Class Observable
- java.lang.Object
-
- java.util.Observable
@Deprecated(since="9") public class Observable extends Object
Observer
interface have been deprecated. The event model supported by Observer
and Observable
is quite limited, the order of notifications delivered by Observable
is unspecified, and state changes are not in one-for-one correspondence with notifications. For a richer event model, consider using the java.beans
package. For reliable and ordered messaging among threads, consider using one of the concurrent data structures in the java.util.concurrent
package. For reactive streams style programming, see the Flow
API.This class represents an observable object, or "data" in the model-view paradigm. It can be subclassed to represent an object that the application wants to have observed.
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.
- Since:
- 1.0
- See Also:
-
notifyObservers()
,notifyObservers(java.lang.Object)
,Observer
,Observer.update(java.util.Observable, java.lang.Object)
Constructor Summary
Constructor | Description |
---|---|
Observable() | Deprecated. Construct an Observable with zero Observers. |
Method Summary
Modifier and Type | Method | Description |
---|---|---|
void | addObserver(Observer o) | 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 |
int | countObservers() | Deprecated. Returns the number of observers of this |
void | deleteObserver(Observer o) | 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 |
void | notifyObservers(Object arg) | Deprecated. If this object has changed, as indicated by the |
protected void | setChanged() | Deprecated. Marks this |
Methods declared in class java.lang.Object
clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait
Constructor Detail
Observable
public Observable()
Construct an Observable with zero Observers.
Method Detail
addObserver
public 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.
- Parameters:
-
o
- an observer to be added. - Throws:
-
NullPointerException
- if the parameter o is null.
deleteObserver
public void deleteObserver(Observer o)
Deletes an observer from the set of observers of this object. Passing null
to this method will have no effect.
- Parameters:
-
o
- the observer to be deleted.
notifyObservers
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
public void notifyObservers(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.
- Parameters:
-
arg
- any object. - See Also:
-
clearChanged()
,hasChanged()
,Observer.update(java.util.Observable, java.lang.Object)
deleteObservers
public void deleteObservers()
Clears the observer list so that this object no longer has any observers.
setChanged
protected void setChanged()
Marks this Observable
object as having been changed; the hasChanged
method will now return true
.
clearChanged
protected 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.
hasChanged
public boolean hasChanged()
Tests if this object has changed.
- Returns:
-
true
if and only if thesetChanged
method has been called more recently than theclearChanged
method on this object;false
otherwise. - See Also:
-
clearChanged()
,setChanged()
countObservers
public int countObservers()
Returns the number of observers of this Observable
object.
- Returns:
- the number of observers of this object.