public static Date dateReservedYear000(Calendar calendar) {
        calendar.set(Calendar.MONTH, Calendar.JANUARY);
        calendar.set(Calendar.DAY_OF_MONTH, 1);

        return dateReservedDay000(calendar);
    }
public static Date dateReservedYear000 ( Calendar calendar ) { calendar . set ( Calendar . MONTH , Calendar . JANUARY ) ; calendar . set ( Calendar . DAY_OF_MONTH , 1 ) ; return dateReservedDay000 ( calendar ) ; }
将一个日期的月,日,时,分,秒,毫秒调整为最小值

@param calendar 一个日期
@return 被转化后的日期
@see #dateReservedYear000(Date)