difference of lenght - JTextField/date : I have an error type difference of lenght.
Why?       
 {private void txtMoisActionPerformed(ActionEvent e) {

        java.util.Date date1 = jDateChooserDateDebut.getDate();
        java.util.Date date2 = jDateChooserDateFin.getDate();
        long CONST_DURATION_OF_DAY = 1000l * 60 * 60 * 24;
 
        long diff = Math.abs(date2.getTime() - date1.getTime());
        long numberOfMonths = diff/CONST_DURATION_OF_DAY;
        txtMois.setText() = this.numberOfMonts;
        affiche ("txtMois" + numberOfMonths);
    }