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98-537: Object-oriented programming ( OOP ) is a programming paradigm based on the concept of objects , which can contain data and code : data in the form of fields (often known as attributes or properties ), and code in the form of procedures (often known as methods ). In OOP, computer programs are designed by making them out of objects that interact with one another. Many of the most widely used programming languages (such as C++ , Java , and Python ) are multi-paradigm and support object-oriented programming to

196-585: A computer programmer after passing an aptitude test. After his discharge, he enrolled at the University of Colorado Boulder and earned a Bachelor of Science (B.S.) in mathematics and molecular biology in 1966. In the autumn of 1966, he began graduate school at the University of Utah College of Engineering . He earned a Master of Science in electrical engineering in 1968, then a Doctor of Philosophy in computer science in 1969. His doctoral dissertation, FLEX: A Flexible Extendable Language , described

294-433: A consequence, no one parallel programming language maps well to all computation problems. Thus, it is more convenient to use a base sequential language and insert API calls to parallel execution models via a programming model. Such parallel programming models can be classified according to abstractions that reflect the hardware, such as shared memory , distributed memory with message passing , notions of place visible in

392-476: A different point in time inside a different unit of code. The communication between the units of code is not explicit. In contrast, languages in the declarative paradigm do not state the order in which to execute operations. Instead, they supply a number of available operations in the system, along with the conditions under which each is allowed to execute. The implementation of the language's execution model tracks which operations are free to execute and chooses

490-786: A distinctive approach to object orientation, classes, and such. Inheritance is not obvious in Wirth's design since his nomenclature looks in the opposite direction: It is called type extension and the viewpoint is from the parent down to the inheritor. Object-oriented features have been added to many previously existing languages, including Ada , BASIC , Fortran , Pascal , and COBOL . Adding these features to languages that were not initially designed for them often led to problems with compatibility and maintainability of code. More recently, some languages have emerged that are primarily object-oriented, but that are also compatible with procedural methodology. Two such languages are Python and Ruby . Probably

588-410: A form of imperative programming , structures programs as a human-centered web, as in a hypertext essay: documentation is integral to the program, and the program is structured following the logic of prose exposition, rather than compiler convenience. Symbolic techniques such as reflection , which allow the program to refer to itself, might also be considered as a programming paradigm. However, this

686-430: A form of polymorphism – is when calling code can be independent of which class in the supported hierarchy it is operating on – the parent class or one of its descendants. Meanwhile, the same operation name among objects in an inheritance hierarchy may behave differently. For example, objects of the type Circle and Square are derived from a common class called Shape. The Draw function for each type of Shape implements what

784-482: A fruit if the object fruit exists, and both apple and orange have fruit as their prototype. The idea of the fruit class does not exist explicitly, but can be modeled as the equivalence class of the objects sharing the same prototype, or as the set of objects satisfying a certain interface ( duck typing ). Unlike class-based programming, it is typically possible in prototype-based languages to define attributes and methods not shared with other objects; for example,

882-402: A given type or class of object. Objects are created by calling a special type of method in the class known as a constructor . Classes may inherit from other classes, so they are arranged in a hierarchy that represents "is-a-type-of" relationships. For example, class Employee might inherit from class Person. All the data and methods available to the parent class also appear in the child class with

980-528: A greater or lesser degree, typically in combination with imperative programming , procedural programming and functional programming . Significant object-oriented languages include Ada , ActionScript , C++ , Common Lisp , C# , Dart , Eiffel , Fortran 2003 , Haxe , Java , JavaScript , Kotlin , Logo , MATLAB , Objective-C , Object Pascal , Perl , PHP , Python , R , Raku , Ruby , Scala , SIMSCRIPT , Simula , Smalltalk , Swift , Vala and Visual Basic.NET . Terminology invoking "objects" in

1078-485: A mixin is simply a class that does not represent an is-a-type-of relationship. Mixins are typically used to add the same methods to multiple classes. For example, class UnicodeConversionMixin might provide a method unicode_to_ascii() when included in class FileReader and class WebPageScraper, which do not share a common parent. Abstract classes cannot be instantiated into objects; they exist only for inheritance into other "concrete" classes that can be instantiated. In Java,

