Editing Command pattern (section)

==Overview==
The command<ref name="GoF">{{cite book |author=Erich Gamma |author2=Richard Helm |author3=Ralph Johnson |author4=John Vlissides|title=Design Patterns: Elements of Reusable Object-Oriented Software|year=1994|publisher=Addison Wesley|isbn=0-201-63361-2|pages=[https://archive.org/details/designpatternsel00gamm/page/233 233ff]|url-access=registration|url=https://archive.org/details/designpatternsel00gamm/page/233}}</ref>
design pattern is one of the twenty-three well-known ''[[Design Patterns|GoF design patterns]]'' that describe how to solve recurring design problems to design flexible and reusable object-oriented software, that is, objects that are easier to implement, change, test, and reuse.

Using the command design pattern can solve these problems:<ref>{{cite web |title=The Command design pattern - Problem, Solution, and Applicability |url=http://w3sdesign.com/?gr=b02&ugr=proble |access-date=2017-08-12 |website=w3sDesign.com |archive-date=2020-09-23 |archive-url=https://web.archive.org/web/20200923124858/http://w3sdesign.com/?gr=b02&ugr=proble |url-status=dead }}</ref>
* Coupling the invoker of a request to a particular request should be avoided. That is, hard-wired requests should be avoided.
* It should be possible to configure an object (that invokes a request) with a request.

Implementing (hard-wiring) a request directly into a class is inflexible because it couples the class to a particular request at compile-time, which makes it impossible to specify a request at run-time.

Using the command design pattern describes the following solution:

* Define separate (command) objects that encapsulate a request.
* A class delegates a request to a command object instead of implementing a particular request directly.

This enables one to configure a class with a command object that is used to perform a request. The class is no longer coupled to a particular request and has no knowledge (is independent) of how the request is carried out.

See also the UML class and sequence diagram below.