java使用Calendar類計算某日期所在季度的開始日期，結束日期

public static Date getSeasonStartDate (Date date) {
    Calendar calendar = Calendar.getInstance();
    calendar.setTime(date);
    int month = calendar.get(Calendar.MONTH);
    calendar.set(Calendar.MONTH, month / 3 * 3);
    calendar.set(Calendar.DATE, 1);
    return calendar.getTime();
}

public static Date getSeasonEndDate (Date date) {
    Calendar calendar = Calendar.getInstance();
    calendar.setTime(date);
    int month = calendar.get(Calendar.MONTH);
    calendar.set(Calendar.MONTH, (month + 3) / 3 * 3);
    calendar.set(Calendar.DATE, 1);
    return new Date(calendar.getTime().getTime() - 24 * 60 * 60 *1000);
}