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1176-579: A network, only able to communicate with messages (so messaging came at the very beginning – it took a while to see how to do messaging in a programming language efficiently enough to be useful). Alan Kay, Influenced by the work at MIT and the Simula language, in November 1966 Alan Kay began working on ideas that would eventually be incorporated into the Smalltalk programming language. Kay used

1274-549: A professorship at Carnegie Mellon University . Instead, in 1970, he joined the Xerox PARC research staff in Palo Alto, California . Through the decade, he developed prototypes of networked workstations using the programming language Smalltalk . Along with some colleagues at PARC, Kay is one of the fathers of the idea of object-oriented programming (OOP), which he named. Some original object-oriented concepts, including

1372-471: A program written in C++ , Object Pascal , or PHP can be purely procedural , purely object-oriented , or can contain aspects of both paradigms, or others. When using a language that supports multiple paradigms, the developer chooses which paradigm elements to use. But, this choice may not involve considering paradigms per se. The developer often uses the features of a language as the language provides them and to

1470-625: A senior fellow, departing when HP disbanded the Advanced Software Research Team on July 20, 2005. He has been an adjunct professor of computer science at the University of California, Los Angeles , a visiting professor at Kyoto University , and an adjunct professor at the Massachusetts Institute of Technology (MIT). Kay served on the advisory board of TTI/Vanguard . In December 1995, while still at Apple, Kay collaborated with many others to start

1568-454: A separate location addressed via a pointer). Date and Darwen have proposed a theoretical foundation that uses OOP as a kind of customizable type system to support RDBMS , but it forbids object pointers. The OOP paradigm has been criticized for overemphasizing the use of objects for software design and modeling at the expense of other important aspects (computation/algorithms). For example, Rob Pike has said that OOP languages frequently shift

1666-459: A sequence of stateless function evaluations. When programming computers or systems with many processors, in process-oriented programming , programs are treated as sets of concurrent processes that act on a logical shared data structures . Many programming paradigms are as well known for the techniques they forbid as for those they support . For instance, pure functional programming disallows side-effects , while structured programming disallows

1764-421: A special name such as this or self used to refer to the current object. In languages that support open recursion , object methods can call other methods on the same object (including themselves) using this name. This variable is late-bound ; it allows a method defined in one class to invoke another method that is defined later, in some subclass thereof. Simula (1967) is generally accepted as being

1862-435: A strangely skewed perspective. Rich Hickey , creator of Clojure , described object systems as overly simplistic models of the real world. He emphasized the inability of OOP to model time properly, which is getting increasingly problematic as software systems become more concurrent. Alexander Stepanov compares object orientation unfavourably to generic programming : I find OOP technically unsound. It attempts to decompose

1960-693: Is class-based , but to users (during programming) it acts as if it were prototype-based . Tweak objects are created and run in Tweak project windows. In November 2005, at the World Summit on the Information Society , the MIT research laboratories unveiled a new laptop computer for educational use around the world. It has many names, including the $ 100 Laptop, the One Laptop per Child program,

2058-448: Is delegated to its parent object or class, and so on, going up the chain of inheritance. Data abstraction is a design pattern in which data are visible only to semantically related functions, to prevent misuse. The success of data abstraction leads to frequent incorporation of data hiding as a design principle in object-oriented and pure functional programming. Similarly, encapsulation prevents external code from being concerned with

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2156-550: Is a paradigm that describes programs able to manipulate formulas and program components as data. Programs can thus effectively modify themselves, and appear to "learn", making them suited for applications such as artificial intelligence , expert systems , natural-language processing and computer games. Languages that support this paradigm include Lisp and Prolog . Differentiable programming structures programs so that they can be differentiated throughout, usually via automatic differentiation . Literate programming , as

2254-493: Is a technique that encourages decoupling . In object oriented programming, objects provide a layer which can be used to separate internal from external code and implement abstraction and encapsulation. External code can only use an object by calling a specific instance method with a certain set of input parameters, reading an instance variable, or writing to an instance variable. A program may create many instances of objects as it runs, which operate independently. This technique, it

