object-oriented programming Object-oriented programming (OOP) is a programming paradigm based on the concept of "objects", which can contain data and code. The data is in the form of fields (often known as attributes or ''properties''), and the code is in the form of pr ...

, an interface or protocol type is a

data type In computer science and computer programming, a data type (or simply type) is a set of possible values and a set of allowed operations on it. A data type tells the compiler or interpreter how the programmer intends to use the data. Most progra ...

describing a set of method signatures, the implementations of which may be provided by multiple

class Class or The Class may refer to: Common uses not otherwise categorized * Class (biology), a taxonomic rank * Class (knowledge representation), a collection of individuals or objects * Class (philosophy), an analytical concept used differentl ...

es that are otherwise not necessarily related to each other. A class which provides the methods listed in a protocol is said to ''adopt'' the protocol, or to ''implement'' the interface. If objects are fully encapsulated then the protocol is the only way in which they may be accessed by other objects. For example, in

Java Java (; id, Jawa, ; jv, ꦗꦮ; su, ) is one of the Greater Sunda Islands in Indonesia. It is bordered by the Indian Ocean to the south and the Java Sea to the north. With a population of 151.6 million people, Java is the world's List ...

, the Comparable interface specifies a method compareTo() which implementing classes must implement. This means that a sorting method, for example, can sort a collection of any objects of types which implement the Comparable interface, without having to know anything about the inner nature of the class (except that two of these objects can be compared by means of compareTo()). Some

programming language A programming language is a system of notation for writing computer programs. Most programming languages are text-based formal languages, but they may also be graphical. They are a kind of computer language. The description of a programming ...

s provide explicit language support for protocols (

Ada Ada may refer to: Places Africa * Ada Foah, a town in Ghana * Ada (Ghana parliament constituency) * Ada, Osun, a town in Nigeria Asia * Ada, Urmia, a village in West Azerbaijan Province, Iran * Ada, Karaman, a village in Karaman Province, ...

, C#, D,

Dart Dart or DART may refer to: * Dart, the equipment in the game of darts Arts, entertainment and media * Dart (comics), an Image Comics superhero * Dart, a character from ''G.I. Joe'' * Dart, a ''Thomas & Friends'' railway engine character * Dar ...

Delphi Delphi (; ), in legend previously called Pytho (Πυθώ), in ancient times was a sacred precinct that served as the seat of Pythia, the major oracle who was consulted about important decisions throughout the ancient classical world. The oracle ...

, Go,

Logtalk Logtalk is an object-oriented logic programming language that extends and leverages the Prolog language with a feature set suitable for programming in the large.Paulo Moura (2003). Logtalk: Design of an Object-Oriented Logic Programming Language. ...

Object Pascal Object Pascal is an extension to the programming language Pascal (programming language), Pascal that provides object-oriented programming (OOP) features such as Class (computer programming), classes and Method (computer programming), methods. ...

Objective-C Objective-C is a general-purpose, object-oriented programming language that adds Smalltalk-style messaging to the C programming language. Originally developed by Brad Cox and Tom Love in the early 1980s, it was selected by NeXT for its NeXTS ...

OCaml OCaml ( , formerly Objective Caml) is a general-purpose programming language, general-purpose, multi-paradigm programming language which extends the Caml dialect of ML (programming language), ML with object-oriented programming, object-oriented ...

PHP PHP is a general-purpose scripting language geared toward web development. It was originally created by Danish-Canadian programmer Rasmus Lerdorf in 1993 and released in 1995. The PHP reference implementation is now produced by The PHP Group ...

, Racket,

Seed7 Seed7 is an extensible general-purpose programming language designed by Thomas Mertes. It is syntactically similar to Pascal and Ada. Along with many other features, it provides an extension mechanism. Daniel Zingaro"Modern Extensible Languages" ...

Swift Swift or SWIFT most commonly refers to: * SWIFT, an international organization facilitating transactions between banks ** SWIFT code * Swift (programming language) * Swift (bird), a family of birds It may also refer to: Organizations * SWIFT, ...

). In languages supporting

multiple inheritance Multiple inheritance is a feature of some object-oriented computer programming languages in which an object or class can inherit features from more than one parent object or parent class. It is distinct from single inheritance, where an object or ...

, such as

C++ C++ (pronounced "C plus plus") is a high-level general-purpose programming language created by Danish computer scientist Bjarne Stroustrup as an extension of the C programming language, or "C with Classes". The language has expanded significan ...

, interfaces are implemented as

abstract class In programming languages, an abstract type is a type in a nominative type system that cannot be instantiated directly; a type that is not abstract – which ''can'' be instantiated – is called a ''concrete type''. Every instance of an abstra ...

es. In languages without explicit support, protocols are often still present as conventions. This is known as

duck typing Duck typing in computer programming is an application of the duck test—"If it walks like a duck and it quacks like a duck, then it must be a duck"—to determine whether an object can be used for a particular purpose. With nominative t ...

. For example, in

Python Python may refer to: Snakes * Pythonidae, a family of nonvenomous snakes found in Africa, Asia, and Australia ** ''Python'' (genus), a genus of Pythonidae found in Africa and Asia * Python (mythology), a mythical serpent Computing * Python (pro ...

, any class can implement an __iter__ method and be used as a

collection Collection or Collections may refer to: * Cash collection, the function of an accounts receivable department * Collection (church), money donated by the congregation during a church service * Collection agency, agency to collect cash * Collectio ...

Type class In computer science, a type class is a type system construct that supports ad hoc polymorphism. This is achieved by adding constraints to type variables in parametrically polymorphic types. Such a constraint typically involves a type class T and ...

es in languages like

Haskell Haskell () is a general-purpose, statically-typed, purely functional programming language with type inference and lazy evaluation. Designed for teaching, research and industrial applications, Haskell has pioneered a number of programming lan ...

, or module signatures in ML and

, are used for many of the things that protocols are used for.

Notes

References

{{compu-prog-stub Object-oriented programming

See also

Notes

References