In
object-oriented programming
Object-oriented programming (OOP) is a programming paradigm based on the concept of '' objects''. Objects can contain data (called fields, attributes or properties) and have actions they can perform (called procedures or methods and impl ...
, an interface or protocol type is a
data type
In computer science and computer programming, a data type (or simply type) is a collection or grouping of data values, usually specified by a set of possible values, a set of allowed operations on these values, and/or a representation of these ...
that acts as an
abstraction
Abstraction is a process where general rules and concepts are derived from the use and classifying of specific examples, literal (reality, real or Abstract and concrete, concrete) signifiers, first principles, or other methods.
"An abstraction" ...
of a
class
Class, Classes, 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 d ...
. It describes a set of
method signature
In computer science, a type signature or type annotation defines the inputs and outputs of a function, subroutine or method. A type signature includes the number, types, and order of the function's arguments. One important use of a type signat ...
s, the implementations of which may be provided by multiple
class
Class, Classes, 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 d ...
es that are otherwise not necessarily related to each other.
A class which provides the methods listed in an interface is said to ''implement'' the interface,
or to ''adopt'' the protocol.
Examples
If objects are fully
encapsulated then the interface is the only way in which they may be accessed by other objects. For example, in
Java
Java is one of the Greater Sunda Islands in Indonesia. It is bordered by the Indian Ocean to the south and the Java Sea (a part of Pacific Ocean) to the north. With a population of 156.9 million people (including Madura) in mid 2024, proje ...
, 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.
Programming languages are described in terms of their Syntax (programming languages), syntax (form) and semantics (computer science), semantics (meaning), usually def ...
s provide explicit language support for interfaces:
Ada,
C#,
D,
Dart,
Delphi
Delphi (; ), in legend previously called Pytho (Πυθώ), was an ancient sacred precinct and the seat of Pythia, the major oracle who was consulted about important decisions throughout the ancient Classical antiquity, classical world. The A ...
,
Go,
Java
Java is one of the Greater Sunda Islands in Indonesia. It is bordered by the Indian Ocean to the south and the Java Sea (a part of Pacific Ocean) to the north. With a population of 156.9 million people (including Madura) in mid 2024, proje ...
,
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.
T ...
,
Objective-C
Objective-C is a high-level general-purpose, object-oriented programming language that adds Smalltalk-style message passing (messaging) to the C programming language. Originally developed by Brad Cox and Tom Love in the early 1980s, it was ...
,
OCaml
OCaml ( , formerly Objective Caml) is a General-purpose programming language, general-purpose, High-level programming language, high-level, Comparison of multi-paradigm programming languages, multi-paradigm programming language which extends the ...
,
PHP
PHP is a general-purpose scripting language geared towards 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 Languag ...
,
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
* SWIF ...
,
Python 3.8. 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 ...
, such as
C++, interfaces are implemented as
abstract class
In object-oriented programming, a class defines the shared aspects of objects created from the class. The capabilities of a class differ between programming languages, but generally the shared aspects consist of state ( variables) and behavior ( ...
es.
In languages without explicit support, interfaces are often still present as conventions; this is known as
duck typing
In computer programming, duck typing 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 ...
. For example, in
Python, any class can implement an
__iter__ method and be used as a
collection.
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 a ...
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 pioneered several programming language ...
, or module signatures in
ML and
OCaml
OCaml ( , formerly Objective Caml) is a General-purpose programming language, general-purpose, High-level programming language, high-level, Comparison of multi-paradigm programming languages, multi-paradigm programming language which extends the ...
, are used for many of the things that interfaces are used for.
In
Rust
Rust is an iron oxide, a usually reddish-brown oxide formed by the reaction of iron and oxygen in the catalytic presence of water or air moisture. Rust consists of hydrous iron(III) oxides (Fe2O3·nH2O) and iron(III) oxide-hydroxide (FeO(OH) ...
, interfaces are called ''trait''s.
See also
*
Concept (generic programming) In generic programming, a concept is a description of supported operations on a type, including syntax and semantics. In this way, concepts are related to abstract types but concepts do not require a subtype relationship.
Language use
The term w ...
*
Delegation (programming)
In computing or computer programming, delegation refers generally to one entity passing something to another entity,Barry Wilkinson, ''Grid Computing: Techniques and Applications'' (2009), p. 164, . and narrowly to various specific forms of relat ...
*
Protocols in Objective-C
*
Class (computer science)
In object-oriented programming, a class defines the shared aspects of objects created from the class. The capabilities of a class differ between programming languages, but generally the shared aspects consist of state ( variables) and behavior ( ...
*
Encapsulation (computer science)
Encapsulation may refer to:
Chemistry
* Molecular encapsulation, in chemistry, the confinement of an individual molecule within a larger molecule
* Micro-encapsulation, in material science, the coating of microscopic particles with another mat ...
*
Public interface
*
Interface (Java)
An interface in the Java programming language is an abstract type that is used to declare a behavior that classes must implement. They are similar to protocols. Interfaces are declared using the interface keyword, and may only contain method si ...
*
Application programming interface
An application programming interface (API) is a connection between computers or between computer programs. It is a type of software Interface (computing), interface, offering a service to other pieces of software. A document or standard that des ...
*
Interface (computing)
In computing, an interface (American English) or interphase (British English, archaic) is a shared boundary across which two or more separate components of a computer system exchange information. The exchange can be between software, computer hard ...
*
List of basic computer science topics
Notes
References
{{DEFAULTSORT:Protocol (Object-priented programming)
Object-oriented programming
Data types