2352-402: Is also a form of information hiding. Some languages (Java, for example) let classes enforce access restrictions explicitly, for example, denoting internal data with the private keyword and designating methods intended for use by code outside the class with the public keyword. Methods may also be designed public, private, or intermediate levels such as protected (which allows access from

2450-537: Is also the architect of the modern overlapping windowing graphical user interface (GUI). Because the Dynabook was conceived as an educational platform, he is considered one of the first researchers into mobile learning ; many features of the Dynabook concept have been adopted in the design of the One Laptop Per Child educational platform, with which Kay is actively involved. From 1981 to 1984, Kay

2548-405: Is called (i.e. at least one other parameter object is involved in the method choice), one speaks of multiple dispatch . A method call is also known as message passing . It is conceptualized as a message (the name of the method and its input parameters) being passed to the object for dispatch. Dispatch interacts with inheritance; if a method is not present in a given object or class, the dispatch

2646-513: Is claimed, allows easy re-use of the same procedures and data definitions for different sets of data, in addition to potentially mirroring real-world relationships intuitively. Rather than utilizing database tables and programming subroutines, the developer utilizes objects the user may be more familiar with: objects from their application domain. These claims that the OOP paradigm enhances reusability and modularity have been criticized. The initial design

2744-400: Is classified as imperative and is sometimes called the second-generation programming language . In the 1960s, assembly languages were developed to support library COPY and quite sophisticated conditional macro generation and preprocessing abilities, CALL to subroutine , external variables and common sections (globals), enabling significant code re-use and isolation from hardware specifics via

2842-441: Is compatible with the major paradigms and thus is not a real paradigm in its own right. Alan Kay Alan Curtis Kay (born May 17, 1940) is an American computer scientist best known for his pioneering work on object-oriented programming and windowing graphical user interface (GUI) design. At Xerox PARC he led the design and development of the first modern windowed computer desktop interface. There he also led

2940-519: Is difficult because of lack of an agreed-upon and rigorous definition of OOP. Modular programming support provides the ability to group procedures into files and modules for organizational purposes. Modules are namespaced so identifiers in one module will not conflict with a procedure or variable sharing the same name in another file or module. An object is a data structure or abstract data type containing fields (state variables containing data) and methods ( subroutines or procedures defining

3038-428: Is encouraged to use the most restrictive visibility possible, in order of local (or method) variables, private variables (in object oriented programming), and global (or public) variables, and only be expanded when and as much as necessary. This prevents changes to visibility from invalidating existing code. If a class does not allow calling code to access internal object data and permits access through methods only, this

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3136-564: Is known as object composition . For example, an object in the Employee class might contain (either directly or through a pointer) an object in the Address class, in addition to its own instance variables like "first_name" and "position". Object composition is used to represent "has-a" relationships: every employee has an address, so every Employee object has access to a place to store an Address object (either directly embedded within itself or at

3234-408: Is necessary to draw itself while calling code can remain indifferent to the particular type of Shape being drawn. This is another type of abstraction that simplifies code external to the class hierarchy and enables strong separation of concerns . A common feature of objects is that methods are attached to them and can access and modify the object's data fields. In this brand of OOP, there is usually

3332-447: Is quoted as saying: The problem with object-oriented languages is they've got all this implicit environment that they carry around with them. You wanted a banana but what you got was a gorilla holding the banana and the entire jungle. Leo Brodie has suggested a connection between the standalone nature of objects and a tendency to duplicate code in violation of the don't repeat yourself principle of software development. Subtyping –

3430-633: The final keyword can be used to prevent a class from being subclassed. In contrast, in prototype-based programming , objects are the primary entities. Generally, the concept of a "class" does not even exist. Rather, the prototype or parent of an object is just another object to which the object is linked. In Self, an object may have multiple or no parents, but in the most popular prototype-based language, Javascript, every object has one prototype link (and only one). New objects can be created based on already existing objects chosen as their prototype. You may call two different objects apple and orange

3528-425: The C programming language . The " open/closed principle " advocates that classes and functions "should be open for extension, but closed for modification". Luca Cardelli has claimed that OOP languages have "extremely poor modularity properties with respect to class extension and modification", and tend to be extremely complex. The latter point is reiterated by Joe Armstrong , the principal inventor of Erlang , who

