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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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package org.scijava.ui.dnd;

import java.util.List;

import org.scijava.display.Display;
import org.scijava.plugin.HandlerService;
import org.scijava.service.SciJavaService;

/**
 * Interface for service that handles drag and drop events.
 * 
 * @author Curtis Rueden
 */
public interface DragAndDropService extends
	HandlerService>, SciJavaService
{

	/**
	 * Checks whether the given {@link DragAndDropData} can be dropped onto the
	 * specified display. A (data, display) pair is deemed compatible if a
	 * compatible handler exists for them.
	 * 
	 * @see DragAndDropHandler
	 */
	default boolean supports(final DragAndDropData data,
		final Display display)
	{
		return getHandler(data, display) != null;
	}

	/**
	 * Checks whether the given object can be dropped onto the specified display.
	 * An (object, display) pair is deemed compatible if a compatible handler
	 * exists for them.
	 * 
	 * @see DragAndDropHandler
	 */
	default boolean supports(final Object object, final Display display) {
		return getHandler(object, display) != null;
	}

	/**
	 * Performs a drag-and-drop operation in the given display with the specified
	 * {@link DragAndDropData}, using the first available compatible handler.
	 * 
	 * @see DragAndDropHandler
	 * @return true if the drop operation was successful
	 * @throws IllegalArgumentException if the display and/or data object are
	 *           unsupported, or are incompatible with one another.
	 */
	default boolean drop(final DragAndDropData data, final Display display) {
		final DragAndDropHandler handler = getHandler(data, display);
		if (handler == null) return false;
		return handler.dropData(data, display);
	}

	/**
	 * Performs a drag-and-drop operation in the given display with the specified
	 * data object, using the first available compatible handler.
	 * 
	 * @see DragAndDropHandler
	 * @return true if the drop operation was successful
	 * @throws IllegalArgumentException if the display and/or data object are
	 *           unsupported, or are incompatible with one another.
	 */
	default boolean drop(final Object data, final Display display) {
		final DragAndDropHandler handler = getHandler(data, display);
		if (handler == null) return false;
		return handler.dropObject(data, display);
	}

	/**
	 * Gets the drag-and-drop handler which will be used to handle the given
	 * {@link DragAndDropData} dragged onto the specified display.
	 * 
	 * @return The first compatible drag-and-drop handler, or null if none
	 *         available.
	 */
	default DragAndDropHandler getHandler(final DragAndDropData data,
		final Display display)
	{
		for (final DragAndDropHandler handler : getInstances()) {
			if (handler.supportsData(data, display)) return handler;
		}
		return null;
	}

	/**
	 * Gets the drag-and-drop handler which will be used to handle the given
	 * object dragged onto the specified display.
	 * 
	 * @return The first compatible drag-and-drop handler, or null if none
	 *         available.
	 */
	default DragAndDropHandler getHandler(final Object object,
		final Display display)
	{
		for (final DragAndDropHandler handler : getInstances()) {
			if (handler.supportsObject(object, display)) return handler;
		}
		return null;
	}

	// NB: Javadoc overrides.

	// -- SingletonService methods --

	/**
	 * Gets the list of available drag-and-drop handlers, which are used to
	 * perform drag-and-drop operations.
	 */
	@Override
	List> getInstances();

	// -- PTService methods --

	@Override
	@SuppressWarnings({"rawtypes", "unchecked"})
	default Class> getPluginType() {
		return (Class) DragAndDropHandler.class;
	}

	// -- Typed methods --

	@Override
	default Class