The facade pattern
The facade pattern is designed to provide a simple interface to a complex system of components. For complex tasks, we may need to interact with these objects directly, but there is often a typical usage for the system for which these complicated interactions aren't necessary. The facade pattern allows us to define a new object that encapsulates this typical usage of the system. Any time we want access to common functionality, we can use the single object's simplified interface. If another part of the project needs access to more complicated functionality, it is still able to interact with the system directly. The UML diagram for the facade pattern is really dependent on the subsystem, but in a cloudy way, it looks like this:
A facade is, in many ways, like an adapter. The primary difference is that a facade tries to abstract a simpler interface out of a complex one, while an adapter only tries to map one existing interface to another.
Let's write a simple facade for an email...
