In computer science , control flow (or flow of control ) is the order in which individual statements , instructions or function calls of an imperative program are executed or evaluated. The emphasis on explicit control flow distinguishes an imperative programming language from a declarative programming language.
109-451: ActionScript is an object-oriented programming language originally developed by Macromedia Inc. (later acquired by Adobe ). It is influenced by HyperTalk , the scripting language for HyperCard . It is now an implementation of ECMAScript (meaning it is a superset of the syntax and semantics of the language more widely known as JavaScript ), though it originally arose as a sibling, both being influenced by HyperTalk . ActionScript code
218-532: A server ) should loop forever, handling events as they occur, only stopping when the process is terminated by an operator. Infinite loops can be implemented using other control flow constructs. Most commonly, in unstructured programming this is jump back up (goto), while in structured programming this is an indefinite loop (while loop) set to never end, either by omitting the condition or explicitly setting it to true, as while (true) ... . Some languages have special constructs for infinite loops, typically by omitting
327-402: A desire to skip the remainder of the loop body and continue with the next iteration of the loop. Some languages provide a statement such as continue (most languages), skip , cycle (Fortran), or next (Perl and Ruby), which will do this. The effect is to prematurely terminate the innermost loop body and then resume as normal with the next iteration. If the iteration is the last one in
436-744: A different set of APIs for creating objects. Compare the script below to the previous ActionScript 2.0 version: Minimal ActionScript 3.0 programs may be somewhat larger and more complicated due to the increased separation of the programming language and the Flash integrated development environment (IDE). Presume the following file to be Greeter.as : ActionScript 3 can also be used in MXML files when using Apache's Flex framework: ActionScript primarily consists of "fundamental" or "simple" data types that are used to create other data types. These data types are very similar to Java data types. Since ActionScript 3
545-786: 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
654-431: A final keyword. Conditional expressions and conditional constructs are features of a programming language that perform different computations or actions depending on whether a programmer-specified Boolean condition evaluates to true or false. Less common variations include: Switch statements (or case statements , or multiway branches ) compare a given value with specified constants and take action according to
763-430: 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
872-482: 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,
981-402: 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
1090-450: A human. Less robust obfuscators insert traps for decompilers. Such obfuscators either cause the decompiler software to crash unexpectedly or to generate unintelligible source code. Object-oriented programming 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
1199-485: 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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#17327727503881308-509: A multilevel break or continue – this was proposed in PEP 3136 , and rejected on the basis that the added complexity was not worth the rare legitimate use. The notion of multi-level breaks is of some interest in theoretical computer science , because it gives rise to what is today called the Kosaraju hierarchy . In 1973 S. Rao Kosaraju refined the structured program theorem by proving that it
1417-580: 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
1526-457: 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
1635-457: A set or collection. Scala has for-expressions , which generalise collection-controlled loops, and also support other uses, such as asynchronous programming . Haskell has do-expressions and comprehensions, which together provide similar function to for-expressions in Scala. General iteration constructs such as C's for statement and Common Lisp 's do form can be used to express any of
1744-421: 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
1853-591: A specific type by adding a type annotation so that type mismatch errors could be found at compile-time . ActionScript 2.0 also introduced class-based inheritance syntax so that developers could create classes and interfaces, much as they would in class-based languages such as Java and C++ . This version conformed partially to the ECMAScript Fourth Edition draft specification. In June 2006, ActionScript 3.0 debuted with Adobe Flex 2.0 and its corresponding player, Flash Player 9 . ActionScript 3.0
1962-401: A state variable which is tested to break out another level; exceptions, which are caught at the level being broken out to; placing the nested loops in a function and using return to effect termination of the entire nested loop; or using a label and a goto statement. C does not include a multilevel break, and the usual alternative is to use a goto to implement a labeled break. Python does not have
2071-493: A statement without disrupting the control flow. In other words, they were composable . (Later developments, such as non-strict programming languages – and more recently, composable software transactions – have continued this strategy, making components of programs even more freely composable.) Some academics took a purist approach to the Böhm–Jacopini result and argued that even instructions like break and return from
2180-437: 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
2289-433: A text field at depth 0, at position (0, 0) on the screen (measured in pixels ), that is 100 pixels wide and high. Then the text parameter is set to the " Hello, world " string , and it is automatically displayed in the player: When writing external ActionScript 2.0 class files the above example could be written in a file named Greeter.as as following. ActionScript 3.0 has a similar syntax to ActionScript 2.0, but
