The Observable is similar to the event sources for the listeners. The difference is in the functionality of the Observable class. Its event broadcast mechanism is more complex. Class java.util.Observable Observable object may have any number of Observers. Whenever the Observable instance changes, it notifies all of its observers.
Notification is a two step process.
If the Observable's changed flag is true, then the update method notifies on all observers and sets the flag to false. The two step process, allows multiple and independent changes to use one update call to notify the observers. It also simplifies the process of rolling back complex changes before reaching the commit point. Adds an observer to the observer list. Counts the number of observers.