public interface Observer
Observer interface when it
 wants to be informed of changes in observable objects.Observable| Modifier and Type | Method and Description | 
|---|---|
| void | update(Observable o,
      Object arg)This method is called whenever the observed object is changed. | 
void update(Observable o, Object arg)
notifyObservers method to have all the object's
 observers notified of the change.o - the observable object.arg - an argument passed to the notifyObservers
                 method. Submit a bug or feature 
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