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#17327727503882398-448: 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
2507-493: 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
2616-403: 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
2725-412: Is an explicit name or number assigned to a fixed position within the source code , and which may be referenced by control flow statements appearing elsewhere in the source code. A label marks a position within source code and has no other effect. Line numbers are an alternative to a named label used in some languages (such as BASIC ). They are whole numbers placed at the start of each line of text in
2834-676: Is at the start, the body may be skipped completely; if it is at the end, the body is always executed at least once. A control break is a value change detection method used within ordinary loops to trigger processing for groups of values. Values are monitored within the loop and a change diverts program flow to the handling of the group event associated with them. Several programming languages (e.g., Ada , D , C++11 , Smalltalk , PHP , Perl , Object Pascal , Java , C# , MATLAB , Visual Basic , Ruby , Python , JavaScript , Fortran 95 and later) have special constructs which allow implicit looping through all elements of an array, or all members of
2943-405: 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
3052-516: 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
3161-520: 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
3270-429: 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
3379-477: Is found. Some programming languages provide a statement such as break (most languages), Exit (Visual Basic), or last (Perl), which effect is to terminate the current loop immediately, and transfer control to the statement immediately after that loop. Another term for early-exit loops is loop-and-a-half . The following example is done in Ada which supports both early exit from loops and loops with test in
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3488-564: 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
3597-553: Is met, or indefinitely . When one of those items is itself also a loop, it is called a "nested loop". In functional programming languages, such as Haskell and Scheme , both recursive and iterative processes are expressed with tail recursive procedures instead of looping constructs that are syntactic. Most programming languages have constructions for repeating a loop a certain number of times. In most cases counting can go downwards instead of upwards and step sizes other than 1 can be used. In these examples, if N < 1 then
3706-408: 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
3815-682: Is offered free of charge and both an open-source compiler (as part of Apache Flex ) and open-source virtual machine ( Tamarin ) are available. ActionScript was also used with Scaleform GFx for the development of three-dimensional video-game user interfaces and heads up displays . ActionScript was initially designed for controlling simple two-dimensional vector animations made in Adobe Flash (formerly Macromedia Flash). Initially focused on animation, early versions of Flash content offered few interactivity features, thus had very limited scripting ability. Later versions added functionality allowing for
3924-537: Is often possible by scripting something rather than animating it, which usually also enables a higher level of flexibility when editing. Since the arrival of the Flash Player 9 alpha (in 2006), a newer version of ActionScript has been released, ActionScript 3.0. This version of the language is intended to be compiled and run on a version of the Tamarin virtual machine, formerly ActionScript Virtual Machine 2, that
4033-460: Is particularly well-suited for small-scale scripting projects. Prototype-based inheritance is the ActionScript 1.0 mechanism for code reuse and object-oriented programming. Instead of a class keyword that defines common characteristics of a class , ActionScript 1.0 uses a special object that serves as a "prototype" for a class of objects. All common characteristics of a class are defined in
4142-466: Is possible to avoid adding additional variables in structured programming, as long as arbitrary-depth, multi-level breaks from loops are allowed. Furthermore, Kosaraju proved that a strict hierarchy of programs exists: for every integer n , there exists a program containing a multi-level break of depth n that cannot be rewritten as a program with multi-level breaks of depth less than n without introducing added variables. One can also return out of
4251-450: 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 –
4360-541: Is usually converted to bytecode format by a compiler . ActionScript is used primarily for the development of websites and software targeting the Adobe Flash platform, originally finding use on web pages in the form of embedded SWF files. ActionScript 3 is also used with the Adobe AIR system for the development of desktop and mobile applications. The language itself is open-source in that its specification
4469-635: 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
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4578-463: The var statement, and user-defined functions with parameter passing and return values can also be created. Notably, ActionScript could now also be typed with a text editor rather than being assembled by choosing actions from drop-down lists and dialog box controls. With the next release of its authoring tool, Flash MX, and its corresponding player, Flash Player 6 , the language remained essentially unchanged; there were only minor changes, such as
4687-427: 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
4796-583: 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
4905-541: 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
5014-580: The keyword may either be in upper or lower case depending on the language, it is usually written as: The effect of a goto statement is to cause the next statement to be executed to be the statement appearing at (or immediately after) the indicated label. Goto statements have been considered harmful by many computer scientists, notably Dijkstra . The terminology for subroutines varies; they may alternatively be known as routines, procedures, functions (especially if they return results) or methods (especially if they belong to classes or type classes ). In
