=http://archive.computerhistory.org/resources/text/Knuth_Don_X4100/PDF_index/k-9-pdf/k-9-u2293-Record-Handling-Hoare.pdf\|pages=15-16}}</ref> Influenced by this, in 1967 [[Ole-Johan Dahl]] and [[Kristen Nygaard]] presented a design that allowed specifying objects that belonged to different classes but had common properties. The common properties were collected in a superclass, and each superclass could itself potentially have a superclass. The values of a subclass were thus compound objects, consisting of some number of prefix parts belonging to various superclasses, plus a main part belonging to the subclass. These parts were all concatenated together.<ref>{{cite conference\|first1=Ole-Johan\|last1=Dahl\|first2=Kristen\|last2=Nygaard\|title=Class and subclass declarations\|publisher=Norwegian Computing Center\|conference=IFIP Working Conference on Simulation Languages\|place=Oslo\|date =May 1967\|url=https://www.ub.uio.no/fag/naturvitenskap-teknologi/informatikk/faglig/dns/dokumenter/classandsubclass1967.pdf}}</ref> The attributes of a compound object would be accessible by dot notation. This idea was first adopted in the [[Simula]] 67 programming language.<ref>{{cite book \|last1=Dahl \|first1=Ole-Johan \|chapter=The Birth of Object Orientation: the Simula Languages \|journal=From Object-Orientation to Formal Methods \|series=Lecture Notes in Computer Science \|date=2004 \|volume=2635 \|pages=15–25 \|doi=10.1007/978-3-540-39993-3_3 \|isbn=978-3-540-21366-6 \|chapter-url=https://www.mn.uio.no/ifi/english/about/ole-johan-dahl/bibliography/the-birth-of-object-orientation-the-simula-languages.pdf}}</ref> The idea then spread to [[Smalltalk]], [[C++]], [[Java (programming language)\|Java]], [[Python (programming language)\|Python]], and many other languages.		In 1966, [[Tony Hoare]] presented some remarks on records, and in particular presented the idea of record subclasses, record types with common properties but discriminated by a variant tag and having fields private to the variant.<ref>{{cite tech report \|last1=Hoare \|first1=C. A. R. \|title=Record Handling \|date=1966 \|url=http://archive.computerhistory.org/resources/text/Knuth_Don_X4100/PDF_index/k-9-pdf/k-9-u2293-Record-Handling-Hoare.pdf\|pages=15-16}}</ref> Influenced by this, in 1967, [[Ole-Johan Dahl]] and [[Kristen Nygaard]] presented a design that allowed specifying objects that belonged to different classes but had common properties. The common properties were collected in a superclass, and each superclass could itself potentially have a superclass. The values of a subclass were thus compound objects, consisting of some number of prefix parts belonging to various superclasses, plus a main part belonging to the subclass. These parts were all concatenated together.<ref>{{cite conference\|first1=Ole-Johan\|last1=Dahl\|first2=Kristen\|last2=Nygaard\|title=Class and subclass declarations\|publisher=Norwegian Computing Center\|conference=IFIP Working Conference on Simulation Languages\|place=Oslo\|date =May 1967\|url=https://www.ub.uio.no/fag/naturvitenskap-teknologi/informatikk/faglig/dns/dokumenter/classandsubclass1967.pdf}}</ref> The attributes of a compound object would be accessible by dot notation. This idea was first adopted in the [[Simula]] 67 programming language.<ref>{{cite book \|last1=Dahl \|first1=Ole-Johan \|chapter=The Birth of Object Orientation: the Simula Languages \|journal=From Object-Orientation to Formal Methods \|series=Lecture Notes in Computer Science \|date=2004 \|volume=2635 \|pages=15–25 \|doi=10.1007/978-3-540-39993-3_3 \|isbn=978-3-540-21366-6 \|chapter-url=https://www.mn.uio.no/ifi/english/about/ole-johan-dahl/bibliography/the-birth-of-object-orientation-the-simula-languages.pdf}}</ref> The idea then spread to [[Smalltalk]], [[C++]], [[Java (programming language)\|Java]], [[Python (programming language)\|Python]], and many other languages.

