ToolTipManager.sharedInstance().registerComponent(jgraph);

jgraph.addMouseListener(new MouseAdapter() {
public void mousePressed(MouseEvent e) {
        if (e.getClickCount() == 2) {
            int x = e.getX(), y = e.getY();
                Object cell= jgraph.getFirstCellForLocation(x, y);

                if (cell != null) {
                String lab = jgraph.convertValueToString(cell);
                jgraph.setToolTipText(lab);

                System.out.println(lab);
                 }
            }
    }
  });