net.sf.mmm.util.event.api

Interface EventBus

All Known Implementing Classes:

AbstractEventBus, EventBusImpl

@ComponentSpecification
public interface EventBus

This is the interface for an event bus. An event bus is a central place for sending, listening to and receiving Events. The EventBus allows to communicate between loosely coupled components in a smart and efficient way:

• A component sending events only needs to know the EventBus but not the receivers of the events.
• A component receiving events only needs to know the EventBus but not the sender of the events.

This way components can communicate via Events without compile time dependency between them. All they need to see is the EventBus and the Event itself.
This interface exists only for the high abstraction needed for mmm-client. If you want to write a portable client application that can run in different environments (GWT, JavaFx, etc.) then you should use this simplified but normalized API. Otherwise you may want to use an external event bus implementation directly such as guava event bus.
NOTE:
The loose coupling makes flows less easy to see, understand and debug. You should only consider this approach for components that should be decoupled by design. Do not get confused by the beauty of the event-bus pattern and avoid using it where straight method calls should be preferred.
E.g. if you have a user-interface with a navigation sub-dialog and various other dialogs they should communicate via EventBus to update their views accordingly. However, a business component responsible to read and write addresses may get the requirement that in case of a change of an address some logic from the domain of another component should be invoked and that might even reject the change. In the latter case EventBus is the wrong choice.

Since:

5.0.0

Author:

Joerg Hohwiller (hohwille at users.sourceforge.net)

Method Summary

Modifier and Type	Method and Description
<E> void	addListener(Class<E> eventType, EventListener<E> listener) This method registers a listener that is interested in Events.
boolean	removeListener(EventListener<?> listener) This method removes a listener.
<E> void	sendEvent(E event) This method sends an event to all registered listeners.

Method Detail

sendEvent

<E> void sendEvent(E event)

This method sends an event to all registered listeners.

Type Parameters:

E - is the generic type of the Event to send. May be any Object such as a String. However in most cases it is recommended to create real Event classes.

Parameters:

event - is the event to send. May be any Object such as a String. However in most cases it is recommended to create real Event classes.

addListener

<E> void addListener(Class<E> eventType,
                     EventListener<E> listener)

This method registers a listener that is interested in Events.

Type Parameters:

E - is the generic type of the Events to listen to. May be any Object such as a String. However in most cases it is recommended to create real Event classes.

Parameters:

eventType - is the type of the Events to listen to (including all derived types). In limited environments such as GWT, interfaces might not be supported.

listener - is the listener to add.

removeListener

boolean removeListener(EventListener<?> listener)

This method removes a listener. If the listener was not registered before this method will have no effect.

Parameters:

listener - is the listener to remove.

Returns:

true if the given listener has successfully been removed, false if the listener was NOT registered.