@Deprecated(since="9") public class Observable extends Object
An observable object can have one or more observers. An observer may be any object that implements interface Observer
. After an observable instance changes, an application calling the Observable
's notifyObservers
method causes all of its observers to be notified of the change by a call to their 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 wait
and notify
mechanism of class 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 equals
method returns true for them.
Constructor | Description |
---|---|
Observable() |
Deprecated. Construct an Observable with zero Observers. |
Modifier and Type | Method | Description |
---|---|---|
void |
addObserver |
Deprecated. 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. |
protected void |
clearChanged() |
Deprecated. 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 . |
int |
countObservers() |
Deprecated. Returns the number of observers of this Observable object. |
void |
deleteObserver |
Deprecated. Deletes an observer from the set of observers of this object. |
void |
deleteObservers() |
Deprecated. Clears the observer list so that this object no longer has any observers. |
boolean |
hasChanged() |
Deprecated. Tests if this object has changed. |
void |
notifyObservers() |
Deprecated. 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. |
void |
notifyObservers |
Deprecated. 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. |
protected void |
setChanged() |
Deprecated. Marks this Observable object as having been changed; the hasChanged method will now return true . |
public Observable()
public void addObserver(Observer o)
o
- an observer to be added.NullPointerException
- if the parameter o is null.public void deleteObserver(Observer o)
null
to this method will have no effect.o
- the observer to be deleted.public void notifyObservers()
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)
public void notifyObservers(Object arg)
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.
arg
- any object.public void deleteObservers()
protected void setChanged()
Observable
object as having been changed; the hasChanged
method will now return true
.protected void clearChanged()
hasChanged
method will now return false
. This method is called automatically by the notifyObservers
methods.public boolean hasChanged()
true
if and only if the setChanged
method has been called more recently than the clearChanged
method on this object; false
otherwise.public int countObservers()
Observable
object.
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Documentation extracted from Debian's OpenJDK Development Kit package.
Licensed under the GNU General Public License, version 2, with the Classpath Exception.
Various third party code in OpenJDK is licensed under different licenses (see Debian package).
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https://docs.oracle.com/en/java/javase/21/docs/api/java.base/java/util/Observable.html
Observer
interface have been deprecated. The event model supported byObserver
andObservable
is quite limited, the order of notifications delivered byObservable
is unspecified, and state changes are not in one-for-one correspondence with notifications. For a richer event model, consider using thejava.beans
package. For reliable and ordered messaging among threads, consider using one of the concurrent data structures in thejava.util.concurrent
package. For reactive streams style programming, see theFlow
API.