class TsPeriod implements Serializable, Cloneable, IPeriod,
        Comparable<TsPeriod> {

    public Date middle() {
        int ifreq = m_freq.intValue();
        int c = 12 / ifreq;
        int y = getYear(), p = getPosition();
        return new Date(CalendarUtil.getInstance().calcMiddleInMillis(c, y, p));
    }

    public  TsPeriod(final TsFrequency frequency);
    public  TsPeriod(final TsFrequency frequency, final Date date);
    public  TsPeriod(final TsFrequency frequency, final Day day);
      TsPeriod(final TsFrequency frequency, final int id);
    public  TsPeriod(final TsFrequency frequency, final int year,
            final int position);
    public  TsPeriod(final TsFrequency frequency, final TsPeriod p);

}