@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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https://docs.oracle.com/en/java/javase/21/docs/api/java.base/java/util/Observable.html
Observerinterface have been deprecated. The event model supported byObserverandObservableis quite limited, the order of notifications delivered byObservableis unspecified, and state changes are not in one-for-one correspondence with notifications. For a richer event model, consider using thejava.beanspackage. For reliable and ordered messaging among threads, consider using one of the concurrent data structures in thejava.util.concurrentpackage. For reactive streams style programming, see theFlowAPI.