== Participants ==

<li>defines the abstraction's interface</li>

<li>maintains a reference to an object of type Implementor</li>

<li>extends the interface defined by Abstraction.</li>

<li>defines the interface for implementation classes. This interface does not have to correspond exactly to Abstraction's interface; in fact the two interfaces can be quite different. The Implementation interface provides only primitive operations, and Abstraction defines high-level operations based on these primitives.

<li>implements the Implementor interface and defines its concrete implementation.</li>

== Consequences ==