An interface defines the interaction between certain modules.

Interface is a very general concept which refers to the interaction points of arbitrary modules:

• The interface of a class is defined by its public methods.
• The interface of a method is defined by its method signature.
• The interface of a subsystem is defined by the public (facade) classes.
• The interface of a network service is defined by a protocol.
• The interface of a hardware component is defined by pins, wires, signals, protocols, etc.
• A graphical user interface is defined by buttons, menus, text boxes, and other controls.

The interface defines how a module shall be used. There may be ways circumventing the interface and accessing internal parts of a module directly. This should be avoided (IH/E) but is sometimes done.

A module can be described as having a provided interface and a required interface.

• Module
• Application Programming Interface (API)
• Application Binary Interface (ABI)
• Service Provider Interface (SPI)

• Interface (computing)

An interface is a language construct of certain object-oriented programming languages resembling an abstract class without any implementation.

An interface is similar to a class but does not contain any attributes or implementations—just method signatures. Typically object-oriented programming languages use interfaces in order to avoid the problems of multiple inheritance, especially the diamond problem. In such languages a class can inherit from only one class but multiple interfaces. In that way there is only one implementation inherited.

There are interfaces in Java, C#, Object Pascal/Delphi and possibly also in other languages.

Note that in this wiki whenever the language construct is meant (and not the concept) interface shall be written using a monospace font: interface vs. interface.

java.util.Collection<E>:

public interface Collection<E> extends Iterable<E> 
{
    boolean add(E e);
    boolean addAll(Collection<? extends E> c)
    void clear()
    boolean contains(Object o)
    ...
}

• Class
• Abstract Class
• Mixin

• In Object Pascal a unit, i.e. a pas-file, typically contains an interface and an implementation section. The interface section lists the declarations which are visible outside the unit.

Discuss this wiki article and the term on the corresponding talk page.