* An observable object can have one or more observers. An observer * may be any object that implements interface {@code Observer}. After an * observable instance changes, an application calling the * {@code Observable}'s {@code notifyObservers} method * causes all of its observers to be notified of the change by a call * to their {@code update} method. *
* The order in which notifications will be delivered is unspecified. * The default implementation provided in the Observable class will * notify Observers in the order in which they registered interest, but * subclasses may change this order, use no guaranteed order, deliver * notifications on separate threads, or may guarantee that their * subclass follows this order, as they choose. *
* Note that this notification mechanism has nothing to do with threads * and is completely separate from the {@code wait} and {@code notify} * mechanism of class {@code Object}. *
* When an observable object is newly created, its set of observers is
* empty. Two observers are considered the same if and only if the
* {@code equals} method returns true for them.
*
* @author Chris Warth
* @see java.util.Observable#notifyObservers()
* @see java.util.Observable#notifyObservers(java.lang.Object)
* @see java.util.Observer
* @see java.util.Observer#update(java.util.Observable, java.lang.Object)
* @since 1.0
*
* @deprecated
* This class and the {@link Observer} interface have been deprecated.
* The event model supported by {@code Observer} and {@code Observable}
* is quite limited, the order of notifications delivered by
* {@code Observable} is unspecified, and state changes are not in
* one-for-one correspondence with notifications.
* For a richer event model, consider using the
* {@link java.beans} package. For reliable and ordered
* messaging among threads, consider using one of the concurrent data
* structures in the {@link java.util.concurrent} package.
* For reactive streams style programming, see the
* {@link java.util.concurrent.Flow} API.
*/
@Deprecated(since="9")
public class Observable {
private boolean changed = false;
private Vector
* Each observer has its {@code update} method called with two
* arguments: this observable object and {@code null}. In other
* words, this method is equivalent to:
*
* Each observer has its {@code update} method called with two
* arguments: this observable object and the {@code arg} argument.
*
* @param arg any object.
* @see java.util.Observable#clearChanged()
* @see java.util.Observable#hasChanged()
* @see java.util.Observer#update(java.util.Observable, java.lang.Object)
*/
public void notifyObservers(Object arg) {
/*
* 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
*/
// Android-changed: Call out to hasChanged() to figure out if something changes.
// Upstream code avoids calling the nonfinal hasChanged() from the synchronized block,
// but that would break compatibility for apps that override that method.
// if (!changed)
if (!hasChanged())
return;
arrLocal = obs.toArray();
clearChanged();
}
for (int i = arrLocal.length-1; i>=0; i--)
((Observer)arrLocal[i]).update(this, arg);
}
/**
* Clears the observer list so that this object no longer has any observers.
*/
public synchronized void deleteObservers() {
obs.removeAllElements();
}
/**
* Marks this {@code Observable} object as having been changed; the
* {@code hasChanged} method will now return {@code true}.
*/
protected synchronized void setChanged() {
changed = true;
}
/**
* 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 {@code hasChanged} method will now return {@code false}.
* This method is called automatically by the
* {@code notifyObservers} methods.
*
* @see java.util.Observable#notifyObservers()
* @see java.util.Observable#notifyObservers(java.lang.Object)
*/
protected synchronized void clearChanged() {
changed = false;
}
/**
* Tests if this object has changed.
*
* @return {@code true} if and only if the {@code setChanged}
* method has been called more recently than the
* {@code clearChanged} method on this object;
* {@code false} otherwise.
* @see java.util.Observable#clearChanged()
* @see java.util.Observable#setChanged()
*/
public synchronized boolean hasChanged() {
return changed;
}
/**
* Returns the number of observers of this {@code Observable} object.
*
* @return the number of observers of this object.
*/
public synchronized int countObservers() {
return obs.size();
}
}
{@code
* notifyObservers(null)}
*
* @see java.util.Observable#clearChanged()
* @see java.util.Observable#hasChanged()
* @see java.util.Observer#update(java.util.Observable, java.lang.Object)
*/
public void notifyObservers() {
notifyObservers(null);
}
/**
* If this object has changed, as indicated by the
* {@code hasChanged} method, then notify all of its observers
* and then call the {@code clearChanged} method to indicate
* that this object has no longer changed.
*