5123-602: The "delete" keyword. Removal of actual objects and data is done by the Flash Player garbage collector which checks for any existing references in the Flash memory space. If none are found (no other reference is made to the orphaned object), it is removed from memory. For this reason, memory management in ActionScript requires careful application development planning. Like most bytecode file formats, Flash SWF files can be decompiled into their source code and assets (similarly to how Microsoft .NET files can be decompiled). Some decompilers are capable of nearly full reconstruction of
5232-479: The 1950s, computer memories were very small by current standards so subroutines were used mainly to reduce program size. A piece of code was written once and then used many times from various other places in a program. Today, subroutines are more often used to help make a program more structured, e.g., by isolating some algorithm or hiding some data access method. If many programmers are working on one program, subroutines are one kind of modularity that can help divide
5341-460: 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
5450-522: 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
5559-612: The Flash 4 user manual and marketing documents continued to use the term "actions" to describe this set of commands. With the release of Flash 5 in September 2000, the "actions" from Flash 4 were enhanced once more and named "ActionScript" for the first time. This was the first version of ActionScript with influences from JavaScript and the ECMA-262 (Third Edition) standard, supporting the said standard's object model and many of its core data types . Local variables may be declared with
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#17327727503885668-552: The Flash authoring tool provided limited interactivity features. Early Flash developers could attach a simple command, called an "action", to a button or a frame. The set of actions was basic navigation controls, with commands such as "play", "stop", "getURL", and "gotoAndPlay". With the release of Flash 4 in 1999, this simple set of actions became a small scripting language. New capabilities introduced for Flash 4 included variables , expressions , operators , if statements , and loops . Although referred to internally as "ActionScript",
5777-477: The Pascal-provided control structures, the correct solution was given by only 20% of the subjects, while no subject wrote incorrect code for this problem if allowed to write a return from the middle of a loop. Most programming languages with control structures have an initial keyword which indicates the type of control structure involved. Languages then divide as to whether or not control structures have
5886-454: The Stage3D engine Adobe has developed. The number of APIs (Application programming interfaces) available to ActionScript 3.0 has also risen dramatically. ActionScript code is free form and thus may be created with whichever amount or style of whitespace that the author desires. The basic syntax is derived from ECMAScript . The following code, which works in any compliant player, creates
5995-704: The above example is linked to the for statement, and not the inner if statement. Both Python's for and while loops support such an else clause, which is executed only if early exit of the loop has not occurred. Some languages support breaking out of nested loops; in theory circles, these are called multi-level breaks. One common use example is searching a multi-dimensional table. This can be done either via multilevel breaks (break out of N levels), as in bash and PHP, or via labeled breaks (break out and continue at given label), as in Go, Java and Perl. Alternatives to multilevel breaks include single breaks, together with
6104-450: The above sorts of loops, and others, such as looping over some number of collections in parallel. Where a more specific looping construct can be used, it is usually preferred over the general iteration construct, since it often makes the purpose of the expression clearer. Infinite loops are used to assure a program segment loops forever or until an exceptional condition arises, such as an error. For instance, an event-driven program (such as
6213-614: The addition of Boolean variables (true/false flags). Later authors showed that choice can be replaced by loops (and yet more Boolean variables). That such minimalism is possible does not mean that it is necessarily desirable; computers theoretically need only one machine instruction (subtract one number from another and branch if the result is negative), but practical computers have dozens or even hundreds of machine instructions. Other research showed that control structures with one entry and one exit were much easier to understand than any other form, mainly because they could be used anywhere as
6322-419: The addition of the switch statement and the "strict equality" ( === ) operator, which brought it closer to being ECMA-262 -compliant. Two important features of ActionScript that distinguish it from later versions are its loose type system and its reliance on prototype-based inheritance . Loose typing refers to the ability of a variable to hold any type of data. This allows for rapid script development and
6431-553: 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
6540-436: The body of loop may execute once (with I having value 1) or not at all, depending on the programming language. In many programming languages, only integers can be reliably used in a count-controlled loop. Floating-point numbers are represented imprecisely due to hardware constraints, so a loop such as might be repeated 9 or 10 times, depending on rounding errors and/or the hardware and/or the compiler version. Furthermore, if
6649-577: The browser. This technology is known as Asynchronous Flash and XML, much like AJAX. Adobe offers its Flex product line to meet the demand for rich web applications built on the Flash runtime, with behaviors and programming done in ActionScript. ActionScript 3.0 forms the foundation of the Flex 2 application programming interface ( API ). ActionScript started as an object-oriented programming language for Macromedia 's Flash authoring tool, later developed by Adobe Systems as Adobe Flash. The first three versions of
