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SciJava Common is a shared library for SciJava software. It provides a plugin framework, with an extensible mechanism for service discovery, backed by its own annotation processor, so that plugins can be loaded dynamically. It is used by downstream projects in the SciJava ecosystem, such as ImageJ and SCIFIO.

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/*
 * #%L
 * SciJava Common shared library for SciJava software.
 * %%
 * Copyright (C) 2009 - 2017 Board of Regents of the University of
 * Wisconsin-Madison, Broad Institute of MIT and Harvard, Max Planck
 * Institute of Molecular Cell Biology and Genetics, University of
 * Konstanz, and KNIME GmbH.
 * %%
 * 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.service;

import org.scijava.Disposable;
import org.scijava.Initializable;
import org.scijava.event.EventService;
import org.scijava.plugin.Plugin;
import org.scijava.plugin.RichPlugin;

/**
 * A SciJava service, for a particular area of functionality.
 * 
 * Services discoverable at runtime must implement this interface and be
 * annotated with @{@link Plugin} with attribute {@link Plugin#type()} =
 * {@link Service}.class. While it possible to create a service merely by
 * implementing this interface, it is encouraged to instead extend
 * {@link AbstractService}, for convenience.
 * 
 * 
 * @author Curtis Rueden
 * @see Plugin
 */
public interface Service extends RichPlugin, Initializable, Disposable {

	/**
	 * Registers the service's event handler methods.
	 * 
	 * NB: This method is not intended to be called directly. It is called by
	 * the service framework itself (specifically by the {@link ServiceHelper})
	 * when initializing the service. It should not be called a second time.
	 * 
	 */
	default void registerEventHandlers() {
		// TODO: Consider removing this method in scijava-common 3.0.0.
		// Instead, the ServiceHelper could just invoke the lines below directly,
		// and there would be one less boilerplate Service method to implement.
		final EventService eventService = context().getService(EventService.class);
		if (eventService != null) eventService.subscribe(this);
	}

	// -- Initializable methods --

	/**
	 * Performs any needed initialization when the service is first loaded.
	 * 
	 * NB: This method is not intended to be called directly. It is called by
	 * the service framework itself (specifically by the {@link ServiceHelper})
	 * when initializing the service. It should not be called a second time.
	 * 
	 */
	@Override
	default void initialize() {
		// NB: Do nothing by default.
	}
}