날짜 관련 클래스들

public static void main(String[] args) {
        Date date = new Date();
        long time = date.getTime();
        System.out.println(date);
        System.out.println(time);
    }
}

1. Tue Jun 06 14:20:32 KST 2023
2. 1686028832024

public static void main(String[] args) throws InterruptedException {
        Date date = new Date();
        long time = date.getTime();
        System.out.println("1. " + date);
        System.out.println("2. " + time);

        Thread.sleep(1000 * 3);
        Date after3Seconds = new Date();
        System.out.println(after3Seconds);

        after3Seconds.setTime(time);
        System.out.println(after3Seconds);
    }
}

Tue Jun 06 14:26:09 KST 2023
Tue Jun 06 14:26:06 KST 2023

public static void main(String[] args) throws InterruptedException {
    Calendar birthDay = new GregorianCalendar(1993, 2, 10);
}

System.out.printf("%s%n", DayOfWeek.SUNDAY.plus(3)); // -> 결과값 : WEDNESDAY

DayOfWeek dow = DayOfWeek.SUNDAY;
Locale locale = Locale.getDefault();
System.out.println(dow.getDisplayName(TextStyle.FULL, locale)); // 일요일
System.out.println(dow.getDisplayName(TextStyle.NARROW, locale)); // 일
System.out.println(dow.getDisplayName(TextStyle.SHORT, locale)); // 일

System.out.printf("%d%n", Month.FEBRUARY.maxLength()); // 결과 : 29

Month month = Month.AUGUST;
Locale locale = Locale.getDefault();
System.out.println(month.getDisplayName(TextStyle.FULL, locale)); //8월
System.out.println(month.getDisplayName(TextStyle.NARROW, locale)); //8월
System.out.println(month.getDisplayName(TextStyle.SHORT, locale)); //8월

LocalDate date = LocalDate.of(2023, Month.JUNE, 6); // 결과 : 2023-06-06
LocalDate nextWed = date.with(TemporalAdjusters.next(DayOfWeek.WEDNESDAY)); // 2023-06-07

DayOfWeek dotw = LocalDate.of(2023,Month.JUNE, 9).getDayOfWeek(); // FRIDAY

LocalDate date = LocalDate.of(2023, Month.JUNE, 9);
TemporalAdjuster adj = TemporalAdjusters.next(DayOfWeek.WEDNESDAY);
LocalDate nextWed = date.with(adj);
System.out.printf("%s의 경우 다음 수요일은 %s.%n", date, nextWed);

2023-06-09의 경우 다음 수요일은 2023-06-14.

YearMonth date = YearMonth.now();
System.out.printf("%s : %d%n", date, date.lengthOfMonth());

YearMonth date2 = YearMonth.of(2023, Month.JULY);
System.out.printf("%s : %d%n", date2, date2.lengthOfMonth());

YearMonth date3 = YearMonth.of(2012, Month.FEBRUARY);
System.out.printf("%s : %d%n", date3, date3.lengthOfMonth());

2023-06 : 30
2023-07 : 31
2012-02 : 29

MonthDay date = MonthDay.of(Month.FEBRUARY, 29);
boolean vaildLeapYear = date.isValidYear(2023);
System.out.println("vaildLeapYear = " + vaildLeapYear);

boolean vaildLeapYear2 = date.isValidYear(2024);
System.out.println("vaildLeapYear2 = " + vaildLeapYear);

vaildLeapYear = false
vaildLeapYear2 = true

boolean  vaildLeapYear2 = Year.of(2024).isLeap(); //true

LocalTime thisSec;

for(;;){
    thisSec = LocalTime.now();
    System.out.printf("%d: %d: %d",thisSec.getHour(), thisSec.getMinute(), thisSec.getSecond());
    System.out.println();
}

6: 53: 3
16: 53: 4
16: 53: 4
16: 53: 4
16: 53: 4
16: 53: 4
16: 53: 4
16: 53: 4
16: 53: 4
16: 53: 4
16: 53: 4
....