3626-583: The Cocoa frameworks on Mac OS X , written in Objective-C , an object-oriented, dynamic messaging extension to C based on Smalltalk. OOP toolkits also enhanced the popularity of event-driven programming (although this concept is not limited to OOP). At ETH Zürich , Niklaus Wirth and his colleagues investigated the concept of type checking across module boundaries. Modula-2 (1978) included this concept, and their succeeding design, Oberon (1987), included

3724-530: The Defense Advanced Research Projects Agency (DARPA), he ended his musical career. In 1968, he met Seymour Papert and learned of the programming language Logo , a dialect of Lisp optimized for educational purposes. This led him to learn of the work of Jean Piaget , Jerome Bruner , Lev Vygotsky , and of constructionist learning , further influencing his professional orientation. On December 9 of that same year he

3822-540: The Linn Smart Rekursiv . In the mid-1980s Objective-C was developed by Brad Cox , who had used Smalltalk at ITT Inc. . Bjarne Stroustrup , who had used Simula for his PhD thesis, created the object-oriented C++ . In 1985, Bertrand Meyer also produced the first design of the Eiffel language . Focused on software quality, Eiffel is a purely object-oriented programming language and a notation supporting

3920-743: The New York metropolitan area . He attended Brooklyn Technical High School . Having accumulated enough credits to graduate, he then attended Bethany College in Bethany, West Virginia , where he majored in biology and minored in mathematics. Kay then taught guitar in Denver , Colorado for a year. He was drafted in the United States Army , then qualified for officer training in the United States Air Force , where he became

4018-566: The execution model , such as allowing side effects , or whether the sequence of operations is defined by the execution model. Other paradigms are about the way code is organized, such as grouping into units that include both state and behavior. Yet others are about syntax and grammar . Some common programming paradigms include (shown in hierarchical relationship): Programming paradigms come from computer science research into existing practices of software development . The findings allow for describing and comparing programming practices and

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4116-497: The goto construct. Partly for this reason, new paradigms are often regarded as doctrinaire or overly rigid by those accustomed to older ones. Yet, avoiding certain techniques can make it easier to understand program behavior, and to prove theorems about program correctness. Programming paradigms can also be compared with programming models , which allows invoking an execution model by using only an API. Programming models can also be classified into paradigms based on features of

4214-527: The open source Squeak version of Smalltalk . As part of this effort, in November 1996, his team began research on what became the Etoys system. More recently he started, with David A. Smith , David P. Reed , Andreas Raab , Rick McGeer, Julian Lombardi , and Mark McCahill , the Croquet Project , an open-source networked 2D and 3D environment for collaborative work. In 2001, it became clear that

4312-460: The 1970s, the first version of the Smalltalk programming language was developed at Xerox PARC by Alan Kay , Dan Ingalls and Adele Goldberg . Smalltalk-72 included a programming environment and was dynamically typed , and at first was interpreted , not 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

4410-520: The August issue of Byte Magazine , introducing Smalltalk and object-oriented programming to a wide audience. LOOPS, the object system for Interlisp -D, was influenced by Smalltalk and Flavors, and a paper about it was published in 1982. In 1986, the Association for Computing Machinery organized the first Conference on Object-Oriented Programming, Systems, Languages, and Applications (OOPSLA), which

4508-541: The Children's Machine, and the XO-1 . The program was founded and is sustained by Kay's friend Nicholas Negroponte , and is based on Kay's Dynabook ideal. Kay is a prominent co-developer of the computer, focusing on its educational software using Squeak and Etoys. Kay has lectured extensively on the idea that the computer revolution is very new, and all of the good ideas have not been universally implemented. His lectures at

4606-466: The Davis Group Ltd., Kay said: I had the misfortune or the fortune to learn how to read fluently starting about the age of three, so I had read maybe 150 books by the time I hit first grade, and I already knew the teachers were lying to me. Originally from Springfield, Massachusetts , Kay's family relocated several times due to his father's career in physiology before ultimately settling in

