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java.lang.Objectorg.crosswire.common.util.EventListenerList
public class EventListenerList
A class which holds a list of EventListeners. This code is lifted from javax.sw*ng.event.EventListnerList. It is very useful in non GUI code which does not need the rest of sw*ng. BORROWED: From javax.sw*ng.event.EventListnerList
If you inculde sw*ng code in non-gui code then you can end up not being able to run your code in a headerless environment because X includes Y which inculdes Font which tries to lookup font metrics and then everything dies. I appreciate the Headerless changes in 1.4, but my rule (from before 1.4) was "Don't inculde sw*ng code from non-sw*ng code", and I enforced that by making sure all my sw*ng code was in a package with sw*ng in the name and by making sure that the word sw*ng was not in any non-sw*ng code (hence I spelled it sw*ng in comments) That way some simple greps will tell you if the servlet front end was likely to die.
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 which this class provides are that it is relatively cheap in the case of no listeners, and provides serialization for eventlistener lists in a single place, as well as a degree of MT safety (when used correctly). Usage example: Say one is defining a class which sends out FooEvents, and wantds 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 fire method should exist for each notification method in the FooListener interface).
Warning: Serialized objects of this class will not be compatible with future Sw*ng releases. The current serialization support is appropriate for short term storage or RMI between applications running the same version of Sw*ng. A future release of Sw*ng will provide support for long term persistence.
Field Summary | |
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protected Object[] |
listenerList
The list of ListenerType - Listener pairs |
private static Object[] |
NULL_ARRAY
A null array to be shared by all empty listener lists |
private static long |
serialVersionUID
Serialization ID |
Constructor Summary | |
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EventListenerList()
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Method Summary | |
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void |
add(Class t,
EventListener li)
Add 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. |
private int |
getListenerCount(Object[] list,
Class t)
|
Object[] |
getListenerList()
This 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. |
private void |
readObject(ObjectInputStream ois)
Serialization support |
void |
remove(Class t,
EventListener li)
Remove the listener as a listener of the specified type. |
String |
toString()
Return a string representation of the EventListenerList. |
private void |
writeObject(ObjectOutputStream oos)
Serialization support |
Methods inherited from class java.lang.Object |
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clone, equals, finalize, getClass, hashCode, notify, notifyAll, wait, wait, wait |
Field Detail |
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private static final Object[] NULL_ARRAY
protected transient Object[] listenerList
private static final long serialVersionUID
Constructor Detail |
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public EventListenerList()
Method Detail |
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public Object[] getListenerList()
public EventListener[] getListeners(Class t)
ClassCastException
- if the supplied class
is not assignable to EventListenerpublic int getListenerCount()
public int getListenerCount(Class t)
private int getListenerCount(Object[] list, Class t)
public void add(Class t, EventListener li)
t
- the type of the listener to be addedli
- the listener to be addedpublic void remove(Class t, EventListener li)
t
- the type of the listener to be removedli
- the listener to be removedprivate void writeObject(ObjectOutputStream oos) throws IOException
IOException
private void readObject(ObjectInputStream ois) throws IOException, ClassNotFoundException
IOException
ClassNotFoundException
public String toString()
toString
in class Object
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Copyright ? 2003-2006 | |||||||||
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