System.out.printf("현재: %s%n", LocalDateTime.now() );
System.out.printf("2023년 6월 6일 @ 오전 11시 30분: %s%n", LocalDateTime.of(2023, Month.JUNE, 6, 11, 30) ) ;
System.out.printf("지금 (인스턴트에서): %s%n", LocalDateTime.ofInstant(Instant.now(), ZoneId.systemDefault()) );
System.out.printf("6개월 후: %s%n", LocalDateTime.now().plusMonths(6) );
System.out.printf("6개월 전: %s%n", LocalDateTime.now().minusMonths(6) );

2023년 6월 6일 @ 오전 11시 30분: 2023-06-06T11:30
지금 (인스턴트에서): 2023-06-06T17:02:30.604461
6개월 후: 2023-12-06T17:02:30.604625
6개월 전: 2022-12-06T17:02:30.604837

Set<String> allZones = ZoneId.getAvailableZoneIds();
LocalDateTime dt = LocalDateTime.now();

// 영역 집합을 사용하여 목록을 만들고 정렬한다.
List<String> zoneList = new ArrayList<>(allZones);
Collections.sort(zoneList);

for (String s : zoneList) {
    ZoneId zone = ZoneId.of(s);
    ZonedDateTime zdt = dt.atZone(zone);
    ZoneOffset offset = zdt.getOffset();
    int secondsOfHour = offset.getTotalSeconds() % (60 * 60);
    String out = String.format("%35s %10s%n", zone, offset);

    // 전체 시간 오프셋이 없는 시간대만
    // 표준 출력에 쓴다
    if (secondsOfHour != 0) {
        System.out.printf(out);
    }
}

                   America/St_Johns     -02:30
                      Asia/Calcutta     +05:30
                       Asia/Colombo     +05:30
                         Asia/Kabul     +04:30
                     Asia/Kathmandu     +05:45
                      Asia/Katmandu     +05:45
                       Asia/Kolkata     +05:30
                       Asia/Rangoon     +06:30
                        Asia/Tehran     +04:30
                        Asia/Yangon     +06:30
                 Australia/Adelaide     +09:30
              Australia/Broken_Hill     +09:30
                   Australia/Darwin     +09:30
                    Australia/Eucla     +08:45
                      Australia/LHI     +10:30
                Australia/Lord_Howe     +10:30
                    Australia/North     +09:30
                    Australia/South     +09:30
               Australia/Yancowinna     +09:30
                Canada/Newfoundland     -02:30
                       Indian/Cocos     +06:30
                               Iran     +04:30
                            NZ-CHAT     +12:45
                    Pacific/Chatham     +12:45
                  Pacific/Marquesas     -09:30

DateTimeFormatter format = DateTimeFormatter.ofPattern("MMM d yyyy  hh:mm a");

// Leaving from San Francisco on July 20, 2013, at 7:30 p.m.
LocalDateTime leaving = LocalDateTime.of(2013, Month.JULY, 20, 19, 30);
ZoneId leavingZone = ZoneId.of("America/Los_Angeles");
ZonedDateTime departure = ZonedDateTime.of(leaving, leavingZone);

try {
    String out1 = departure.format(format);
    System.out.printf("LEAVING:  %s (%s)%n", out1, leavingZone);
} catch (DateTimeException exc) {
    System.out.printf("%s can't be formatted!%n", departure);
    throw exc;
}

// Flight is 10 hours and 50 minutes, or 650 minutes
ZoneId arrivingZone = ZoneId.of("Asia/Tokyo");
ZonedDateTime arrival = departure.withZoneSameInstant(arrivingZone).plusMinutes(650);
try {
    String out2 = arrival.format(format);
    System.out.printf("ARRIVING: %s (%s)%n", out2, arrivingZone);
} catch (DateTimeException exc) {
    System.out.printf("%s can't be formatted!%n", arrival);
    throw exc;
}

if (arrivingZone.getRules().isDaylightSavings(arrival.toInstant()))
    System.out.printf("  (%s daylight saving time will be in effect.)%n", arrivingZone);
else
    System.out.printf("  (%s standard time will be in effect.)%n", arrivingZone);

LEAVING:  7월 20 2013  07:30 오후 (America/Los_Angeles)
ARRIVING: 7월 21 2013  10:20 오후 (Asia/Tokyo)
  (Asia/Tokyo standard time will be in effect.)

// 2013년 7월의 마지막 목요일을 찾습니다.
LocalDateTime localDate = LocalDateTime.of(2013, Month.JULY, 20, 19, 30);
ZoneOffset 오프셋 = ZoneOffset.of("-08:00");
OffsetDateTime offsetDate = OffsetDateTime.of(localDate, offset);
OffsetDateTime lastThursday =
offsetDate.with(TemporalAdjusters.lastInMonth(DayOfWeek.THURSDAY));
System.out.printf("2013년 7월 마지막 목요일은 %s일 입니다.", lastThursday.getDayOfMonth())

2013년 7월 마지막 목요일은 25일 입니다.