Lecture overview -- Keyboard shortcut: 'u'  Previous page: A Composite Example: A GUI  -- Keyboard shortcut: 'p'  Next page: Cloning -- Keyboard shortcut: 'n'  Lecture notes - all slides together  Annotated slide -- Keyboard shortcut: 't'  Textbook -- Keyboard shortcut: 'v'  Alphabetic index  Help page about these notes  Course home    Abstract classes, Interfaces, and Patterns - slide 30 : 41

The Observer pattern revisited
It adds flexibility to the Observer pattern if an Observer implements the interface IObserver
A WeatherCenter (subject) and Watcher (observer) with interfaces.
Application of the two different Watchers.
Output of the WeatherCenter and Watchers application.
The IObserver interface captures the only necessary property of a class that plays the role as an observer