java swing jtextfield modifiying input

To make simple autocorrections in an JTextField, receiving textinput, I
tried to change the text after caretlistener events. But I only get
exceptions

pf, touched: - 0 - 0
Exception in thread "AWT-EventQueue-0" java.lang.IllegalStateException:
Attempt
to mutate in notification
....

main creates a frame with
        JFrame f = new JFrame ("Test");
        Container inhalt = f.getContentPane();

         PhraseField pf = new PhraseField (30);
         inhalt.add (pf [i]);
         pf.addActionListener (new TxtFldAct ());
         pf.addCaretListener (new TxtFldCar ());
         f.setDefaultCloseOperation (JFrame.DISPOSE_ON_CLOSE);
         f.setSize(700,500);
         f.setVisible(true);

and the Listeners try to modify the textField

public class TxtFldCar implements CaretListener
{
    public void caretUpdate (CaretEvent e)
    {
        PhraseField tf = (PhraseField) e.getSource();
        tf.touched ();
    }
}

via the used subclass of JTextField

public class PhraseField extends JTextField
{
    public PhraseField (int columns) { this ("", columns); }
    public PhraseField (String text, int columns)
    {
        super (text, columns);
        this.constant = true;
        this.value = "";
    }
    public void touched ()
    {
        this.setText ("some corrected String"); }
    }
}

Is this the right solution and if so what is my error?

If this is not a good solution, what is a besser one?