	==Types==		==Types==

Citation bot: Alter: template type. Add: chapter-url, chapter. Removed or converted URL. Removed parameters. Some additions/deletions were parameter name changes. | Use this bot. Report bugs. | Suggested by Abductive | Category:Cleanup tagged articles with a reason field from April 2015 | #UCB_Category 35/39

2023-12-16T09:13:46Z

Alter: template type. Add: chapter-url, chapter. Removed or converted URL. Removed parameters. Some additions/deletions were parameter name changes. | Use this bot. Report bugs. | Suggested by Abductive | Category:Cleanup tagged articles with a reason field from April 2015 | #UCB_Category 35/39

← Previous revision		Revision as of 09:13, 16 December 2023
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	== History ==		== History ==

	In 1966, [[Tony Hoare]] presented some remarks on records, and in particular presented the idea of record subclasses, record types with common properties but discriminated by a variant tag and having fields private to the variant.<ref>{{cite tech report \|last1=Hoare \|first1=C. A. R. \|title=Record Handling \|date=1966 \|url=http://archive.computerhistory.org/resources/text/Knuth_Don_X4100/PDF_index/k-9-pdf/k-9-u2293-Record-Handling-Hoare.pdf\|pages=15-16}}</ref> Influenced by this, in 1967 [[Ole-Johan Dahl]] and [[Kristen Nygaard]] presented a design that allowed specifying objects that belonged to different classes but had common properties. The common properties were collected in a superclass, and each superclass could itself potentially have a superclass. The values of a subclass were thus compound objects, consisting of some number of prefix parts belonging to various superclasses, plus a main part belonging to the subclass. These parts were all concatenated together.<ref>{{cite conference\|first1=Ole-Johan\|last1=Dahl\|first2=Kristen\|last2=Nygaard\|title=Class and subclass declarations\|publisher=Norwegian Computing Center\|conference=IFIP Working Conference on Simulation Languages\|place=Oslo\|date =May 1967\|url=https://www.ub.uio.no/fag/naturvitenskap-teknologi/informatikk/faglig/dns/dokumenter/classandsubclass1967.pdf}}</ref> The attributes of a compound object would be accessible by dot notation. This idea was first adopted in the [[Simula]] 67 programming language.<ref>{{cite ~~journal~~ \|last1=Dahl \|first1=Ole-Johan \|~~title~~=The Birth of Object Orientation: the Simula Languages \|journal=From Object-Orientation to Formal Methods \|series=Lecture Notes in Computer Science \|date=2004 \|volume=2635 \|pages=15–25 \|doi=10.1007/978-3-540-39993-3_3 \|isbn=978-3-540-21366-6 \|url=https://www.mn.uio.no/ifi/english/about/ole-johan-dahl/bibliography/the-birth-of-object-orientation-the-simula-languages.pdf}}</ref> The idea then spread to [[Smalltalk]], [[C++]], [[Java (programming language)\|Java]], [[Python (programming language)\|Python]], and many other languages.		In 1966, [[Tony Hoare]] presented some remarks on records, and in particular presented the idea of record subclasses, record types with common properties but discriminated by a variant tag and having fields private to the variant.<ref>{{cite tech report \|last1=Hoare \|first1=C. A. R. \|title=Record Handling \|date=1966 \|url=http://archive.computerhistory.org/resources/text/Knuth_Don_X4100/PDF_index/k-9-pdf/k-9-u2293-Record-Handling-Hoare.pdf\|pages=15-16}}</ref> Influenced by this, in 1967 [[Ole-Johan Dahl]] and [[Kristen Nygaard]] presented a design that allowed specifying objects that belonged to different classes but had common properties. The common properties were collected in a superclass, and each superclass could itself potentially have a superclass. The values of a subclass were thus compound objects, consisting of some number of prefix parts belonging to various superclasses, plus a main part belonging to the subclass. These parts were all concatenated together.<ref>{{cite conference\|first1=Ole-Johan\|last1=Dahl\|first2=Kristen\|last2=Nygaard\|title=Class and subclass declarations\|publisher=Norwegian Computing Center\|conference=IFIP Working Conference on Simulation Languages\|place=Oslo\|date =May 1967\|url=https://www.ub.uio.no/fag/naturvitenskap-teknologi/informatikk/faglig/dns/dokumenter/classandsubclass1967.pdf}}</ref> The attributes of a compound object would be accessible by dot notation. This idea was first adopted in the [[Simula]] 67 programming language.<ref>{{cite book \|last1=Dahl \|first1=Ole-Johan \|chapter=The Birth of Object Orientation: the Simula Languages \|journal=From Object-Orientation to Formal Methods \|series=Lecture Notes in Computer Science \|date=2004 \|volume=2635 \|pages=15–25 \|doi=10.1007/978-3-540-39993-3_3 \|isbn=978-3-540-21366-6 \|chapter-url=https://www.mn.uio.no/ifi/english/about/ole-johan-dahl/bibliography/the-birth-of-object-orientation-the-simula-languages.pdf}}</ref> The idea then spread to [[Smalltalk]], [[C++]], [[Java (programming language)\|Java]], [[Python (programming language)\|Python]], and many other languages.

