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    1   /*
    2    * Copyright (c) 2001, 2003, Oracle and/or its affiliates. All rights reserved.
    3    * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
    4    *
    5    * This code is free software; you can redistribute it and/or modify it
    6    * under the terms of the GNU General Public License version 2 only, as
    7    * published by the Free Software Foundation.  Oracle designates this
    8    * particular file as subject to the "Classpath" exception as provided
    9    * by Oracle in the LICENSE file that accompanied this code.
   10    *
   11    * This code is distributed in the hope that it will be useful, but WITHOUT
   12    * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
   13    * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
   14    * version 2 for more details (a copy is included in the LICENSE file that
   15    * accompanied this code).
   16    *
   17    * You should have received a copy of the GNU General Public License version
   18    * 2 along with this work; if not, write to the Free Software Foundation,
   19    * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
   20    *
   21    * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
   22    * or visit www.oracle.com if you need additional information or have any
   23    * questions.
   24    */
   25   
   26   package java.awt.dnd;
   27   
   28   /**
   29    * An abstract adapter class for receiving drop target events. The methods in
   30    * this class are empty. This class exists only as a convenience for creating
   31    * listener objects.
   32    * <p>
   33    * Extend this class to create a <code>DropTargetEvent</code> listener
   34    * and override the methods for the events of interest. (If you implement the
   35    * <code>DropTargetListener</code> interface, you have to define all of
   36    * the methods in it. This abstract class defines a null implementation for
   37    * every method except <code>drop(DropTargetDropEvent)</code>, so you only have
   38    * to define methods for events you care about.) You must provide an
   39    * implementation for at least <code>drop(DropTargetDropEvent)</code>. This
   40    * method cannot have a null implementation because its specification requires
   41    * that you either accept or reject the drop, and, if accepted, indicate
   42    * whether the drop was successful.
   43    * <p>
   44    * Create a listener object using the extended class and then register it with
   45    * a <code>DropTarget</code>. When the drag enters, moves over, or exits
   46    * the operable part of the drop site for that <code>DropTarget</code>, when
   47    * the drop action changes, and when the drop occurs, the relevant method in
   48    * the listener object is invoked, and the <code>DropTargetEvent</code> is
   49    * passed to it.
   50    * <p>
   51    * The operable part of the drop site for the <code>DropTarget</code> is
   52    * the part of the associated <code>Component</code>'s geometry that is not
   53    * obscured by an overlapping top-level window or by another
   54    * <code>Component</code> higher in the Z-order that has an associated active
   55    * <code>DropTarget</code>.
   56    * <p>
   57    * During the drag, the data associated with the current drag operation can be
   58    * retrieved by calling <code>getTransferable()</code> on
   59    * <code>DropTargetDragEvent</code> instances passed to the listener's
   60    * methods.
   61    * <p>
   62    * Note that <code>getTransferable()</code> on the
   63    * <code>DropTargetDragEvent</code> instance should only be called within the
   64    * respective listener's method and all the necessary data should be retrieved
   65    * from the returned <code>Transferable</code> before that method returns.
   66    *
   67    * @see DropTargetEvent
   68    * @see DropTargetListener
   69    *
   70    * @author David Mendenhall
   71    * @since 1.4
   72    */
   73   public abstract class DropTargetAdapter implements DropTargetListener {
   74   
   75       /**
   76        * Called while a drag operation is ongoing, when the mouse pointer enters
   77        * the operable part of the drop site for the <code>DropTarget</code>
   78        * registered with this listener.
   79        *
   80        * @param dtde the <code>DropTargetDragEvent</code>
   81        */
   82       public void dragEnter(DropTargetDragEvent dtde) {}
   83   
   84       /**
   85        * Called when a drag operation is ongoing, while the mouse pointer is still
   86        * over the operable part of the drop site for the <code>DropTarget</code>
   87        * registered with this listener.
   88        *
   89        * @param dtde the <code>DropTargetDragEvent</code>
   90        */
   91       public void dragOver(DropTargetDragEvent dtde) {}
   92   
   93       /**
   94        * Called if the user has modified
   95        * the current drop gesture.
   96        *
   97        * @param dtde the <code>DropTargetDragEvent</code>
   98        */
   99       public void dropActionChanged(DropTargetDragEvent dtde) {}
  100   
  101       /**
  102        * Called while a drag operation is ongoing, when the mouse pointer has
  103        * exited the operable part of the drop site for the
  104        * <code>DropTarget</code> registered with this listener.
  105        *
  106        * @param dte the <code>DropTargetEvent</code>
  107        */
  108       public void dragExit(DropTargetEvent dte) {}
  109   }

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