Friday, February 5, 2010
Observer Pattern
Observer Pattern
Participants : Observer,Subject
An observer listens to the changes that happen to an observable subject.
Observer pattern is useful when a notification is to be sent to a group of objects when any state change happens to a subject.
Objects which listen to the state changes of a subject is called Observer.
Java provides the following classes to implement a Observer design pattern
java.util.Observable - The subject should extend this class
java.util.Observer - The observer/listener class should extend this class
useful methods are
java.util.Observable
addObserver - to add a new observer
deleteObserver - to delete an observer
setChanged - to mark the subject as changed
notifyObservers - to notify the observers about state change
java.util.Observer
update - called whenever the observed method is changed
Participants : Observer,Subject
An observer listens to the changes that happen to an observable subject.
Observer pattern is useful when a notification is to be sent to a group of objects when any state change happens to a subject.
Objects which listen to the state changes of a subject is called Observer.
Java provides the following classes to implement a Observer design pattern
java.util.Observable - The subject should extend this class
java.util.Observer - The observer/listener class should extend this class
useful methods are
java.util.Observable
addObserver - to add a new observer
deleteObserver - to delete an observer
setChanged - to mark the subject as changed
notifyObservers - to notify the observers about state change
java.util.Observer
update - called whenever the observed method is changed
Labels: Design Pattern, Observer
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