Extend this class to create a DropTargetEvent listener and override the methods for the events of interest. (If you implement the DropTargetListener interface, you have to define all of the methods in it. This abstract class defines a null implementation for every method except drop(DropTargetDropEvent), so you only have to define methods for events you care about.) You must provide an implementation for at least drop(DropTargetDropEvent). 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.
Create a listener object using the extended class and then register it with a DropTarget. When the drag enters, moves over, or exits the operable part of the drop site for that DropTarget, when the drop action changes, and when the drop occurs, the relevant method in the listener object is invoked, and the DropTargetEvent is passed to it.
The operable part of the drop site for the DropTarget is the part of the associated Component's geometry that is not obscured by an overlapping top-level window or by another Component higher in the Z-order that has an associated active DropTarget.
During the drag, the data associated with the current drag operation can be retrieved by calling getTransferable() on DropTargetDragEvent instances passed to the listener's methods.
Note that getTransferable() on the DropTargetDragEvent instance should only be called within the respective listener's method and all the necessary data should be retrieved from the returned Transferable before that method returns.
@see DropTargetEvent
@see DropTargetListener
@author David Mendenhall
@since 1.4
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