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#17327727503886758-487: 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
6867-432: 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,
6976-470: The class's prototype object and every instance of that class contains a link to that prototype object. The next major revision of the language, ActionScript 2.0, was introduced in September 2003 with the release of Flash MX 2004 and its corresponding player, Flash Player 7 . In response to user demand for a language better equipped for larger and more complex applications, ActionScript 2.0 featured compile-time type checking and class-based syntax , such as
7085-400: The condition from an indefinite loop. Examples include Ada ( loop ... end loop ), Fortran ( DO ... END DO ), Go ( for { ... } ), and Ruby ( loop do ... end ). Often, an infinite loop is unintentionally created by a programming error in a condition-controlled loop, wherein the loop condition uses variables that never change within the loop. Sometimes within the body of a loop there is
7194-489: The creation of web-based games and rich web applications with streaming media (such as video and audio). Today, ActionScript is suitable for desktop and mobile development through Adobe AIR; it is used in some database applications and in basic robotics as in Make Controller Kit . Flash MX 2004 introduced ActionScript 2.0, a scripting language more suited to the development of Flash applications. Saving time
7303-487: The default case as a glob matching any string. Case logic can also be implemented in functional form, as in SQL 's decode statement. A loop is a sequence of statements which is specified once but which may be carried out several times in succession. The code "inside" the loop (the body of the loop, shown below as xxx ) is obeyed a specified number of times, or once for each of a collection of items, or until some condition
7412-546: 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". Program loops Within an imperative programming language , a control flow statement is a statement that results in a choice being made as to which of two or more paths to follow. For non-strict functional languages, functions and language constructs exist to achieve
7521-415: 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
7630-424: 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
7739-589: 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
7848-404: The first constant to match. There is usually a provision for a default action ("else", "otherwise") to be taken if no match succeeds. Switch statements can allow compiler optimizations, such as lookup tables . In dynamic languages , the cases may not be limited to constant expressions, and might extend to pattern matching , as in the shell script example on the right, where the *) implements
7957-525: 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
8066-422: 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
8175-454: The following statement), but few if any other ALGOL variants allowed whole numbers. Early Fortran compilers only allowed whole numbers as labels. Beginning with Fortran-90, alphanumeric labels have also been allowed. The goto statement (a combination of the English words go and to , and pronounced accordingly) is the most basic form of unconditional transfer of control. Although
8284-843: 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 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
8393-465: 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
8502-568: The function will alter the original variable as well, as no new XML Object is created. Some data types can be assigned values with literals : A reference in ActionScript is a pointer to an instance of a class. A reference stores the memory address of an object – operations against references will follow the value of the reference to the memory address of the object and carry out the operation on that object. All objects in ActionScript are accessed through references instead of being accessed directly. Only references to an object may be removed by using
8611-404: The increment of X occurs by repeated addition, accumulated rounding errors may mean that the value of X in each iteration can differ quite significantly from the expected sequence 0.1, 0.2, 0.3, ..., 1.0. Most programming languages have constructions for repeating a loop until some condition changes. Some variations test the condition at the start of the loop; others test it at the end. If the test
8720-467: 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
8829-424: The keywords class and extends . While this allowed for a more structured object-oriented programming approach, the code would still be compiled to ActionScript 1.0 bytecode , allowing it to be used on the preceding Flash Player 6 as well. In other words, the class-based inheritance syntax was a layer on top of the existing prototype-based system. With ActionScript 2.0, developers could constrain variables to
8938-418: 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
9047-422: The level of machine language or assembly language , control flow instructions usually work by altering the program counter . For some central processing units (CPUs), the only control flow instructions available are conditional or unconditional branch instructions, also termed jumps. The kinds of control flow statements supported by different languages vary, but can be categorized by their effect: A label
9156-402: The loop, the effect is to terminate the entire loop early. Some languages, like Perl and Ruby, have a redo statement that restarts the current iteration from the start. Ruby has a retry statement that restarts the entire loop from the initial iteration. When using a count-controlled loop to search through a table, it might be desirable to stop searching as soon as the required item
