FocusListener

Question

Hi,
My prob is I got two JTextFields, only one editable. The text supposed to be entered, should only contain positive numbers (which I realize by the use of a Document). Ok so far.
When I tab from that editable JTextField to some other field or, say, put the focus on another widget, the input should be checked (value to big, whatever..) or written to the other JTextField (ineditable). I tried this with an ActionListener, but now it only works on ENTER. How to get that done when I already move the focus away from that field by a TAB?
(I thought about using a FocusListener, well - I'm not setting the focus to somewhere, but removing it from somewhere..???)
public class DlgCustomizeSelection03 extends javax.swing.JDialog {
     private JTextField tfGroupsStart;
     private JTextField tfStartCol;
// init and setting up GUI..
// init ActionListener
          tfGroupsStart.addActionListener( new ActionListener(){
               public void actionPerformed( ActionEvent ae){
                    // check the input and do the following if input is ok
                    tfStartCol.setText( String.valueOf(iVal));
(...)

Answer 1

should only contain positive numbers (which I realize by the use of a Document)...
put the focus on another widget, the input should be checked (value to big, whatever..)perhaps extending the function of the document you mention, to include
checking/disallowing when "value to big, whatever..", might be a better approach