Interface (object-oriented programming)

Short description: Abstraction of a class

In object-oriented programming, an interface or protocol type^{[lower-alpha 1]} is a data type that acts as an abstraction of a class. It describes a set of method signatures, the implementations of which may be provided by multiple classes that are otherwise not necessarily related to each other.^[1] A class which provides the methods listed in a protocol is said to adopt the protocol,^[2] or to implement the interface.^[1]

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, 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 languages provide explicit language support for protocols (Ada, C#, D, Dart, Delphi, Go, Java, Logtalk, Object Pascal, Objective-C, OCaml, PHP, Racket, Seed7, Swift, Python 3.8). In languages supporting multiple inheritance, such as C++, interfaces are implemented as abstract classes.

In languages without explicit support, protocols are often still present as conventions. This is known as duck typing. For example, in Python, any class can implement an __iter__ method and be used as a collection.^[3]

Type classes in languages like Haskell, or module signatures in ML and OCaml, are used for many of the things that protocols are used for.^{[clarification needed]}

In Rust, interfaces are called traits.^[4]

Notes

↑ Usage of these terms varies by programming language. Java and languages derived from it tend to use "interface", while "protocol" is generally more popular elsewhere.

References

↑ ^1.0 ^1.1 "Interfaces - define behavior for multiple types" (in en-us). https://learn.microsoft.com/en-us/dotnet/csharp/fundamentals/types/interfaces.
↑ Miller, BJ (2015). Sams Teach Yourself Swift in 24 hours. Indianapolis, Indiana. p. 263. ISBN 978-0-672-33724-6. "Any type can adopt a protocol to help give it extra functionality to accomplish a particular set of tasks."
↑ "Glossary — Python 3.11.0 documentation". https://docs.python.org/3/glossary.html#term-iterable.
↑ "Traits - The Rust Reference". January 2024. https://doc.rust-lang.org/reference/items/traits.html.

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[1] Usage of these terms varies by programming language. Java and languages derived from it tend to use "interface", while "protocol" is generally more popular elsewhere.

[csharp-learn-2] 1.0 ^1.1 "Interfaces - define behavior for multiple types" (in en-us). https://learn.microsoft.com/en-us/dotnet/csharp/fundamentals/types/interfaces.

[swift-24h-3] Miller, BJ (2015). Sams Teach Yourself Swift in 24 hours. Indianapolis, Indiana. p. 263. ISBN 978-0-672-33724-6. "Any type can adopt a protocol to help give it extra functionality to accomplish a particular set of tasks."

[python-iter-4] "Glossary — Python 3.11.0 documentation". https://docs.python.org/3/glossary.html#term-iterable.

[5] "Traits - The Rust Reference". January 2024. https://doc.rust-lang.org/reference/items/traits.html.

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v t e Data types
Uninterpreted	Bit Byte Trit Tryte Word Bit array
Numeric	Arbitrary-precision or bignum Complex Decimal Fixed point Floating point Double precision Extended precision Long double Octuple precision Quadruple precision Single precision Reduced precision Minifloat Half precision bfloat16 Integer signedness Interval Rational
Pointer	Address physical virtual Reference
Text	Character String null-terminated
Composite	Algebraic data type generalized Array Associative array Class Dependent Equality Inductive Intersection List Object metaobject Option type Product Record or Struct Refinement Set Union tagged
Other	Boolean Bottom type Collection Enumerated type Exception Function type Opaque data type Recursive data type Semaphore Stream Top type Type class Unit type Void
Related topics	Abstract data type Data structure Generic Kind metaclass Parametric polymorphism Primitive data type Protocol interface Subtyping Type constructor Type conversion Type system Type theory
See also platform-dependent and independent units of information

Interface (object-oriented programming)

See also

Notes

References