Using CDI with EJB 3 - EJB 3 in Action - page 499

The beans that need to be notified may change over time and a new module might be ad-
ded to the application—obviously you don't want to edit the BidController each time.
The ItemController therefore fires an event, which other beans, including Land-
ingController and TwitterNotifier , are listening to and waiting to act upon.
Using CDI's form of the observer pattern results in code with low coupling— ItemCon-
troller doesn't have a reference to these other beans, and the other beans that are listen-
ing don't need to acquire a reference to ItemController to receive events. Figure 12.4
illustrates the event-delivery process.
Figure 12.4. Events triggered by addItem