Observer (aka Listener)

I used to use "Google Reader" to keep informed about development news.
It's a simple & free RSS reader with a mobile & web interfaces.
With it, I can subscribe to RSS feeds that I wish.
I am directly informed of these news & events.
I can choose to read to full article or do nothing.

THIS IS THE OBSERVER DESIGN PATTERN !!!

When you will be in the same situation =
You want to keep informed of changes but to choose to act or not.

Don't make objects asking if changes happened, just make observers !!!

The observers will implement an Observer interface.
The observable objects will implement an Observable interface.
The observers will be able to be referenced to the Observable objects.
The observers will be notified when an event will happen.