	==Types==		==Types==

HeyElliott: WP:N'T

2023-09-22T20:31:06Z

WP:N'T

← Previous revision		Revision as of 20:31, 22 September 2023
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	In some languages a class may be declared as [[Class (computer programming)#Non-subclassable\|non-subclassable]] by adding certain [[class modifier]]s to the class declaration. Examples include the <code>final</code> keyword in [[Final (Java)\|Java]] and [[C++11]] onwards or the <code>sealed</code> keyword in C#. Such modifiers are added to the class declaration before the <code>class</code> keyword and the class identifier declaration. Such non-subclassable classes restrict [[reusability]], particularly when developers only have access to precompiled [[Binary file\|binaries]] and not [[source code]].		In some languages a class may be declared as [[Class (computer programming)#Non-subclassable\|non-subclassable]] by adding certain [[class modifier]]s to the class declaration. Examples include the <code>final</code> keyword in [[Final (Java)\|Java]] and [[C++11]] onwards or the <code>sealed</code> keyword in C#. Such modifiers are added to the class declaration before the <code>class</code> keyword and the class identifier declaration. Such non-subclassable classes restrict [[reusability]], particularly when developers only have access to precompiled [[Binary file\|binaries]] and not [[source code]].

	A non-subclassable class has no subclasses, so it can be easily deduced at [[compile time]] that references or pointers to objects of that class are actually referencing instances of that class and not instances of subclasses (they ~~don't~~ exist) or instances of superclasses ([[upcasting]] a reference type violates the type system). Because the exact type of the object being referenced is known before execution, [[early binding]] (also called [[static dispatch]]) can be used instead of [[late binding]] (also called [[dynamic dispatch]]), which requires one or more [[virtual method table]] lookups depending on whether [[multiple inheritance]] or only [[single inheritance]] are supported in the programming language that is being used.		A non-subclassable class has no subclasses, so it can be easily deduced at [[compile time]] that references or pointers to objects of that class are actually referencing instances of that class and not instances of subclasses (they do not exist) or instances of superclasses ([[upcasting]] a reference type violates the type system). Because the exact type of the object being referenced is known before execution, [[early binding]] (also called [[static dispatch]]) can be used instead of [[late binding]] (also called [[dynamic dispatch]]), which requires one or more [[virtual method table]] lookups depending on whether [[multiple inheritance]] or only [[single inheritance]] are supported in the programming language that is being used.

