Facade Pattern
Most of the times you will find yourself structuring the codebase into multiple subsystems, each subsystem has a few modules, and of course when trying to consume a subsystem functionality in any place in your code you'll find that it needs a few complex calls and operations to the subsystem internal modules.
Intent
Provide a simple, unified interface to a set of interfaces in a subsystem. Facade defines a higher-level interface (more complex body) that make the subsystems easier to use and consume.
When to use
When you need to have a limited but straightforward interface to a complex subsystem.
When there are many dependencies between client code and the subsystem classes, so a facade is introduced to decouple the client from the subsystem.
When you want to layer your subsystems, a facade can be used as an entry point to each level of the subsystem.
Structure
Facade: knows the subsystem classes and what they're responsible for, and delegates the client requests to the appropriate objects in the appropriate order.
Subsystem Classes: they're the classes that form the subsystem (either a pre-existing package, a 3rd-party library or an API).
Note
Remember that Facade pattern can easily become a god object with a lot of tightly coupled dependencies.
Examples
Source Code | UML |
You can find the tests here.
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