Façade vs. Mediator

Question

I\'ve been researching the difference between these two patterns.

I understand that facade encapsulates access to a sub system and mediator encapsulates the interac

Answer 1

I'm using mediator to add log file functionality.

It works like this:

• Obj A tells the mediator it needs something done.
• The mediator sends the message to various client objects.
• Obj B does the thing Obj A needs, and sends an appropriate message back via the mediator.
• Meanwhile, Obj C is also sent both messages by the mediator, and logs the results. That way, we can get user statistics from the log files.
• Obj D could be an error checker as well, so that if Obj B responds that Obj A's request is impossible, Obj D could be the thing that reports that to the user. Errors can now be logged in a different file than regular activity, and could use some other means to behave (beeping, whatever) that Obj A shouldn't really concern itself with.

Answer 2

From the "Design Patterns" book, the KEY of the Mediator pattern is described as follows: "It (a mediator) acts as a HUB of communication for widgets (i.e., 'a' group of interdependent objects)."

In other words, a mediator object is the sole superobject that knows all other objects in a group of collaborating objects and how they should interact with each other. All other objects should interact with the mediator object, instead of each other.

In contrast, a facade is a "unified interface" for a set of interfaces in a subsystem - for use by consumers of the subsystem - not among the components of the subsystem.