JDK8/Java8源码在线阅读

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 * particular file as subject to the "Classpath" exception as provided
 * by Oracle in the LICENSE file that accompanied this code.
 *
 * This code is distributed in the hope that it will be useful, but WITHOUT
 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
 * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
 * version 2 for more details (a copy is included in the LICENSE file that
 * accompanied this code).
 *
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 * 2 along with this work; if not, write to the Free Software Foundation,
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package java.awt.dnd;

/**
 * An abstract adapter class for receiving drop target events. The methods in
 * this class are empty. This class exists only as a convenience for creating
 * listener objects.
 * <p>
 * Extend this class to create a <code>DropTargetEvent</code> listener
 * and override the methods for the events of interest. (If you implement the
 * <code>DropTargetListener</code> interface, you have to define all of
 * the methods in it. This abstract class defines a null implementation for
 * every method except <code>drop(DropTargetDropEvent)</code>, so you only have
 * to define methods for events you care about.) You must provide an
 * implementation for at least <code>drop(DropTargetDropEvent)</code>. This
 * method cannot have a null implementation because its specification requires
 * that you either accept or reject the drop, and, if accepted, indicate
 * whether the drop was successful.
 * <p>
 * Create a listener object using the extended class and then register it with
 * a <code>DropTarget</code>. When the drag enters, moves over, or exits
 * the operable part of the drop site for that <code>DropTarget</code>, when
 * the drop action changes, and when the drop occurs, the relevant method in
 * the listener object is invoked, and the <code>DropTargetEvent</code> is
 * passed to it.
 * <p>
 * The operable part of the drop site for the <code>DropTarget</code> is
 * the part of the associated <code>Component</code>'s geometry that is not
 * obscured by an overlapping top-level window or by another
 * <code>Component</code> higher in the Z-order that has an associated active
 * <code>DropTarget</code>.
 * <p>
 * During the drag, the data associated with the current drag operation can be
 * retrieved by calling <code>getTransferable()</code> on
 * <code>DropTargetDragEvent</code> instances passed to the listener's
 * methods.
 * <p>
 * Note that <code>getTransferable()</code> on the
 * <code>DropTargetDragEvent</code> instance should only be called within the
 * respective listener's method and all the necessary data should be retrieved
 * from the returned <code>Transferable</code> before that method returns.
 *
 * @see DropTargetEvent
 * @see DropTargetListener
 *
 * @author David Mendenhall
 * @since 1.4
 */
public abstract class DropTargetAdapter implements DropTargetListener {

    /**
     * Called while a drag operation is ongoing, when the mouse pointer enters
     * the operable part of the drop site for the <code>DropTarget</code>
     * registered with this listener.
     *
     * @param dtde the <code>DropTargetDragEvent</code>
     */
    public void dragEnter(DropTargetDragEvent dtde) {}

    /**
     * Called when a drag operation is ongoing, while the mouse pointer is still
     * over the operable part of the drop site for the <code>DropTarget</code>
     * registered with this listener.
     *
     * @param dtde the <code>DropTargetDragEvent</code>
     */
    public void dragOver(DropTargetDragEvent dtde) {}

    /**
     * Called if the user has modified

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