4704-833: The Etoy architecture in Squeak had reached its limits in what the Morphic interface infrastructure could do. Andreas Raab , a researcher in Kay's group then at Hewlett-Packard, proposed defining a "script process" and providing a default scheduling mechanism that avoided several more general problems. The result was a new user interface, proposed to replace the Squeak Morphic user interface. Tweak added mechanisms of islands, asynchronous messaging, players and costumes, language extensions, projects, and tile scripting. Its underlying object system

4802-595: The Fellows program. In 2001, Kay founded Viewpoints Research Institute, a nonprofit organization dedicated to children, learning, and advanced software development. For their first ten years, Kay and his Viewpoints group were based at Applied Minds in Glendale, California , where he and Ferren worked on various projects. Kay served as president of the Institute until its closure in 2018. In 2002 Kay joined HP Labs as

4900-696: The OOP paradigm versus the procedural paradigm. The need for every object to have associative methods leads some skeptics to associate OOP with software bloat ; an attempt to resolve this dilemma came through polymorphism . Although most OOP languages are third-generation, it is possible to create an object-oriented assembler language. High Level Assembly (HLA) is an example of this that fully supports advanced data types and object-oriented assembly language programming – despite its early origins. Thus, differing programming paradigms can be seen rather like motivational memes of their advocates, rather than necessarily representing progress from one level to

4998-560: The OOPSLA 1997 conference, and his ACM Turing Award talk, "The Computer Revolution Hasn't Happened Yet", were informed by his experiences with Sketchpad , Simula , Smalltalk , and the bloated code of commercial software. On August 31, 2006, Kay's proposal to the United States National Science Foundation (NSF) was granted, funding Viewpoints Research Institute for several years. The proposal title

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5096-551: The attribute sugar_content may be defined in apple but not orange . Some languages like Go do not support inheritance at all. Go states that it is object-oriented, and Bjarne Stroustrup, author of C++, has stated that it is possible to do OOP without inheritance. The doctrine of composition over inheritance advocates implementing has-a relationships using composition instead of inheritance. For example, instead of inheriting from class Person, class Employee could give each Employee object an internal Person object, which it then has

5194-484: The class concept covered by "master" or "definition"), albeit specialized to graphical interaction. Also, in 1968, an MIT ALGOL version, AED-0, established a direct link between data structures ("plexes", in that dialect) and procedures, prefiguring what were later termed "messages", "methods", and "member functions". Topics such as data abstraction and modular programming were common points of discussion at this time. Independently of later MIT work such as AED, Simula

5292-432: The class or the instance; this leads to the following terms: Depending on the definition of the language, subclasses may or may not be able to override the methods defined by superclasses. Multiple inheritance is allowed in some languages, though this can make resolving overrides complicated. Some languages have special support for other concepts like traits and mixins , though, in any language with multiple inheritance,

5390-595: The code, and so forth. These can be considered flavors of programming paradigm that apply to only parallel languages and programming models. Some programming language researchers criticise the notion of paradigms as a classification of programming languages, e.g. Harper, and Krishnamurthi. They argue that many programming languages cannot be strictly classified into one paradigm, but rather include features from several paradigms. See Comparison of multi-paradigm programming languages . Different approaches to programming have developed over time. Classification of each approach

5488-410: The data are in the same code unit called an object . This encapsulation ensures that the only way that an object can access data is via methods of the object that contains the data. Thus, an object's inner workings may be changed without affecting code that uses the object. There is controversy raised by Alexander Stepanov , Richard Stallman and other programmers, concerning the efficacy of

5586-737: The development of the influential object-oriented programming language Smalltalk , both personally designing most of the early versions of the language and coining the term "object-oriented." He has been elected a Fellow of the American Academy of Arts and Sciences , the National Academy of Engineering , and the Royal Society of Arts . He received the Turing award in 2003. In an interview on education in America with

5684-418: The discipline imposed by OOP prevents any one programmer from "doing too much damage". Eric S. Raymond , a Unix programmer and open-source software advocate, has been critical of claims that present object-oriented programming as the "One True Solution". Programming paradigm Paradigms are separated along and described by different dimensions of programming. Some paradigms are about implications of

