public void addMonth(int m) {
    int modM = m > 0 ? m : -m;
    int sign = m > 0 ? 1 : -1;
    Date old = calendar.getTime();
    for (int i = 0; i < modM; i++) {
      calendar.add(Calendar.MONTH, sign);
    }
    firePropertyChange(PROPERTY_NAME_DATE, old, getDate());
    reflectData();

  }
public void addMonth(int m)