atom.app.EventBus Maven / Gradle / Ivy
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package atom.app;
import java.io.Serializable;
import java.util.ArrayList;
import java.util.EventObject;
import java.util.HashMap;
import java.util.List;
import java.util.Map;
/**
* Dispatches {@link EventObject}s to interested parties.
*
* Eases decoupling by allowing objects to interact without having direct
* dependencies upon one another, and without requiring event sources to deal
* with maintaining handler lists.
*
* @author Serge Voloshyn
* @version 1.0 10/15/13
*/
public final class EventBus implements Serializable {
/**
* Use serialVersionUID from JDK 1.0.2 for interoperability.
*/
private static final long serialVersionUID = 5446316810559497140L;
/**
* Event handlers map.
*/
private final Map,
List>> handlers = new HashMap<>();
/**
* Register event handler for corresponding event.
*
* @param event event class
* @param handler corresponding event handler
* @param event class type
* @return the handler registration, can be stored in order to remove the
* handler later
*/
public HandlerRegistration addHandler(
final Class event, final EventHandler handler) {
synchronized (handlers) {
final List> list;
if (handlers.containsKey(event)) {
list = handlers.get(event);
} else {
list = new ArrayList<>();
handlers.put(event, list);
}
list.add(handler);
return new HandlerRegistration(list, handler);
}
}
/**
* Fire event to all registered handlers within the registry.
*
* @param event event to be fired
* @param event type
*/
@SuppressWarnings("unchecked")
public void fireEvent(final E event) {
synchronized (handlers) {
final List> list
= handlers.get(event.getClass());
if (list == null) {
return;
}
for (final EventHandler handler : list) {
((EventHandler) handler).handle(event);
}
}
}
/**
* Registration objects returned when an event handler is bound (e.g. via
* {@link EventBus#addHandler}), used to de-register.
*/
public static final class HandlerRegistration implements Serializable {
/**
* Use serialVersionUID from JDK 1.0.2 for interoperability.
*/
private static final long serialVersionUID = 5446316810559497140L;
/**
* Corresponding handler's registry.
*/
private final List> registry;
/**
* Wrapped handler.
*/
private final EventHandler handler;
/**
* Default hidden constructor.
*
* @param aRegistry a corresponding handler's registry
* @param aHandler responsible handler
*/
private HandlerRegistration(final List> aRegistry,
final EventHandler aHandler) {
registry = aRegistry;
handler = aHandler;
}
/**
* Deregisters the handler associated with this registration object if
* the handler is still attached to the event source. If the handler
* is no longer attached to the event source, this is a no-op.
*/
public void removeHandler() {
if (registry != null && handler != null) {
registry.remove(handler);
}
}
}
}