| Methods Summary |
|---|
| public synchronized void | addObserver(Observer o)Adds an observer to the set of observers for this object, provided
that it is not the same as some observer already in the set.
The order in which notifications will be delivered to multiple
observers is not specified. See the class comment.
if (o == null)
throw new NullPointerException();
if (!obs.contains(o)) {
obs.addElement(o);
}
|
| protected synchronized void | clearChanged()Indicates that this object has no longer changed, or that it has
already notified all of its observers of its most recent change,
so that the hasChanged method will now return false.
This method is called automatically by the
notifyObservers methods.
changed = false;
|
| public synchronized int | countObservers()Returns the number of observers of this Observable object.
return obs.size();
|
| public synchronized void | deleteObserver(Observer o)Deletes an observer from the set of observers of this object.
Passing null to this method will have no effect.
obs.removeElement(o);
|
| public synchronized void | deleteObservers()Clears the observer list so that this object no longer has any observers.
obs.removeAllElements();
|
| public synchronized boolean | hasChanged()Tests if this object has changed.
return changed;
|
| public void | notifyObservers()If this object has changed, as indicated by the
hasChanged method, then notify all of its observers
and then call the clearChanged method to
indicate that this object has no longer changed.
Each observer has its update method called with two
arguments: this observable object and null. In other
words, this method is equivalent to:
notifyObservers(null)
notifyObservers(null);
|
| public void | notifyObservers(java.lang.Object arg)If this object has changed, as indicated by the
hasChanged method, then notify all of its observers
and then call the clearChanged method to indicate
that this object has no longer changed.
Each observer has its update method called with two
arguments: this observable object and the arg argument.
/*
* a temporary array buffer, used as a snapshot of the state of
* current Observers.
*/
Object[] arrLocal;
synchronized (this) {
/* We don't want the Observer doing callbacks into
* arbitrary code while holding its own Monitor.
* The code where we extract each Observable from
* the Vector and store the state of the Observer
* needs synchronization, but notifying observers
* does not (should not). The worst result of any
* potential race-condition here is that:
* 1) a newly-added Observer will miss a
* notification in progress
* 2) a recently unregistered Observer will be
* wrongly notified when it doesn't care
*/
if (!changed)
return;
arrLocal = obs.toArray();
clearChanged();
}
for (int i = arrLocal.length-1; i>=0; i--)
((Observer)arrLocal[i]).update(this, arg);
|
| protected synchronized void | setChanged()Marks this Observable object as having been changed; the
hasChanged method will now return true.
changed = true;
|
