public interface Observer
Observe interface defines the notification API through which
 interested observers are notified of subject changes.
 In general, classes that are interested in being notified of state changes
 in subjects they reference should implement the Observer
 interface.UpdateMessage| Modifier and Type | Method and Description | 
|---|---|
void | 
update(java.lang.Object observed,
      UpdateMessage change)
Notification message. 
 | 
void update(java.lang.Object observed,
          UpdateMessage change)
observed - the subject whose state has changed.change - what has changed.