OpenJDK 27 · javax.swing.event.EventListenerList · APIdia, the JavaDoc alternative

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 responsibility 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 JavaBeans has been added to the java.beans package. Please see java.beans.XMLEncoder.

Field Summary

Modifier and Type	Field and Description
protected transient volatile Object[]	listenerList The list of ListenerType - Listener pairs
private static final Object[]	NULL_ARRAY

Constructor Summary

Access	Constructor and Description
public	EventListenerList() Constructs a `EventListenerList`.

Method Summary

Modifier and Type	Method and Description
public synchronized < the type of `EventListener` to add T extends EventListener> void	add(Class<T> the type of the `EventListener` class to add t, T the listener to be added l) Adds the listener as a listener of the specified type.
public int	Returns: an integer count of total number of listeners getListenerCount() Returns the total number of listeners for this listener list.
public int	Returns: the number of listeners of type `t` getListenerCount(Class<?> the type of listeners to count t) Returns the total number of listeners of the supplied type for this listener list.
private int	getListenerCount(Object[] list, Class<?> t)
public Object[]	Returns: array of ListenerType-listener pairs getListenerList() Passes back the event listener list as an array of ListenerType-listener pairs.
public < the type of `EventListener` to search for T extends EventListener> T[]	Returns: all of the listeners of the specified type. getListeners(Class<T> the type of `EventListener` classes to be returned t) Return an array of all the listeners of the given type.
private void	readObject(ObjectInputStream s)
public synchronized < the type of `EventListener` T extends EventListener> void	remove(Class<T> the type of the listener to be removed t, T the listener to be removed l) Removes the listener as a listener of the specified type.
public String	toString() Overrides java.lang.Object.toString. Returns a string representation of the EventListenerList.
private void	writeObject(ObjectOutputStream s)

Inherited from java.lang.Object:: clone equals finalize getClass hashCode notify notifyAll wait wait wait

Field Detail

listenerList	back to summary
protected transient volatile Object[] listenerList The list of ListenerType - Listener pairs

NULL_ARRAY	back to summary
private static final Object[] NULL_ARRAY

Constructor Detail

EventListenerList	back to summary
public EventListenerList() Constructs a `EventListenerList`.

Method Detail

add back to summary

add	back to summary
public synchronized <T extends EventListener> void add(Class<T> t, T l) Adds the listener as a listener of the specified type. Parameters <T> the type of `EventListener` to add t:Class<T> the type of the `EventListener` class to add l:T the listener to be added

public synchronized <T extends EventListener> void add(Class<T> t, T l)

Adds the listener as a listener of the specified type.

Parameters

<T>: the type of EventListener to add
t:Class<T>: the type of the EventListener class to add
l:T: the listener to be added

getListenerCount	back to summary
public int getListenerCount() Returns the total number of listeners for this listener list. Returns:int an integer count of total number of listeners

getListenerCount

back to summary

public int getListenerCount()

Returns the total number of listeners for this listener list.

Returns:int: an integer count of total number of listeners

getListenerCount back to summary

getListenerCount	back to summary
public int getListenerCount(Class<?> t) Returns the total number of listeners of the supplied type for this listener list. Parameters t:Class<?> the type of listeners to count Returns:int the number of listeners of type `t`

public int getListenerCount(Class<?> t)

Returns the total number of listeners of the supplied type for this listener list.

Parameters

t:Class<?>: the type of listeners to count

Returns:int

the number of listeners of type t

getListenerCount	back to summary
private int getListenerCount(Object[] list, Class<?> t)

getListenerList	back to summary
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. Returns:Object[] array of ListenerType-listener pairs

getListenerList

back to summary

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.

Returns:Object[]: array of ListenerType-listener pairs

getListeners back to summary

getListeners	back to summary
public <T extends EventListener> T[] getListeners(Class<T> t) Return an array of all the listeners of the given type. Parameters <T> the type of `EventListener` to search for t:Class<T> the type of `EventListener` classes to be returned Returns:T[] all of the listeners of the specified type. Exceptions ClassCastException: if the supplied class is not assignable to EventListener Since 1.3

public <T extends EventListener> T[] getListeners(Class<T> t)

Return an array of all the listeners of the given type.

Parameters

<T>: the type of EventListener to search for
t:Class<T>: the type of EventListener classes to be returned

Returns:T[]

all of the listeners of the specified type.

Exceptions

ClassCastException:: if the supplied class is not assignable to EventListener

Since

1.3

readObject	back to summary
private void readObject(ObjectInputStream s) throws IOException, ClassNotFoundException Annotations @Serial

remove back to summary

remove	back to summary
public synchronized <T extends EventListener> void remove(Class<T> t, T l) Removes the listener as a listener of the specified type. Parameters <T> the type of `EventListener` t:Class<T> the type of the listener to be removed l:T the listener to be removed

public synchronized <T extends EventListener> void remove(Class<T> t, T l)

Removes the listener as a listener of the specified type.

Parameters

<T>: the type of EventListener
t:Class<T>: the type of the listener to be removed
l:T: the listener to be removed

toString	back to summary
public String toString() Overrides java.lang.Object.toString. Returns a string representation of the EventListenerList.

toString

back to summary

public String toString()

Overrides java.lang.Object.toString.

Returns a string representation of the EventListenerList.

writeObject	back to summary
private void writeObject(ObjectOutputStream s) throws IOException Annotations @Serial

public Class EventListenerList

Field Summary

Constructor Summary

Method Summary

Field Detail

Constructor Detail

Method Detail