Editing Class (computer programming) (section)

=== Class interface ===
{{main|Interface (object-oriented programming)}}
{{Further|Interface (computing)}}

Every class ''implements'' (or ''realizes'') an interface by providing [[#Structure|structure]] and behavior. Structure consists of data and state, and behavior consists of code that specifies how methods are implemented.{{sfn|Booch|1994|p=105}} There is a distinction between the definition of an interface and the implementation of that interface; however, this line is blurred in many programming languages because class declarations both define and implement an interface. Some languages, however, provide features that separate interface and implementation. For example, an [[#Abstract_and_Concrete|abstract class]] can define an interface without providing an implementation.

Languages that support class inheritance also allow classes to inherit interfaces from the classes that they are derived from.

For example, if "class A" inherits from "class B" and if "class B" implements the interface "interface B" then "class A" also inherits the functionality(constants and methods declaration) provided by "interface B".

In languages that support [[#Information hiding and encapsulation|access specifiers]], the interface of a class is considered to be the set of public members of the class, including both methods and attributes (via implicit [[Mutator method|getter and setter methods]]); any private members or internal data structures are not intended to be depended on by external<!--client--> code and thus are not part of the interface.

Object-oriented programming methodology<!--is designed in such a way--> dictates that the operations of any interface of a class are to be independent of each other. It results in a layered design where clients of an interface use the methods declared in the interface. An interface places no requirements for clients to invoke the operations of one interface in any particular order. This approach has the benefit that client code can assume that the operations of an interface are available for use whenever the client<!--holds a valid reference--> has access to the object.<ref>{{Cite book|title=New Perspectives on Computer Concepts 2016, Comprehensive |publisher= Cengage Learning |last=Parsons |first= June Jamrich|isbn=9781305271616|location=Boston, MA|oclc=917155105|date=2015-06-22}}</ref> 

; Class interface example
The buttons on the front of your television set are the interface between you and the electrical wiring on the other side of its plastic casing. You press the "power" button to toggle the television on and off. In this example, your particular television is the instance, each method is represented by a button, and all the buttons together compose the interface (other television sets that are the same model as yours would have the same interface). In its most common form, an interface is a specification of a group of related methods without any associated implementation of the methods.

A television set also has a myriad of ''attributes'', such as size and whether it supports color, which together comprise its structure. A class represents the full description of a television, including its attributes (structure) and buttons (interface).

Getting the total number of televisions manufactured could be a ''static method'' of the television class. This method is associated with the class, yet is outside the domain of each instance of the class. A static method that finds a particular instance out of the set of all television objects is another example.