Editing Facade pattern (section)

==Overview== 
The Facade
<ref name="GoF">{{cite book|author=Erich Gamma, Richard Helm, Ralph Johnson, 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/185 185ff]|url-access=registration|url=https://archive.org/details/designpatternsel00gamm/page/185}}</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.

What problems can the Facade design pattern solve?
<ref>{{cite web|title=The Facade design pattern - Problem, Solution, and Applicability|url=http://w3sdesign.com/?gr=s05&ugr=proble|website=w3sDesign.com|access-date=2017-08-12}}</ref>

* To make a complex subsystem easier to use, a simple interface should be provided for a set of interfaces in the subsystem.
* The dependencies on a subsystem should be minimized.

Clients that access a complex subsystem directly refer to (depend on) many different objects having different interfaces (tight coupling), which makes the clients hard to implement, change, test, and reuse.

What solution does the Facade design pattern describe?

Define a <code>Facade</code> object that 
* implements a simple interface in terms of (by delegating to) the interfaces in the subsystem and
* may perform additional functionality before/after forwarding a request.

This enables to work through a <code>Facade</code> object to minimize the dependencies on a subsystem.
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See also the UML class and sequence diagram below.