The listener interface for receiving drag gesture events.
This interface is intended for a drag gesture recognition
implementation. See a specification for DragGestureRecognizer
for details on how to register the listener interface.
Upon recognition of a drag gesture the
DragGestureRecognizer calls this interface's
method and passes a DragGestureEvent.
This method is invoked by the DragGestureRecognizer
when the DragGestureRecognizer detects a platform-dependent
drag initiating gesture. To initiate the drag and drop operation,
if appropriate, startDrag() method on
the DragGestureEvent has to be invoked.
dge - the DragGestureEvent describing
the gesture that has just occurred