observer type, a source can notify a observer class
add an observer to the source
add an observer to the source
want observe this source
false if the observer currently observe the source true otherwise
remove an observer to the source
remove an observer to the source
want to stop observer this source
false if the observer currently doesn't observer the source true otherwise
the observers attached to current source
fast way to add an observer
fast way to add an observer
want to observe current source
the source
notify all the observer
notify all the observer
the event generate
(Since version ) see corresponding Javadoc for more information.
define a generic event source