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JavaTM 2 Platform Std. Ed. v1.3.1 |
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javax.swing.event
Class EventListenerList
java.lang.Object | +--javax.swing.event.EventListenerList
- All Implemented Interfaces:
- Serializable
- public class EventListenerList
- extends Object
- implements Serializable
- extends Object
A class that holds a list of EventListeners. A single instance can be used to hold all listeners (of all types) for the instance using the list. It is the responsiblity of the class using the EventListenerList to provide type-safe API (preferably conforming to the JavaBeans spec) and methods which dispatch event notification methods to appropriate Event Listeners on the list. The main benefits that this class provides are that it is relatively cheap in the case of no listeners, and it provides serialization for event-listener lists in a single place, as well as a degree of MT safety (when used correctly). Usage example: Say one is defining a class that sends out FooEvents, and one wants to allow users of the class to register FooListeners and receive notification when FooEvents occur. The following should be added to the class definition:
EventListenerList listenerList = new EventListenerList();
FooEvent fooEvent = null;
public void addFooListener(FooListener l) {
listenerList.add(FooListener.class, l);
}
public void removeFooListener(FooListener l) {
listenerList.remove(FooListener.class, l);
}
// Notify all listeners that have registered interest for
// notification on this event type. The event instance
// is lazily created using the parameters passed into
// the fire method.
protected void fireFooXXX() {
// Guaranteed to return a non-null array
Object[] listeners = listenerList.getListenerList();
// Process the listeners last to first, notifying
// those that are interested in this event
for (int i = listeners.length-2; i>=0; i-=2) {
if (listeners[i]==FooListener.class) {
// Lazily create the event:
if (fooEvent == null)
fooEvent = new FooEvent(this);
((FooListener)listeners[i+1]).fooXXX(fooEvent);
}
}
}
foo should be changed to the appropriate name, and fireFooXxx to the
appropriate method name. One fire method should exist for each
notification method in the FooListener interface.
Warning: Serialized objects of this class will not be compatible with future Swing releases. The current serialization support is appropriate for short term storage or RMI between applications running the same version of Swing. A future release of Swing will provide support for long term persistence.
- See Also:
- Serialized Form
| Field Summary | |
protected Object[] |
listenerList
|
| Constructor Summary | |
EventListenerList()
|
|
| Method Summary | |
void |
add(Class t,
EventListener l)
Adds the listener as a listener of the specified type. |
int |
getListenerCount()
Returns the total number of listeners for this listener list. |
int |
getListenerCount(Class t)
Returns the total number of listeners of the supplied type for this listener list. |
Object[] |
getListenerList()
Passes back the event listener list as an array of ListenerType-listener pairs. |
EventListener[] |
getListeners(Class t)
Return an array of all the listeners of the given type. |
void |
remove(Class t,
EventListener l)
Removes the listener as a listener of the specified type. |
String |
toString()
Returns a string representation of the EventListenerList. |
| Methods inherited from class java.lang.Object |
clone, equals, finalize, getClass, hashCode, notify, notifyAll, wait, wait, wait |
| Field Detail |
listenerList
protected transient Object[] listenerList
| Constructor Detail |
EventListenerList
public EventListenerList()
| Method Detail |
getListenerList
public Object[] getListenerList()
- Passes back the event listener list as an array
of ListenerType-listener pairs. Note that for
performance reasons, this implementation passes back
the actual data structure in which the listener data
is stored internally!
This method is guaranteed to pass back a non-null
array, so that no null-checking is required in
fire methods. A zero-length array of Object should
be returned if there are currently no listeners.
WARNING!!! Absolutely NO modification of
the data contained in this array should be made -- if
any such manipulation is necessary, it should be done
on a copy of the array returned rather than the array
itself.
getListeners
public EventListener[] getListeners(Class t)
- Return an array of all the listeners of the given type.
- Since:
- 1.3
getListenerCount
public int getListenerCount()
- Returns the total number of listeners for this listener list.
getListenerCount
public int getListenerCount(Class t)
- Returns the total number of listeners of the supplied type
for this listener list.
add
public void add(Class t, EventListener l)
- Adds the listener as a listener of the specified type.
- Parameters:
t- the type of the listener to be addedl- the listener to be added
remove
public void remove(Class t, EventListener l)
- Removes the listener as a listener of the specified type.
- Parameters:
t- the type of the listener to be removedl- the listener to be removed
toString
public String toString()
- Returns a string representation of the EventListenerList.
- Following copied from class:
java.lang.Object- Returns:
- a string representation of the object.
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JavaTM 2 Platform Std. Ed. v1.3.1 |
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