SE450: Facade Pattern [76/86]

Context

1. A subsystem consists of multiple classes, making it complicated for clients to use
   
2. Implementor may want to change subsystem classes
3. Want to give a coherent entry point
   

Solution

1. Define a facade class that exposes all capabilities of the subsystem as methods
2. The facade methods delegate requests to the subsystem classes
3. The subsystem classes do not know about the facade class