5782-411: The dominant programming paradigm when programming languages supporting the techniques became widely available. These included Visual FoxPro 3.0, C++ , and Delphi . Its dominance was further enhanced by the rising popularity of graphical user interfaces , which rely heavily upon object-oriented programming techniques. An example of a closely related dynamic GUI library and OOP language can be found in

5880-422: The emphasis on abstraction is vital. Object-oriented languages extend the notion of type to incorporate data abstraction, highlighting the significance of restricting access to internal data through methods. Eric S. Raymond has written that object-oriented programming languages tend to encourage thickly layered programs that destroy transparency. Raymond compares this unfavourably to the approach taken with Unix and

5978-588: 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. In the early and mid-1990s object-oriented programming developed as

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6076-403: The execution model. For parallel computing , using a programming model instead of a language is common. The reason is that details of the parallel hardware leak into the abstractions used to program the hardware. This causes the programmer to have to map patterns in the algorithm onto patterns in the execution model (which have been inserted due to leakage of hardware into the abstraction). As

6174-534: The expected result, not as a procedure to follow. Given a database or a set of rules, the computer tries to find a solution matching all the desired properties. An archetype of a declarative language is the fourth generation language SQL , and the family of functional languages and logic programming. Functional programming is a subset of declarative programming. Programs written using this paradigm use functions , blocks of code intended to behave like mathematical functions . Functional languages discourage changes in

6272-440: The extent that the developer knows them. Categorizing the resulting code by paradigm is often an academic activity done in retrospect. Languages categorized as imperative paradigm have two main features: they state the order in which operations occur, with constructs that explicitly control that order, and they allow side effects, in which state can be modified at one point in time, within one unit of code, and then later read at

6370-525: The first language with the primary features of an object-oriented language. It was created for making simulation programs , in which what came to be called objects were the most important information representation. Smalltalk (1972 to 1980) is another early example and the one with which much of the theory of OOP was developed. Concerning the degree of object orientation, the following distinctions can be made: Many widely used languages, such as C++, Java, and Python, provide object-oriented features. Although in

6468-420: The focus from data structures and algorithms to types . Steve Yegge noted that, as opposed to functional programming : Object Oriented Programming puts the nouns first and foremost. Why would you go to such lengths to put one part of speech on a pedestal? Why should one kind of concept take precedence over another? It's not as if OOP has suddenly made verbs less important in the way we actually think. It's

6566-465: The form of either classes or prototypes . These forms of inheritance are significantly different, but analogous terminology is used to define the concepts of object and instance . In class-based programming , the most popular style, each object is required to be an instance of a particular class . The class defines the data format or type (including member variables and their types) and available procedures (class methods or member functions) for

6664-467: The internal workings of an object. This facilitates code refactoring , for example allowing the author of the class to change how objects of that class represent their data internally without changing any external code (as long as "public" method calls work the same way). It 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

6762-485: The invention of a computer language named FLEX . While there, he worked with "fathers of computer graphics " David C. Evans (who had recently been recruited from the University of California, Berkeley to start Utah's computer science department) and Ivan Sutherland (best known for writing such pioneering programs as Sketchpad ). Kay credits Sutherland's 1963 thesis for influencing his views on objects and computer programming . As he grew busier with research for

6860-415: The language grew. 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. During the late 1970s and 1980s, object-oriented programming rose to prominence. The Flavors object-oriented Lisp was developed starting 1979, introducing multiple inheritance and mixins . In 1981, Goldberg edited

6958-430: The languages used to code programs. For perspective, other research studies software engineering processes and describes various methodologies to describe and compare them. A programming language can be described in terms of paradigms. Some languages support only one paradigm. For example, Smalltalk supports object-oriented and Haskell supports functional. Most languages support multiple paradigms. For example,

7056-464: The modern sense of object-oriented programming made its first appearance at the artificial intelligence group at MIT in the late 1950s and early 1960s. "Object" referred to LISP atoms with identified properties (attributes). Another early MIT example was Sketchpad created by Ivan Sutherland in 1960–1961; in the glossary of the 1963 technical report based on his dissertation about Sketchpad, Sutherland defined notions of "object" and "instance" (with