	=== Non-overridable methods ===		=== Non-overridable methods ===

← Previous revision		Revision as of 09:34, 16 May 2025
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	{{Short description\|Process of deriving classes from, and organizing them into, a hierarchy}}		{{Short description\|Process of deriving classes from, and organizing them into, a hierarchy}}
			{{redirect\|Classical inheritance\|later inheritance of ancient culture\|classical tradition}}
	{{cleanup\|reason=Cluttered\|date=April 2015}}		{{cleanup\|reason=Cluttered\|date=April 2015}}
	In [[object-oriented programming]], '''inheritance''' is the mechanism of basing an [[Object (computer science)\|object]] or [[Class (computer programming)\|class]] upon another object ([[Prototype-based programming\|prototype-based inheritance]]) or class ([[Class-based programming\|class-based inheritance]]), retaining similar [[implementation]]. Also defined as deriving new classes ([[#Subclasses and superclasses\|sub classes]]) from existing ones such as super class or [[Fragile base class\|base class]] and then forming them into a hierarchy of classes. In most class-based object-oriented languages like [[C++]], an object created through inheritance, a "child object", acquires all the properties and behaviors of the "parent object", with the exception of: [[Constructor (object-oriented programming)\|constructors]], destructors, [[operator overloading\|overloaded operators]] and [[friend function]]s of the base class. Inheritance allows programmers to create classes that are built upon existing classes,<ref>{{cite web\|url=https://www.cse.msu.edu/~cse870/Input/SS2002/MiniProject/Sources/DRC.pdf \|title=Designing Reusable Classes \|last=Johnson \|first=Ralph \|date=August 26, 1991 \|website=www.cse.msu.edu }}</ref> to specify a new implementation while maintaining the same behaviors ([[Class diagram#Realization/Implementation\|realizing an interface]]), to reuse code and to independently extend original software via public classes and [[interface (object-oriented programming)\|interface]]s. The relationships of objects or classes through inheritance give rise to a [[directed acyclic graph]].		In [[object-oriented programming]], '''inheritance''' is the mechanism of basing an [[Object (computer science)\|object]] or [[Class (computer programming)\|class]] upon another object ([[Prototype-based programming\|prototype-based inheritance]]) or class ([[Class-based programming\|class-based inheritance]]), retaining similar [[implementation]]. Also defined as deriving new classes ([[#Subclasses and superclasses\|sub classes]]) from existing ones such as super class or [[Fragile base class\|base class]] and then forming them into a hierarchy of classes. In most class-based object-oriented languages like [[C++]], an object created through inheritance, a "child object", acquires all the properties and behaviors of the "parent object", with the exception of: [[Constructor (object-oriented programming)\|constructors]], destructors, [[operator overloading\|overloaded operators]] and [[friend function]]s of the base class. Inheritance allows programmers to create classes that are built upon existing classes,<ref>{{cite web\|url=https://www.cse.msu.edu/~cse870/Input/SS2002/MiniProject/Sources/DRC.pdf \|title=Designing Reusable Classes \|last=Johnson \|first=Ralph \|date=August 26, 1991 \|website=www.cse.msu.edu }}</ref> to specify a new implementation while maintaining the same behaviors ([[Class diagram#Realization/Implementation\|realizing an interface]]), to reuse code and to independently extend original software via public classes and [[interface (object-oriented programming)\|interface]]s. The relationships of objects or classes through inheritance give rise to a [[directed acyclic graph]].

← Previous revision		Revision as of 07:52, 7 September 2024
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	[[File:Single Inheritance.jpg\|thumb\|upright\|Single inheritance]]		[[File:Single Inheritance.jpg\|thumb\|upright\|Single inheritance]]
	[[File:Multiple Inheritance.jpg\|thumb\|upright\|Multiple inheritance]]		[[File:Multiple Inheritance.jpg\|thumb\|upright\|Multiple inheritance]]
	There are various types of inheritance, based on paradigm and specific language.<ref>{{cite web\|url=https://www.cs.nmsu.edu/~rth/cs/cs177/map/inheritd.html\|title=C++ Inheritance\|website=www.cs.nmsu.edu}}</ref>		There are various types of inheritance, based on paradigm and specific language.<ref>{{cite web\|url=https://www.cs.nmsu.edu/~rth/cs/cs177/map/inheritd.html\|title=C++ Inheritance\|website=www.cs.nmsu.edu\|access-date=2018-05-16\|archive-date=2023-09-24\|archive-url=https://web.archive.org/web/20230924161416/https://www.cs.nmsu.edu/~rth/cs/cs177/map/inheritd.html\|url-status=dead}}</ref>

	;Single inheritance		;Single inheritance
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	According to [[Allen Holub]], the main problem with implementation inheritance is that it introduces unnecessary [[Coupling (computer programming)\|coupling]] in the form of the [[Fragile base class\|"fragile base class problem"]]:{{r\|Mikhajlov}} modifications to the base class implementation can cause inadvertent behavioral changes in subclasses. Using interfaces avoids this problem because no implementation is shared, only the API.{{r\|holub}} Another way of stating this is that "inheritance breaks [[Encapsulation (object-oriented programming)\|encapsulation]]".<ref>{{Cite journal \| doi = 10.1145/250707.239108\| title = Evolution of object behavior using context relations\| journal = ACM SIGSOFT Software Engineering Notes\| volume = 21\| issue = 6\| page = 46\| year = 1996\| last1 = Seiter \| first1 = Linda M.\| last2 = Palsberg \| first2 = Jens\| last3 = Lieberherr \| first3 = Karl J.\| url = http://www.ccs.neu.edu/research/demeter/papers/context-journal/_context.html\| citeseerx = 10.1.1.36.5053}}</ref> The problem surfaces clearly in open object-oriented systems such as [[Software framework\|frameworks]], where client code is expected to inherit from system-supplied classes and then substituted for the system's classes in its algorithms.{{r\|Mikhajlov}}		According to [[Allen Holub]], the main problem with implementation inheritance is that it introduces unnecessary [[Coupling (computer programming)\|coupling]] in the form of the [[Fragile base class\|"fragile base class problem"]]:{{r\|Mikhajlov}} modifications to the base class implementation can cause inadvertent behavioral changes in subclasses. Using interfaces avoids this problem because no implementation is shared, only the API.{{r\|holub}} Another way of stating this is that "inheritance breaks [[Encapsulation (object-oriented programming)\|encapsulation]]".<ref>{{Cite journal \| doi = 10.1145/250707.239108\| title = Evolution of object behavior using context relations\| journal = ACM SIGSOFT Software Engineering Notes\| volume = 21\| issue = 6\| page = 46\| year = 1996\| last1 = Seiter \| first1 = Linda M.\| last2 = Palsberg \| first2 = Jens\| last3 = Lieberherr \| first3 = Karl J.\| url = http://www.ccs.neu.edu/research/demeter/papers/context-journal/_context.html\| citeseerx = 10.1.1.36.5053}}</ref> The problem surfaces clearly in open object-oriented systems such as [[Software framework\|frameworks]], where client code is expected to inherit from system-supplied classes and then substituted for the system's classes in its algorithms.{{r\|Mikhajlov}}

