EventListenerListpublic class EventListenerList extends Object implements SerializableA 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. As of 1.4, support for long term storage
of all JavaBeansTM
has been added to the java.beans package.
Please see {@link java.beans.XMLEncoder}. |
| Fields Summary |
|---|
| private static final Object[] | NULL_ARRAY | | protected transient Object[] | listenerList |
| Methods Summary |
|---|
| public synchronized void | add(java.lang.Class t, T l)Adds the listener as a listener of the specified type.
if (l==null) {
// In an ideal world, we would do an assertion here
// to help developers know they are probably doing
// something wrong
return;
}
if (!t.isInstance(l)) {
throw new IllegalArgumentException("Listener " + l +
" is not of type " + t);
}
if (listenerList == NULL_ARRAY) {
// if this is the first listener added,
// initialize the lists
listenerList = new Object[] { t, l };
} else {
// Otherwise copy the array and add the new listener
int i = listenerList.length;
Object[] tmp = new Object[i+2];
System.arraycopy(listenerList, 0, tmp, 0, i);
tmp[i] = t;
tmp[i+1] = l;
listenerList = tmp;
}
| | public int | getListenerCount()Returns the total number of listeners for this listener list.
return listenerList.length/2;
| | public int | getListenerCount(java.lang.Class t)Returns the total number of listeners of the supplied type
for this listener list.
Object[] lList = listenerList;
return getListenerCount(lList, t);
| | private int | getListenerCount(java.lang.Object[] list, java.lang.Class t)
int count = 0;
for (int i = 0; i < list.length; i+=2) {
if (t == (Class)list[i])
count++;
}
return count;
| | public java.lang.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.
return listenerList;
| | public T[] | getListeners(java.lang.Class t)Return an array of all the listeners of the given type.
Object[] lList = listenerList;
int n = getListenerCount(lList, t);
T[] result = (T[])Array.newInstance(t, n);
int j = 0;
for (int i = lList.length-2; i>=0; i-=2) {
if (lList[i] == t) {
result[j++] = (T)lList[i+1];
}
}
return result;
| | private void | readObject(java.io.ObjectInputStream s)
listenerList = NULL_ARRAY;
s.defaultReadObject();
Object listenerTypeOrNull;
while (null != (listenerTypeOrNull = s.readObject())) {
ClassLoader cl = Thread.currentThread().getContextClassLoader();
EventListener l = (EventListener)s.readObject();
add((Class<EventListener>)Class.forName((String)listenerTypeOrNull, true, cl), l);
}
| | public synchronized void | remove(java.lang.Class t, T l)Removes the listener as a listener of the specified type.
if (l ==null) {
// In an ideal world, we would do an assertion here
// to help developers know they are probably doing
// something wrong
return;
}
if (!t.isInstance(l)) {
throw new IllegalArgumentException("Listener " + l +
" is not of type " + t);
}
// Is l on the list?
int index = -1;
for (int i = listenerList.length-2; i>=0; i-=2) {
if ((listenerList[i]==t) && (listenerList[i+1].equals(l) == true)) {
index = i;
break;
}
}
// If so, remove it
if (index != -1) {
Object[] tmp = new Object[listenerList.length-2];
// Copy the list up to index
System.arraycopy(listenerList, 0, tmp, 0, index);
// Copy from two past the index, up to
// the end of tmp (which is two elements
// shorter than the old list)
if (index < tmp.length)
System.arraycopy(listenerList, index+2, tmp, index,
tmp.length - index);
// set the listener array to the new array or null
listenerList = (tmp.length == 0) ? NULL_ARRAY : tmp;
}
| | public java.lang.String | toString()Returns a string representation of the EventListenerList.
Object[] lList = listenerList;
String s = "EventListenerList: ";
s += lList.length/2 + " listeners: ";
for (int i = 0 ; i <= lList.length-2 ; i+=2) {
s += " type " + ((Class)lList[i]).getName();
s += " listener " + lList[i+1];
}
return s;
| | private void | writeObject(java.io.ObjectOutputStream s)
Object[] lList = listenerList;
s.defaultWriteObject();
// Save the non-null event listeners:
for (int i = 0; i < lList.length; i+=2) {
Class t = (Class)lList[i];
EventListener l = (EventListener)lList[i+1];
if ((l!=null) && (l instanceof Serializable)) {
s.writeObject(t.getName());
s.writeObject(l);
}
}
s.writeObject(null);
|
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