Interface (object-oriented programming)

Inobject-oriented programming,aninterfaceorprotocoltypeis adata typethat acts as anabstractionof aclass.It describes a set ofmethod signatures,the implementations of which may be provided by multipleclassesthat are otherwise not necessarily related to each other.A class which provides the methods listed in a protocol is said toadoptthe protocol,or toimplementthe interface.

If objects are fullyencapsulatedthen the protocol is the only way in which they may be accessed by other objects. For example, inJava,theComparableinterface specifies a methodcompareTo()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 ofcompareTo()).

Someprogramming languagesprovide explicit language support for protocols (Ada,C#,D,Dart,Delphi,Go,Java,Logtalk,Object Pascal,Objective-C,OCaml,PHP,Racket,Seed7,Swift,Python3.8). In languages supportingmultiple inheritance,such asC++,interfaces are implemented asabstract classes.

In languages without explicit support, protocols are often still present as conventions. This is known asduck typing.For example, inPython,any class can implement an__iter__method and be used as acollection.

Type classesin languages likeHaskell,or module signatures inMLandOCaml,are used for many of the things that protocols are used for.

InRust,interfaces are calledtraits.

See also

• Concept (generic programming)
• Delegation (programming)
• Protocols in Objective-C
• Class (computer science)
• Encapsulation (computer science)
• Public interface
• Interface (Java)
• Application programming interface
• Interface (computing)
• List of basic computer science topics