import java.awt.datatransfer.Transferable;

static void listEnableDrag(final JList list, TransferHandler th) {
  if (list.getDragEnabled()) {
    print("List drag already enabled");
    ret;
  }
  list.setDragEnabled(true);
  list.setTransferHandler(th);
  list.addMouseListener(new MouseAdapter {
    @Override
    public void mousePressed(MouseEvent e) {
      if (e.getButton() == 1 && e.getClickCount() == 1)
        list.getTransferHandler().exportAsDrag(list, e, TransferHandler.COPY);
    }
  });
}

Began life as a copy of #1007217