Facade Pattern

What?

• a facade encapsulates a complex subsystem behind a simple interface. It hides much of the complexity and makes the subsystem easy to use.

• Used for complex complex systems of clases, libraries or frameworks

• Recognised by the use of a simple interface, but under the hood (implementation) is complex

• The client only interacts with the Façade class without knowing about the subsystem classes.

• The subsystem that the facade abstracts over doesnot know anything (not dependent) about the facade

Why?

• Layering: Facade pattern can be used in applications for creating a layer to abstract and unify the related interfaces in the application. Use of a facade will define an entry point to each subsystem level and thus make them communicate only through their facades; this can simplify the dependencies between them.

Benefits

• It decouples a client implementation from the complex subsystem.

  • we can make changes to the existing subsystem and don't affect a client.

• Façade makes the API and libraries easier to use which is good for maintenance and readability.

• It can collate and abstract various poorly designed APIs with a single simplified API.

• It reduces dependencies of the external code on the inner working of the libraries and thus providing flexibility.

• increases loose coupling

Drawbacks

• Lead to lots of levels of abstraction and indirection

• Can be overused for simple implementations

• the subsystem methods are connected to the Façade layer. If the structure of the subsystem changes then it will require subsequent change to the Façade layer and client methods.