Object-oriented programming: Difference between revisions

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[[File:oop-uml-class-example.png|frame|right|[[Unified Modeling Language|UML]] notation for a class. This Button class has [[Variable (computer science)|variables]] for data, and [[Method (computer programming)|functions]]. Through inheritance a subclass can be created as subset of the Button class. Objects are instances of a class.]]

Terminology invoking "objects" and "oriented" in the modern sense of object-oriented programming made its first appearance at [[MIT]] in the late 1950s and early 1960s. In the environment of the [[artificial intelligence]] group, as early as 1960, "object" could refer to identified items ([[Lisp (programming language)|LISP]] atoms) with properties (attributes);<ref>{{Cite journal

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[[Alan Kay]] later cited a detailed understanding of LISP internals as a strong influence on his thinking in 1966, and that he used the term "object-oriented programming" in conversation as early as 1967.<ref name=alanKayOnOO/> Although sometimes called "the father of object-oriented programming",<ref>{{cite book |last1=Butcher |first1=Paul |title=Seven Concurrency Models in Seven Weeks: When Threads Unravel |date=30 June 2014 |publisher=Pragmatic Bookshelf |isbn=978-1-68050-466-8 |page=204 |url=https://www.google.com/books/edition/Seven_Concurrency_Models_in_Seven_Weeks/Xg9QDwAAQBAJ?hl=en&gbpv=1&pg=PT204 |language=en}}</ref> Alan Kay has differentiated his notion of OO from the more conventional [[abstract data type]] notion of object, and has implied that the computer science establishment did not adopt his notion.<ref name=alanKayOnOO>{{Cite web|url= http://www.purl.org/stefan_ram/pub/doc_kay_oop_en |title=Dr. Alan Kay on the Meaning of "Object-Oriented Programming" |year= 2003|access-date=11 February 2010}}</ref> A 1976 MIT memo co-authored by [[Barbara Liskov]] lists [[Simula 67]], [[CLU (programming language)|CLU]], and [[Alphard (programming language)|Alphard]] as object-oriented languages, but does not mention Smalltalk.<ref>{{cite tech report |last=Jones |first=Anita K. |last2=Liskov|first2=Barbara H. |date=April 1976 |title=An Access Control Facility for Programming Languages |institution=MIT |number=CSG Memo 137|url=http://csg.csail.mit.edu/CSGArchives/memos/Memo-137.pdf }}</ref>

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In the 1970s, the first version of the [[Smalltalk]] programming language was developed at [[Xerox PARC]] by [[Alan Kay]], [[Dan Ingalls]] and [[Adele Goldberg (computer scientist)|Adele Goldberg]]. Smalltalk-72 included a programming environment and was [[Dynamic programming|dynamically typed]], and at first was [[Interpreter (computing)|interpreted]], not [[Compiler|compiled]]. Smalltalk became noted for its application of object orientation at the language-level and its graphical development environment. Smalltalk went through various versions and interest in the language grew.<ref name="Bertrand Meyer 2009 329">{{Cite book|title=Touch of Class: Learning to Program Well with Objects and Contracts|author=Bertrand Meyer|publisher=Springer Science & Business Media|year=2009|isbn=978-3-540-92144-8|pages=329|bibcode=2009tclp.book.....M}}</ref> While [[Smalltalk]] was influenced by the ideas introduced in Simula 67 it was designed to be a fully dynamic system in which classes could be created and modified dynamically.<ref name="st">{{Cite web|first=Alan |last=Kay |url=http://gagne.homedns.org/~tgagne/contrib/EarlyHistoryST.html |title=The Early History of Smalltalk |access-date=13 September 2007 |url-status=dead |archive-url=https://web.archive.org/web/20080710144930/http://gagne.homedns.org/~tgagne/contrib/EarlyHistoryST.html |archive-date=10 July 2008 }}</ref>

In the 1970s, Smalltalk influenced the [[Lisp (programming language)#Language innovations|Lisp community]] to incorporate [[Lisp (programming language)#Object systems|object-based techniques]] that were introduced to developers via the [[Lisp machine]].{{cn|reason=The dates don't line up, Flavors is 1982 and LOOPS is 1983 so they were most likely influenced by Smalltalk-80}} Experimentation with various extensions to Lisp (such as LOOPS and [[Flavors (programming language)|Flavors]] introducing [[multiple inheritance]] and [[mixins]]) eventually led to the [[Common Lisp Object System]], which integrates functional programming and object-oriented programming and allows extension via a [[Meta-object protocol]]. In the 1980s, there were a few attempts to design processor architectures that included hardware support for objects in memory but these were not successful. Examples include the [[Intel iAPX 432]] and the [[Linn Products|Linn Smart]] [[Rekursiv]].

In 1981, Goldberg edited the August issue of [[Byte Magazine]], introducing Smalltalk and object-oriented programming to a wider audience. In 1986, the [[Association for Computing Machinery]] organised the first ''Conference on Object-Oriented Programming, Systems, Languages, and Applications'' (OOPSLA), which was unexpectedly attended by 1,000 people. In the mid-1980s [[Objective-C]] was developed by [[Brad Cox]], who had used Smalltalk at [[ITT Inc.]], and [[Bjarne Stroustrup]], who had used Simula for his PhD thesis, eventually went to create the object-oriented [[C++]].<ref name="Bertrand Meyer 2009 329"/> In 1985, [[Bertrand Meyer]] also produced the first design of the [[Eiffel (programming language)|Eiffel language]]. Focused on software quality, Eiffel is a purely object-oriented programming language and a notation supporting the entire software lifecycle. Meyer described the Eiffel software development method, based on a small number of key ideas from software engineering and computer science, in [[Object-Oriented Software Construction]]. Essential to the quality focus of Eiffel is Meyer's reliability mechanism, [[Design by Contract]], which is an integral part of both the method and language.