org.scijava.event.EventHandler Maven / Gradle / Ivy
Show all versions of scijava-common Show documentation
/*
* #%L
* SciJava Common shared library for SciJava software.
* %%
* Copyright (C) 2009 - 2014 Board of Regents of the University of
* Wisconsin-Madison, Broad Institute of MIT and Harvard, and Max Planck
* Institute of Molecular Cell Biology and Genetics.
* %%
* Redistribution and use in source and binary forms, with or without
* modification, are permitted provided that the following conditions are met:
*
* 1. Redistributions of source code must retain the above copyright notice,
* this list of conditions and the following disclaimer.
* 2. Redistributions in binary form must reproduce the above copyright notice,
* this list of conditions and the following disclaimer in the documentation
* and/or other materials provided with the distribution.
*
* THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
* AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
* IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
* ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDERS OR CONTRIBUTORS BE
* LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
* CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
* SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
* INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
* CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
* ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
* POSSIBILITY OF SUCH DAMAGE.
* #L%
*/
package org.scijava.event;
import java.lang.annotation.ElementType;
import java.lang.annotation.Retention;
import java.lang.annotation.RetentionPolicy;
import java.lang.annotation.Target;
/**
* Annotation identifying an event handler method. This annotation allows a
* class to subscribe to multiple types of events by implementing multiple event
* handling methods and annotating each with @{@link EventHandler}.
*
* Note to developers: This annotation serves exactly the same purpose as
* EventBus's {@link org.bushe.swing.event.annotation.EventSubscriber}
* annotation, recapitulating a subset of the same functionality. We do this to
* avoid third party code depending directly on EventBus. That is, we do not
* wish to require SciJava developers to {@code import org.bushe.swing.event.*}
* or similar. In this way, EventBus is isolated as only a transitive dependency
* of downstream code, rather than a direct dependency. Unfortunately, because
* Java annotation interfaces cannot utilize inheritance, we have to
* recapitulate the functionality rather than extend it (as we are able to do
* with {@link EventSubscriber}).
*
*
* @author Curtis Rueden
* @see EventService
*/
@Retention(RetentionPolicy.RUNTIME)
@Target(ElementType.METHOD)
public @interface EventHandler {
/**
* Unique subscription key. If multiple {@code @EventHandler} annotations
* exist with the same key, only the first to be subscribed will be respected;
* the others will be silently ignored. If no key is specified, the event
* handler is always subscribed.
*
* This feature exists to enable better extensibility of event handling: if
* code exists that handles an event in an undesirable way, that logic can be
* completely intercepted and overridden by writing more code that handles the
* event in a better way, specifying the same key as the original.
*
*/
String key() default "";
}