Questions tagged [interface]

An interface is the designated point of interaction with a component.

Well-defined, comprehensive, versatile but still minimal interfaces are critical for reliability, extensibility, maintainance, and compatibility.

In programming, we mostly encounter:

• apis, which consist of symbols (types (and all they might entail), functions, constants, variables, templates, namespaces and so on), and their defined behavior, which might include their own turing-complete languages.
• abis, which define the mapping of APIs to the underlying machine.
• protocols, which define interactions over a connection, network, or the like.
• And many combined ones, especially in directly interacing with a device, for example to write a device-driver.

In some languages, mostly object-oriented single-inheritance ones, an interface is a restricted type not containing any state nor instantiable by itself, and only able to inherit from (any number of) other interfaces.
A class can implement any number of interfaces in addition to inheriting from a single other class (most of those languages enforce a single-root inheritance-hierarchy).
Most insist that the base-class is listed first, and some allow explicitly implementing an interfaces members, which makes them inaccessible except through an interface-pointer of that type.

The implementation of an interface varies between programming languages and environments; for e.g. C# has the following definition (Interfaces (C# Programming Guide));

Interfaces describe a group of related functionalities that can belong to any class or struct. You define an interface by using the interface keyword, as shown in the following example.

interface IEquatable<T> {
  bool Equals(T obj);
}

An interface may or may not contain or make use of any number of interfaces or their equivalent.

You can "program to the interface, not the implementation" without using any interface, as well as fail to but still use interfaces all over the place.

The [interface]-tag should should be used in conjunction with the appropriate [language]-tag(s) where applicable.