Editing Proxy pattern (section)

==Overview==
The Proxy 
<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/207 207ff]|url-access=registration|url=https://archive.org/details/designpatternsel00gamm/page/207}}</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 Proxy design pattern solve?===
Source:<ref>{{cite web|title=The Proxy design pattern - Problem, Solution, and Applicability|url=http://w3sdesign.com/?gr=s07&ugr=proble|website=w3sDesign.com|access-date=2017-08-12}}</ref>
* The access to an object should be controlled.
* Additional functionality should be provided when accessing an object.

When accessing sensitive objects, for example, it should be possible to check that clients have the needed access rights.

===What solution does the Proxy design pattern describe?===

Define a separate <code>Proxy</code> object that 
* can be used as a substitute for another object (<code>Subject</code>), and 
* implements additional functionality to control the access to this subject.

This makes it possible to work through a <code>Proxy</code> object to perform additional functionality when accessing a subject, like checking the access rights of clients accessing a sensitive object.

To act as a substitute for a subject, a proxy must implement the <code>Subject</code> interface. Clients can't tell whether they work with a subject or its proxy.
 
See also the UML class and sequence diagram below.