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From "Michael Wooten (JIRA)" <>
Subject [jira] Updated: (LANG-580) Add Event Support Utilities
Date Fri, 02 Jul 2010 11:07:50 GMT


Michael Wooten updated LANG-580:

    Attachment: commons-lang-event-support.patch

This patch adds a new package under lang3 called "event" and several new classes inside of
it. The patch adds the described "EventSupport" interface, as well as an abstract implementation
called AbstractEventSupport with documentation on how to subclass it. The patch also adds
the ReflectiveEventSupport class with support for firing events based on method name or Method

> Add Event Support Utilities
> ---------------------------
>                 Key: LANG-580
>                 URL:
>             Project: Commons Lang
>          Issue Type: New Feature
>          Components: General
>    Affects Versions: 3.0
>         Environment: Java SE 5.0+
>            Reporter: Michael Wooten
>            Priority: Minor
>             Fix For: 3.1
>         Attachments: commons-lang-event-support.patch
>   Original Estimate: 96h
>  Remaining Estimate: 96h
> I would like to propose some support be added to Lang for basic event handling. This
would be based on the way that PropertyChangeSupport can be used to add and remove listeners
and post events. 
> Add interface EventSupport<L extends EventListener> 
> addListener(L listener)
> The signature for the method that can add a listener of some subtype of EventListener
> removeListener(L listener)
> The signature for the method that can remove a listener of some subtype of EventListener
> Add class AbstractEventSupport implements EventSupport<L>, Iterable<L>
> AbstractEventSupport(Object eventSource)
> Constructs a new AbstractEventSupport object and associates it with the object that will
be used as the source of all events (much like PropertyChangeSupport).
> addListener(L)
> An implementation that adds a listener to an internal collection.
> removeListener(L)
> An implementation that removes a listener from an internal collection.
> iterator()
> Returns an iterator over the attached listeners.
> getSource()
> Returns a reference to the source object of all events.
> The best way to describe this would be to demonstrate an example of how it can be used.
> public class ButtonPressedEventSupport extends AbstractEventSupport<ButtonPressedListener>
>     public ButtonPressedEventSupport(Object source) { super(source); }
>     public void fireButtonPressed(Button button) {
>         ButtonPressedEvent bpe = new ButtonPressedEvent(getSource(), button);
>         for (ButtonPressedListener listener : this)
>         {
>             listener.buttonPressed(bpe);
>         }
>     }
> }
> public class MyWindow implements EventSupport<ButtonPressedListener> {
>      private final ButtonPressedEventSupport buttonPressedEventSupport;
>      public MyWindow { buttonPressedEventSupport = new ButtonPressedEventSupport(this);
>      public void addListener(ButtonPressedListener listener) { buttonPressedEventSupport.addListener(listener);
>      public void removeListener(ButtonPressedListener listener) { buttonPressedEventSupport.removeListener(listener);
>      ...
>     private void onDetectButtonPressed(Button button) {
>         buttonPressedEventSupport.fireButtonPressed(button);
>     }
> }
> I haven't compiled the above code. It's just an example of how these classes could be
used so that you're not constantly rewriting the code and interfaces for adding and removing
listeners, and it provides a fairly easy method of creating methods to fire events.

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