9265-429: The middle . Both features are very similar and comparing both code snippets will show the difference: early exit must be combined with an if statement while a condition in the middle is a self-contained construct. Python supports conditional execution of code depending on whether a loop was exited early (with a break statement) or not by using an else-clause with the loop. For example, The else clause in
9374-456: The middle of loops are bad practice as they are not needed in the Böhm–Jacopini proof, and thus they advocated that all loops should have a single exit point. This purist approach is embodied in the language Pascal (designed in 1968–1969), which up to the mid-1990s was the preferred tool for teaching introductory programming in academia. The direct application of the Böhm–Jacopini theorem may result in additional local variables being introduced in
9483-466: 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
9592-448: 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
9701-437: 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
9810-613: 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
9919-588: The original source file, down to the actual code that was used during creation (although results vary on a case-by-case basis). In opposition to the decompilers, ActionScript obfuscators have been introduced, which transform code into a form that breaks decompiler output while preserving the functionality and structure of the program. Higher-quality obfuscators implement lexical transformations such as identifier renaming, control flow transformation, and data abstraction transformation which collectively make it harder for decompilers to generate output likely to be useful to
10028-477: 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,
10137-439: 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,
10246-440: The primitive data types, which includes Boolean, Number, int, uint, and String, are immutable. So if a variable of a supposedly primitive type, e.g. an integer is passed to a function, altering that variable inside the function will not alter the original variable, as a new int Object is created when inside the function. If a variable of another (not primitive) datatype, e.g. XML is passed to a function, altering that variable inside
10355-467: 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
10464-401: 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
10573-448: 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,
10682-403: 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
10791-498: The same result, but they are usually not termed control flow statements. A set of statements is in turn generally structured as a block , which in addition to grouping, also defines a lexical scope . Interrupts and signals are low-level mechanisms that can alter the flow of control in a way similar to a subroutine , but usually occur as a response to some external stimulus or event (that can occur asynchronously ), rather than execution of an in-line control flow statement. At
10900-592: The source code. Languages which use these often impose the constraint that the line numbers must increase in value in each following line, but may not require that they be consecutive. For example, in BASIC: In other languages such as C and Ada , a label is an identifier , usually appearing at the start of a line and immediately followed by a colon. For example, in C: The language ALGOL 60 allowed both whole numbers and identifiers as labels (both linked by colons to
11009-471: The structured chart, and may also result in some code duplication . Pascal is affected by both of these problems and according to empirical studies cited by Eric S. Roberts , student programmers had difficulty formulating correct solutions in Pascal for several simple problems, including writing a function for searching an element in an array. A 1980 study by Henry Shapiro cited by Roberts found that using only
11118-495: 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
11227-619: The work. In structured programming, the ordered sequencing of successive commands is considered one of the basic control structures, which is used as a building block for programs alongside iteration, recursion and choice. In May 1966, Böhm and Jacopini published an article in Communications of the ACM which showed that any program with goto s could be transformed into a goto-free form involving only choice (IF THEN ELSE) and loops (WHILE condition DO xxx), possibly with duplicated code and/or
11336-480: 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
11445-774: Was a complete rewrite of ActionScript 2, the data types and their inheritances have changed. ActionScript 2 top level data types ActionScript 2 complex data types There are additional "complex" data types. These are more processor and memory intensive and consist of many "simple" data types. For AS2, some of these data types are: ActionScript 3 primitive (prime) data types ActionScript 3 some complex data types The basic syntax is: So in order to make an empty Object: Or, in an informal way: Some types are automatically put in place: Unlike some object-oriented languages, ActionScript makes no distinction between primitive types and reference types. In ActionScript, all variables are reference types. However, objects that belong to
11554-496: Was a fundamental restructuring of the language, so much so that it uses an entirely different virtual machine . Flash Player 9 contains two virtual machines, AVM1 for code written in ActionScript 1.0 and 2.0, and AVM2 for content written in ActionScript 3.0. ActionScript 3.0 added limited support for hardware acceleration ( DirectX , OpenGL ). The update to the language introduced several new features: Adobe AIR supports ActionScript, in addition to some extended contents, such as
11663-469: Was also fully rewritten (dubbed AVM2). Because of this, code written in ActionScript 3.0 is generally targeted for Flash Player 9 and higher, and will not work in prior versions. At the same time, ActionScript 3.0 executes up to 10 times faster than legacy ActionScript code due to the just-in-time compiler enhancements. Flash libraries can be used with the XML abilities of the browser to render rich content in
11772-543: 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
11881-506: 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
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