Editing Decorator pattern (section)

=== UML class and sequence diagram ===
[[File:w3sDesign Decorator Design Pattern UML.jpg|frame|none|A sample UML class and sequence diagram for the Decorator design pattern. 
<ref>{{cite web|title=The Decorator design pattern - Structure and Collaboration|url=http://w3sdesign.com/?gr=s04&ugr=struct|website=w3sDesign.com|access-date=2017-08-12}}</ref>]]

In the above [[Unified Modeling Language|UML]] [[class diagram]], 
the abstract <code>Decorator</code> class maintains a reference (<code>component</code>) 
to the decorated object (<code>Component</code>) and forwards all requests to it
(<code>component.operation()</code>). 
This makes <code>Decorator</code> transparent (invisible) to clients of <code>Component</code>.

Subclasses (<code>Decorator1</code>,<code>Decorator2</code>) implement additional behavior
(<code>addBehavior()</code>) that should be added to the <code>Component</code> (before/after forwarding a request to it).
<br />
The sequence diagram 
shows the run-time interactions: The <code>Client</code> object 
works through <code>Decorator1</code> and <code>Decorator2</code> objects to
extend the functionality of a <code>Component1</code> object.
<br />
The <code>Client</code> calls <code>operation()</code> 
on <code>Decorator1</code>, which forwards the request to <code>Decorator2</code>.
<code>Decorator2</code> performs <code>addBehavior()</code> after forwarding 
the request to <code>Component1</code> and returns to
<code>Decorator1</code>, which performs <code>addBehavior()</code>  
and returns to the <code>Client</code>.