JavaでCalendarを使って月の最初の日と最後の日を返すプログラム

gistfile1.txt

 // 月初日を返す
    public static Date getFirstDate(Date date) {

        if (date==null) return null;

        Calendar calendar = Calendar.getInstance();
        calendar.setTime(date);
        int first = calendar.getActualMinimum(Calendar.DATE);
        calendar.set(Calendar.DATE, first);

        calendar.set(Calendar.HOUR_OF_DAY, 00);
        calendar.set(Calendar.MINUTE, 00);
        calendar.set(Calendar.SECOND, 00);
        calendar.set(Calendar.MILLISECOND, 000);

        return calendar.getTime();
    }

    // 月末日を返す
    public static Date getLastDate(Date date) {

        if (date==null) return null;

        Calendar calendar = Calendar.getInstance();
        calendar.setTime(date);
        int last = calendar.getActualMaximum(Calendar.DATE);
        calendar.set(Calendar.DATE, last);

        calendar.set(Calendar.HOUR_OF_DAY, 23);
        calendar.set(Calendar.MINUTE, 59);
        calendar.set(Calendar.SECOND, 59);
        calendar.set(Calendar.MILLISECOND, 999);

        return calendar.getTime();
    }