Error message using Drag And Drop

Question

I receive the following error when trying to use a customized drag implementation on a JList. I can't find any reference to DataTransferer and the like, so I don't know where to look for the problem. Any help would be much appreciated.
java.lang.NullPointerException
at sun.awt.datatransfer.DataTransferer.getFormatsForFlavors(DataTransfer
er.java:708)
at sun.awt.windows.WDataTransferer.getFormatsForFlavors(WDataTransferer.
java:127)
at sun.awt.datatransfer.DataTransferer.getFormatsForTransferable(DataTra
nsferer.java:687)
at sun.awt.dnd.SunDragSourceContextPeer.startDrag(SunDragSourceContextPe
er.java:101)
at java.awt.dnd.DragSource.startDrag(DragSource.java:305)
at java.awt.dnd.DragSource.startDrag(DragSource.java:402)
at java.awt.dnd.DragGestureEvent.startDrag(DragGestureEvent.java:221)

Answer 1

Here is the code that I use for drag and drop between 2 Jlist's. It has always worked for me. You may have to tweek it a little to work for you. For instance I don't have it removing the item from the original lst when it is dragged to the new list. Anyway hope this helps you out.
public static class                     DList extends JList implements DropTargetListener{
        private DropTarget dt;
          DList() {
               this.setDragEnabled(true);
                        dt = new DropTarget(this, this);
        public void dragEnter(DropTargetDragEvent event) {        }
        public void dragExit(DropTargetEvent event) {        }
        public void dragOver(DropTargetDragEvent event) {        }
        public void drop(DropTargetDropEvent event) {
            try {
            Transferable transferable = event.getTransferable();
                if (transferable.isDataFlavorSupported(DataFlavor.stringFlavor)) {
                    event.acceptDrop(DnDConstants.ACTION_COPY);
                      String s = (String)transferable.getTransferData(DataFlavor.stringFlavor);
                      addElement(s);
                    event.getDropTargetContext().dropComplete(true);
                else {
                    event.rejectDrop();
            catch (IOException exception) {
                exception.printStackTrace();
                System.err.println("Exception" + exception.getMessage());
                event.rejectDrop();
            catch (UnsupportedFlavorException ufException) {
                ufException.printStackTrace();
                System.err.println("Exception" + ufException.getMessage());
                event.rejectDrop();
        public void dropActionChanged(DropTargetDragEvent event) {        }
        public void addElement(Object s) {
            ((DefaultListModel)getModel()).addElement(s.toString());
    } //End DList class