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Nifty GUI is a Java Library that supports the building of interactive user interfaces for games or similar applications. It utilizes OpenGL for rendering and it can be easily integrated into many rendering systems. The configuration of the GUI is stored in xml files with little supporting Java code. In short Nifty helps you to layout stuff, display it in a cool way and interact with it :)

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package org.bushe.swing.event.annotation;

import java.lang.annotation.ElementType;
import java.lang.annotation.Retention;
import java.lang.annotation.RetentionPolicy;
import java.lang.annotation.Target;

import org.bushe.swing.event.EventService;
import org.bushe.swing.event.EventServiceLocator;
import org.bushe.swing.event.ThreadSafeEventService;

/**
 * An Annotation for subscribing to EventService Events.
 * 
 * This annotation simplifies much of the repetitive boilerplate used for subscribing to EventService Events.
 * 

 * Instead of this:
 * 
 * public class MyAppController implements EventSubscriber {
 *   public MyAppController {
 *      EventBus.subscribe(AppClosingEvent.class, this);
 *   }
 *   public void onEvent(EventServiceEvent event) {
 *      AppClosingEvent appClosingEvent = (AppClosingEvent)event;
 *      //do something
 *   }
 * }
 * 
 * You can do this:
 *  * public class MyAppController {  //no interface necessary
 *   public MyAppController {
 *       AnnotationProcessor.process(this);//if not using AOP
 *   }
 *   @EventSubscriber
 *   public void onAppClosingEvent(AppClosingEvent appClosingEvent) {//Use your own method name with typesafety
 *      //do something
 *   }
 * }
 * 
 * 
 * That's pretty good, but when the controller does more, annotations are even nicer.
 * 
 * public class MyAppController implements EventSubscriber {
 *   public MyAppController {
 *      EventBus.subscribe(AppStartingEvent.class, this);
 *      EventBus.subscribe(AppClosingEvent.class, this);
 *   }
 *   public void onEvent(EventServiceEvent event) {
 *      //wicked bad pattern, but we have to this
 *      //...or create multiple subscriber classes and hold instances of them fields, which is even more verbose...
 *      if (event instanceof AppStartingEvent) {
 *         onAppStartingEvent((AppStartingEvent)event);
 *      } else (event instanceof AppClosingEvent) {
 *         onAppStartingEvent((AppClosingEvent)event);
 *      }
 *
 *   }
 *
 *   public void onAppStartingEvent(AppStartingEvent appStartingEvent) {
 *      //do something
 *   }
 *
 *   public void onAppClosingEvent(AppClosingEvent appClosingEvent) {
 *      //do something
 *   }
 * }
 * 
 * You can do this:
 *  * public class MyAppController {
 *   public MyAppController {
 *       AnnotationProcessor.process(this);//this line can be avoided with a compile-time tool or an Aspect
 *   }
 *   @EventSubscriber(eventClass=AppStartingEvent.class)
 *   public void onAppStartingEvent(AppStartingEvent appStartingEvent) {
 *      //do something
 *   }
 *   @EventSubscriber(eventClass=AppAppClosingEvent.class)
 *   public void onAppClosingEvent(AppClosingEvent appClosingEvent) {
 *      //do something
 *   }
 * }
 * 
 * Brief, clear, and easy.
 */
@Retention(RetentionPolicy.RUNTIME)
@Target(ElementType.METHOD)
public @interface EventSubscriber {
   /** The class to subscribe to, if not specified, a subscription is created for the type of the method parameter. */
   Class eventClass() default UseTheClassOfTheAnnotatedMethodsParameter.class;

   /** Determines the order in which this subscriber is called, default is FIFO.*/
   int priority() default 0;

   /** Whether or not to subscribe to the exact class or a class hierarchy, defaults to class hierarchy (false). */
   boolean exact() default false;

   /** Whether to subscribe weakly or strongly. */
   ReferenceStrength referenceStrength() default ReferenceStrength.WEAK;

   /** The event service to subscribe to, default to the EventServiceLocator.SERVICE_NAME_EVENT_BUS. */
   String eventServiceName() default EventServiceLocator.SERVICE_NAME_EVENT_BUS;

   /**
    * Whether or not to autocreate the event service if it doesn't exist on subscription, default is true. If the
    * service needs to be created, it must have a default constructor.
    */
   Class autoCreateEventServiceClass() default ThreadSafeEventService.class;
}