7154-448: The most commercially important recent object-oriented languages are Java , developed by Sun Microsystems , as well as C# and Visual Basic.NET (VB.NET), both designed for Microsoft's .NET platform. Each of these two frameworks shows, in its way, the benefit of using OOP by creating an abstraction from implementation. VB.NET and C# support cross-language inheritance, allowing classes defined in one language to subclass classes defined in

7252-451: The neighborhood of several hundreds of millions of lines of code these days. We wonder: how small could be an understandable practical 'Model T' design that covers this functionality? 1M lines of code? 200K LOC? 100K LOC? 20K LOC?" Kay is a former professional jazz guitarist , composer, and theatrical designer. He also is an amateur classical pipe organist . Kay has received many awards and honors, including: His other honors include

7350-400: The next. Precise comparisons of competing paradigms' efficacy are frequently made more difficult because of new and differing terminology applied to similar entities and processes together with numerous implementation distinctions across languages. A declarative programming program describes what the problem is, not how to solve it. The program is structured as a set of properties to find in

7448-421: The notion of paradigm as used by Thomas Kuhn in his The Structure of Scientific Revolutions (1962). Early programming languages did not have clearly defined programming paradigms and sometimes programs made extensive use of goto statements. Liberal use of which lead to spaghetti code which is difficult to understand and maintain. This led to the development of structured programming paradigms that disallowed

7546-437: The object's behavior in code). Fields may also be known as members, attributes, or properties. Objects are typically stored as contiguous regions of memory . Objects are accessed somewhat like variables with complex internal structures, and in many languages are effectively pointers , serving as actual references to a single instance of said object in memory within a heap or stack. Objects sometimes correspond to things found in

7644-611: The opportunity to hide from external code even if class Person has many public attributes or methods. Delegation is another language feature that can be used as an alternative to inheritance. Rob Pike has criticized the OO mindset for preferring a multilevel type hierarchy with layered abstractions to a three-line lookup table . He has called object-oriented programming "the Roman numerals of computing". Bob Martin states that because they are software, related classes do not necessarily share

7742-448: The order independently. More at Comparison of multi-paradigm programming languages . In object-oriented programming, code is organized into objects that contain state that is owned by and (usually) controlled by the code of the object. Most object-oriented languages are also imperative languages. In object-oriented programming, programs are treated as a set of interacting objects. In functional programming , programs are treated as

7840-473: The other language. Object-oriented programming uses objects, but not all of the associated techniques and structures are supported directly in languages that claim to support OOP. The features listed below are common among languages considered to be strongly class- and object-oriented (or multi-paradigm with OOP support), with notable exceptions mentioned. Christopher J. Date stated that critical comparison of OOP to other technologies, relational in particular,

7938-437: The past object-oriented programming was widely accepted, more recently essays criticizing object-oriented programming and recommending the avoidance of these features (generally in favor of functional programming ) have been very popular in the developer community. Paul Graham has suggested that OOP's popularity within large companies is due to "large (and frequently changing) groups of mediocre programmers". According to Graham,

8036-466: The real world. For example, a graphics program may have objects such as "circle", "square", and "menu". An online shopping system might have objects such as "shopping cart", "customer", and "product". Sometimes objects represent more abstract entities, like an object that represents an open file, or an object that provides the service of translating measurements from U.S. customary to metric. Objects can contain other objects in their instance variables; this

8134-400: The relationships of the things they represent. It is the responsibility of the object, not any external code, to select the procedural code to execute in response to a method call, typically by looking up the method at run time in a table associated with the object. This feature is known as dynamic dispatch . If the call variability relies on more than the single type of the object on which it

8232-446: The same class and its subclasses, but not objects of a different class). In other languages (like Python) this is enforced only by convention (for example, private methods may have names that start with an underscore ). In C#, Swift & Kotlin languages, internal keyword permits access only to files present in the same assembly, package, or module as that of the class. In programming languages, particularly object-oriented ones,

8330-403: The same names. For example, class Person might define variables "first_name" and "last_name" with method "make_full_name()". These will also be available in class Employee, which might add the variables "position" and "salary". It is guaranteed that all instances of class Employee will have the same variables, such as the name, position, and salary. Procedures and variables can be specific to either

