javax.help.event
Class EventListenerList
java.lang.Object
javax.help.event.EventListenerList
- Serializable
public class EventListenerList
extends java.lang.Object
implements Serializable
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 a type-safe API (preferably conforming
to the JavaBeans specification) and methods that dispatch event notification
methods to appropriate Event Listeners on the list.
The main benefits this class provides are that it is relatively
cheap if there are no listeners, provides serialization for
eventlistener lists in a single place, and provides a degree of MT safety
(when used correctly).
Usage example:
If one is defining a class that sends out FooEvents, and 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 listenrList = new EventListnerList();
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 Method to the
appropriate method name (one firing method should exist for each
notification method in the FooListener interface).
Warning: Serialized objects of this class are not be compatible with
future Swing releases. The current serialization support is appropriate
for short term storage or RMI between Swing1.0 applications. It will
not be possible to load serialized Swing1.0 objects with future releases
of Swing. The JDK1.2 release of Swing will be the compatibility
baseline for the serialized form of Swing objects.
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 listenerList.
|
int | getListenerCount(Class t) - Returns the total number of listeners of the supplied type
for this listenerList.
|
Object[] | getListenerList() - This passes back the event listener list as an array
of ListenerType - listener pairs.
|
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.
|
listenerList
protected Object[] listenerList
add
public void add(Class t,
EventListener l)
Adds the listener as a listener of the specified type.
t
- The type of the listener to be added.l
- The listener to be added.
getListenerCount
public int getListenerCount()
Returns the total number of listeners for this listenerList.
getListenerCount
public int getListenerCount(Class t)
Returns the total number of listeners of the supplied type
for this listenerList.
getListenerList
public Object[] getListenerList()
This 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.
remove
public void remove(Class t,
EventListener l)
Removes the listener as a listener of the specified type. If the
listener for a given class does not exist in the list, it is ignored.
t
- The type of the listener to be removed.l
- The listener to be removed.
toString
public String toString()
Returns a string representation of the EventListenerList.