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   25   
   26   package java.awt.dnd;
   27   
   28   import java.util.EventListener;
   29   
   30   import java.awt.dnd.DropTargetDragEvent;
   31   import java.awt.dnd.DropTargetDropEvent;
   32   
   33   /**
   34    * The <code>DropTargetListener</code> interface
   35    * is the callback interface used by the
   36    * <code>DropTarget</code> class to provide
   37    * notification of DnD operations that involve
   38    * the subject <code>DropTarget</code>. Methods of
   39    * this interface may be implemented to provide
   40    * "drag under" visual feedback to the user throughout
   41    * the Drag and Drop operation.
   42    * <p>
   43    * Create a listener object by implementing the interface and then register it
   44    * with a <code>DropTarget</code>. When the drag enters, moves over, or exits
   45    * the operable part of the drop site for that <code>DropTarget</code>, when
   46    * the drop action changes, and when the drop occurs, the relevant method in
   47    * the listener object is invoked, and the <code>DropTargetEvent</code> is
   48    * passed to it.
   49    * <p>
   50    * The operable part of the drop site for the <code>DropTarget</code> is
   51    * the part of the associated <code>Component</code>'s geometry that is not
   52    * obscured by an overlapping top-level window or by another
   53    * <code>Component</code> higher in the Z-order that has an associated active
   54    * <code>DropTarget</code>.
   55    * <p>
   56    * During the drag, the data associated with the current drag operation can be
   57    * retrieved by calling <code>getTransferable()</code> on
   58    * <code>DropTargetDragEvent</code> instances passed to the listener's
   59    * methods.
   60    * <p>
   61    * Note that <code>getTransferable()</code> on the
   62    * <code>DropTargetDragEvent</code> instance should only be called within the
   63    * respective listener's method and all the necessary data should be retrieved
   64    * from the returned <code>Transferable</code> before that method returns.
   65    *
   66    * @since 1.2
   67    */
   68   
   69   public interface DropTargetListener extends EventListener {
   70   
   71       /**
   72        * Called while a drag operation is ongoing, when the mouse pointer enters
   73        * the operable part of the drop site for the <code>DropTarget</code>
   74        * registered with this listener.
   75        *
   76        * @param dtde the <code>DropTargetDragEvent</code>
   77        */
   78   
   79       void dragEnter(DropTargetDragEvent dtde);
   80   
   81       /**
   82        * Called when a drag operation is ongoing, while the mouse pointer is still
   83        * over the operable part of the drop site for the <code>DropTarget</code>
   84        * registered with this listener.
   85        *
   86        * @param dtde the <code>DropTargetDragEvent</code>
   87        */
   88   
   89       void dragOver(DropTargetDragEvent dtde);
   90   
   91       /**
   92        * Called if the user has modified
   93        * the current drop gesture.
   94        * <P>
   95        * @param dtde the <code>DropTargetDragEvent</code>
   96        */
   97   
   98       void dropActionChanged(DropTargetDragEvent dtde);
   99   
  100       /**
  101        * Called while a drag operation is ongoing, when the mouse pointer has
  102        * exited the operable part of the drop site for the
  103        * <code>DropTarget</code> registered with this listener.
  104        *
  105        * @param dte the <code>DropTargetEvent</code>
  106        */
  107   
  108       void dragExit(DropTargetEvent dte);
  109   
  110       /**
  111        * Called when the drag operation has terminated with a drop on
  112        * the operable part of the drop site for the <code>DropTarget</code>
  113        * registered with this listener.
  114        * <p>
  115        * This method is responsible for undertaking
  116        * the transfer of the data associated with the
  117        * gesture. The <code>DropTargetDropEvent</code>
  118        * provides a means to obtain a <code>Transferable</code>
  119        * object that represents the data object(s) to
  120        * be transfered.<P>
  121        * From this method, the <code>DropTargetListener</code>
  122        * shall accept or reject the drop via the
  123        * acceptDrop(int dropAction) or rejectDrop() methods of the
  124        * <code>DropTargetDropEvent</code> parameter.
  125        * <P>
  126        * Subsequent to acceptDrop(), but not before,
  127        * <code>DropTargetDropEvent</code>'s getTransferable()
  128        * method may be invoked, and data transfer may be
  129        * performed via the returned <code>Transferable</code>'s
  130        * getTransferData() method.
  131        * <P>
  132        * At the completion of a drop, an implementation
  133        * of this method is required to signal the success/failure
  134        * of the drop by passing an appropriate
  135        * <code>boolean</code> to the <code>DropTargetDropEvent</code>'s
  136        * dropComplete(boolean success) method.
  137        * <P>
  138        * Note: The data transfer should be completed before the call  to the
  139        * <code>DropTargetDropEvent</code>'s dropComplete(boolean success) method.
  140        * After that, a call to the getTransferData() method of the
  141        * <code>Transferable</code> returned by
  142        * <code>DropTargetDropEvent.getTransferable()</code> is guaranteed to
  143        * succeed only if the data transfer is local; that is, only if
  144        * <code>DropTargetDropEvent.isLocalTransfer()</code> returns
  145        * <code>true</code>. Otherwise, the behavior of the call is
  146        * implementation-dependent.
  147        * <P>
  148        * @param dtde the <code>DropTargetDropEvent</code>
  149        */
  150   
  151       void drop(DropTargetDropEvent dtde);
  152   }

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