8428-409: The step by step process that a computer program follows. The efficacy and efficiency of such a program is therefore highly dependent on the programmer's skill. In attempt to improve on procedural languages, object-oriented programming (OOP) languages were created, such as Simula , Smalltalk , C++ , Eiffel , Python , PHP , Java , and C# . In these languages, data and methods to manipulate

8526-491: The term "object-oriented programming" in conversation as early as 1967. Although sometimes called "the father of object-oriented programming", 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. A 1976 MIT memo co-authored by Barbara Liskov lists Simula 67 , CLU , and Alphard as object-oriented languages, but does not mention Smalltalk. In

8624-510: The use of goto statements; only allowing the use of more structured programming constructs. Machine code is the lowest-level of computer programming as it is machine instructions that define behavior at the lowest level of abstract possible for a computer. As it is the most prescriptive way to code it is classified as imperative. It is sometimes called the first-generation programming language . Assembly language introduced mnemonics for machine instructions and memory addresses . Assembly

8722-489: The use of logical operators such as READ/WRITE/GET/PUT. Assembly was, and still is, used for time-critical systems and often in embedded systems as it gives the most control of what the machine does. Procedural languages , also called the third-generation programming languages are the first described as high-level languages . They support vocabulary related to the problem being solved. For example, These languages are classified as procedural paradigm. They directly control

8820-541: The use of the words 'object' and 'class', had been developed for Simula 67 at the Norwegian Computing Center . Kay said: I'm sorry that I long ago coined the term "objects" for this topic because it gets many people to focus on the lesser idea. The big idea is " messaging ". While at PARC, Kay conceived the Dynabook concept, a key progenitor of laptop and tablet computers and the e-book . He

8918-443: The value of variables through assignment , making a great deal of use of recursion instead. The logic programming paradigm views computation as automated reasoning over a body of knowledge. Facts about the problem domain are expressed as logic formulas, and programs are executed by applying inference rules over them until an answer to the problem is found, or the set of formulas is proved inconsistent. Symbolic programming

9016-480: The world in terms of interfaces that vary on a single type. To deal with the real problems you need multisorted algebras — families of interfaces that span multiple types. I find OOP philosophically unsound. It claims that everything is an object. Even if it is true it is not very interesting — saying that everything is an object is saying nothing at all. OOP languages are diverse, but typically OOP languages allow inheritance for code reuse and extensibility in

9114-482: Was "STEPS Toward the Reinvention of Programming: A compact and Practical Model of Personal Computing as a Self-exploratorium". STEPS is a recursive acronym that stands for "STEPS Toward Expressive Programming Systems". A sense of what Kay is trying to do comes from this quote, from the abstract of a seminar at Intel Research Labs, Berkeley: "The conglomeration of commercial and most open source software consumes in

9212-567: Was Chief Scientist at Atari . In 1984, he became an Apple Fellow. After the closure of the Apple Advanced Technology Group in 1997, he was recruited by his friend Bran Ferren , head of research and development at Disney , to join Walt Disney Imagineering as a Disney Fellow. He remained there until Ferren left to start Applied Minds Inc with Imagineer Danny Hillis , leading to the cessation of

9310-543: Was attended by 1,000 people. Among other developments was 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

9408-503: Was developed during the years 1961–1967. Simula introduced important concepts that are today an essential part of object-oriented programming, such as class and object , inheritance, and dynamic binding . The object-oriented Simula programming language was used mainly by researchers involved with physical modelling , such as models to study and improve the movement of ships and their content through cargo ports. I thought of objects being like biological cells and/or individual computers on

9506-466: Was either described at the time the approach was first developed, but often not until some time later, retrospectively. An early approach consciously identified as such is structured programming , advocated since the mid 1960s. The concept of a programming paradigm as such dates at least to 1978, in the Turing Award lecture of Robert W. Floyd , entitled The Paradigms of Programming , which cites

9604-636: Was present in San Francisco for the Mother of all Demos , a landmark computer demonstration by Douglas Engelbart . Even though he was sick with a high fever on that day, the event was very influential in Kay's career. He recalled later: "It was one of the greatest experiences in my life". In 1969, Kay became a visiting researcher at the Stanford Artificial Intelligence Laboratory in anticipation of accepting

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