The Facade Pattern provides a unified interface to a set of interfaces in a subsystem. Facade defines a higher-level interface that makes the subsystem easier to use.
A facade not only simplifies an interface, it decouples a client from a subsystem of components.
Facades and adapters may wrap multiple classes, but a facade's intent is to simplify, while an
adapter's is to convert the interface to something different.
The principle of least knowledge - talk only to your immediate friends.
the principle tell us that we should only invoke methods that belong to:
- The object itself
- Objects passed in as a parameter to the method.
- Any objects the method creates or instantiates
- Any components of the object
Summarize:
- when you need to use an existing class and its interface is not the one you need, use an adapter
- when you need to simplify and unify a large interface or complex set of interfaces, use a facade.
- An adapter changes an interface into one a client expects.
- A facade decouples a client from a complex subsytem.
- Implementing an adapter may require little work or a great deal of work depending on the size and complexity of the target interface.
- Implementing a facade requires that we compose the facade with its subsystem and usedelegation to perform the work of the facade.