javax.swing.event

Class EventListenerList

java.lang.Object

javax.swing.event.EventListenerList

All Implemented Interfaces:

Serializable

public class EventListenerList
extends Object
implements Serializable

A utility class for keeping track of EventListeners.

Example for using this class:

 import java.util.EventListener;
 import javax.swing.event.EventListenerList;

 class Foo
 {
   protected final EventListenerList listeners = new EventListenerList();
   protected BarClosedEvent barClosedEvent = null;

   public void addBarListener(BarListener l)
   {
     listeners.add(BarListener.class, l);
   }

   public void removeBarListener(BarListener l)
   {
     listeners.remove(BarListener.class, l);
   }

   protected void fireBarClosedEvent()
   {
     Object[] l = listeners.getListenerList();

     for (int i = l.length - 2; i >= 0; i -= 2)
       if (l[i] == BarListener.class)
         {
           // Create the event on demand, when it is needed the first time.
           if (barClosedEvent == null)
             barClosedEvent = new BarClosedEvent(this);

           ((BarClosedListener) l[i + 1]).barClosed(barClosedEvent);
         }
   }
 }

See Also:

Serialized Form

Field Summary

Fields

Modifier and Type	Field and Description
protected Object[]	listenerList An array with all currently registered listeners.

Constructor Summary

Constructors

Constructor and Description
EventListenerList() EventListenerList constructor

Method Summary

Methods

Modifier and Type	Method and Description
<T extends EventListener> void	add(Class<T> t, T listener) Registers a listener of a specific type.
int	getListenerCount() Determines the number of listeners.
int	getListenerCount(Class<?> t) Determines the number of listeners of a particular class.
Object[]	getListenerList() Returns an array containing a sequence of listenerType/listener pairs, one for each listener.
<T extends EventListener> T[]	getListeners(Class<T> c) Retrieves the currently subscribed listeners of a particular type.
<T extends EventListener> void	remove(Class<T> t, T listener) Removes a listener of a specific type.
String	toString() Returns a string representation of this object that may be useful for debugging purposes.

Methods inherited from class java.lang.Object

clone, equals, finalize, getClass, hashCode, notify, notifyAll, wait, wait, wait

Field Detail

listenerList

protected transient Object[] listenerList

An array with all currently registered listeners. The array has twice as many elements as there are listeners. For an even integer i, listenerList[i] indicates the registered class, and listenerList[i + 1] is the listener.

Constructor Detail

EventListenerList

public EventListenerList()

EventListenerList constructor

Method Detail

add

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

Registers a listener of a specific type.

Parameters:

t - the type of the listener.

listener - the listener to add, which must be an instance of t, or of a subclass of t.

Throws:

IllegalArgumentException - if listener is not an instance of t (or a subclass thereof).

NullPointerException - if t is null.

getListenerCount

public int getListenerCount()

Determines the number of listeners.

getListenerCount

public int getListenerCount(Class<?> t)

Determines the number of listeners of a particular class.

Parameters:

t - the type of listeners to be counted. In order to get counted, a subscribed listener must be exactly of class t. Thus, subclasses of t will not be counted.

getListenerList

public Object[] getListenerList()

Returns an array containing a sequence of listenerType/listener pairs, one for each listener.

Returns:

An array containing the listener types and references.

getListeners

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

Retrieves the currently subscribed listeners of a particular type. For a listener to be returned, it must have been registered with exactly the type c; subclasses are not considered equal.

The returned array can always be cast to c[]. Since it is a newly allocated copy, the caller may arbitrarily modify the array.

Parameters:

c - the class which was passed to add(java.lang.Class<T>, T).

Returns:

an array of c whose elements are the currently subscribed listeners of the specified type. If there are no such listeners, an empty array is returned.

Throws:

ClassCastException - if c does not implement the EventListener interface.

NullPointerException - if c is null.

Since:

1.3

remove

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

Removes a listener of a specific type.

Parameters:

t - the type of the listener.

listener - the listener to remove, which must be an instance of t, or of a subclass of t.

Throws:

IllegalArgumentException - if listener is not an instance of t (or a subclass thereof).

NullPointerException - if t is null.

toString

public String toString()

Returns a string representation of this object that may be useful for debugging purposes.

Overrides:

toString in class Object

Returns:

the String representing this Object, which may be null

See Also:

Object.getClass(), Object.hashCode(), Class.getName(), Integer.toHexString(int)