	Reportedly, Java inventor [[James Gosling]] has spoken against implementation inheritance, stating that he would not include it if he were to redesign Java.<ref name="holub">{{cite web \|first=Allen \|last=Holub \|author-link=Allen Holub \|url=http://www.javaworld.com/article/2073649/core-java/why-extends-is-evil.html \|title=Why extends is evil \|date=1 August 2003 \|access-date=10 March 2015}}</ref> Language designs that decouple inheritance from subtyping (interface inheritance) appeared as early as 1990;<ref>{{Cite conference\| doi = 10.1007/BFb0019440\| title = Designing an object-oriented programming language with behavioural subtyping\| conference = REX School/Workshop on the Foundations of Object-Oriented Languages\| volume = 489\| pages = 60–90\| series = Lecture Notes in Computer Science\| year = 1991\| last1 = America \| first1 = Pierre\| isbn = 978-3-540-53931-5\| url = https://www.researchgate.net/publication/221501695}}</ref> a modern example of this is the [[Go (programming language)\|Go]] programming language.		Reportedly, Java inventor [[James Gosling]] has spoken against implementation inheritance, stating that he would not include it if he were to redesign Java.<ref name="holub">{{cite web \|first=Allen \|last=Holub \|author-link=Allen Holub \|url=http://www.javaworld.com/article/2073649/core-java/why-extends-is-evil.html \|title=Why extends is evil \|date=1 August 2003 \|access-date=10 March 2015 \|archive-date=24 February 2019 \|archive-url=https://web.archive.org/web/20190224073940/https://www.javaworld.com/article/2073649/core-java/why-extends-is-evil.html \|url-status=dead }}</ref> Language designs that decouple inheritance from subtyping (interface inheritance) appeared as early as 1990;<ref>{{Cite conference\| doi = 10.1007/BFb0019440\| title = Designing an object-oriented programming language with behavioural subtyping\| conference = REX School/Workshop on the Foundations of Object-Oriented Languages\| volume = 489\| pages = 60–90\| series = Lecture Notes in Computer Science\| year = 1991\| last1 = America \| first1 = Pierre\| isbn = 978-3-540-53931-5\| url = https://www.researchgate.net/publication/221501695}}</ref> a modern example of this is the [[Go (programming language)\|Go]] programming language.

	Complex inheritance, or inheritance used within an insufficiently mature design, may lead to the [[yo-yo problem]]. When inheritance was used as a primary approach to structure programs in the late 1990s, developers tended to break code into more layers of inheritance as the system functionality grew. If a development team combined multiple layers of inheritance with the single responsibility principle, this resulted in many very thin layers of code, with many layers consisting of only 1 or 2 lines of actual code.{{Citation needed\|date=October 2022}} Too many layers make debugging a significant challenge, as it becomes hard to determine which layer needs to be debugged.		Complex inheritance, or inheritance used within an insufficiently mature design, may lead to the [[yo-yo problem]]. When inheritance was used as a primary approach to structure programs in the late 1990s, developers tended to break code into more layers of inheritance as the system functionality grew. If a development team combined multiple layers of inheritance with the single responsibility principle, this resulted in many very thin layers of code, with many layers consisting of only 1 or 2 lines of actual code.{{Citation needed\|date=October 2022}} Too many layers make debugging a significant challenge, as it becomes hard to determine which layer needs to be debugged.