LocalDateTime 예제

마지막날 구하기 등등

 

import java.time.*;
import java.time.format.DateTimeFormatter;
import java.time.temporal.TemporalAdjusters;
import java.util.Date;

public class LocalDateTimeExc {
  public static void main(String[] args) {
    final int[] TIME_UNIT = {3600, 60, 1};
    final String[] TIME_NAME = {"시간", "분", "초"};

    LocalDateTime ldt = LocalDateTime.now();

    System.out.println(ldt.getDayOfMonth());
    System.out.println(ldt.getMonth());


    LocalTime lt = LocalTime.now();
    System.out.println(lt);

    LocalDate ld = LocalDate.now();
    System.out.println(ld);

    Date d1 = new Date();
    long time = d1.getTime();

    System.out.println("현재 밀리초 : "+time);

    LocalDateTime ldt1 = LocalDateTime.of(2002, 3, 1, 4, 9, 22);
    LocalDateTime ldt2 = LocalDateTime.of(2002, 3, 2, 1, 3, 2);
    LocalDateTime ldt3 = LocalDateTime.now()
            .with(LocalDateTime.of(
                    2002,3,22,22,33,22
            ));

    System.out.println("getDayOfWeek() "+ldt1.getDayOfWeek());
    System.out.println("getMonth() "+ldt1.getMonth());
    
    LocalDate start = LocalDate.from(ldt1.withDayOfMonth(1));
    System.out.println(ldt1.withDayOfMonth(start.lengthOfMonth()));
    LocalDateTime ldt4 = LocalDate.now().atTime(6, 0);

    ZonedDateTime zdt = ldt1.atZone(ZoneId.of("Asia/Seoul"));
    long millis = zdt.toInstant().toEpochMilli();
    System.out.println("밀리초 with ZoneID: "+millis);

    System.out.println("ldt " + LocalDateTime.now().atZone(ZoneId.systemDefault()).toInstant().toEpochMilli());
    System.out.println("ctm " + System.currentTimeMillis());

    LocalDateTime date = LocalDateTime.of(1977, 1, 1, 0, 0);
    long millisNoZoneId = date.toInstant(ZoneOffset.ofTotalSeconds(0)).toEpochMilli();
    System.out.println("밀리초 without ZoneID: "+millisNoZoneId);

    long difference = (ldt2.toInstant(ZoneOffset.ofTotalSeconds(0)).toEpochMilli() - ldt1.toInstant(ZoneOffset.ofTotalSeconds(0)).toEpochMilli())/1000 ;

    System.out.println("두 시간 간의 차이 나는 초는 "+difference);

    StringBuilder tmp = new StringBuilder();
    for (int i = 0; i < TIME_UNIT.length ; i++) {
      tmp.append(difference / TIME_UNIT[i]).append(TIME_NAME[i]).append(" ");
      difference %= TIME_UNIT[i];
    }
    System.out.println("시 분 초로 변환 하면 "+ tmp.toString().trim());

    // 해당 월의 마지막 날 구하기
    LocalDate monthStart = LocalDate.of(2002, 4, 1);
    LocalDate monthEnd = monthStart.plusDays(monthStart.lengthOfMonth() -1);
    System.out.println("해당 월의 마지막 날 : "+monthEnd.getDayOfMonth());

    LocalDate lastDate = LocalDate.now().with(TemporalAdjusters.lastDayOfMonth());
    String lastDateString = lastDate.format(DateTimeFormatter.ISO_DATE);
    System.out.println(lastDateString); // 2021-06-30
    System.out.println(lastDate.getDayOfMonth());

    LocalDate ld3 = LocalDate.of(2002, 4, 3);
    LocalDate lastdDate1 = ld3.with(TemporalAdjusters.lastDayOfMonth());
    System.out.println("날짜 지정후 마지막 날 구하기"+lastdDate1);

    LocalDateTime ld4 = LocalDateTime.of(2002, 4, 3, 22,3,2);
    LocalDateTime lastdDate2 = ld4.with(TemporalAdjusters.lastDayOfMonth());
    System.out.println("날짜 지정후 마지막 날 구하기"+lastdDate2);

    LocalDate ld1 = LocalDate.now();
    LocalDate lastDay = LocalDate.ofEpochDay(ld1.lengthOfMonth() -1);

    System.out.println(lastDay);

    // =====================================
    LocalDateTime now = LocalDateTime.now();
    System.out.println("Now is " + now);

    LocalDateTime now2 = LocalDateTime.of(LocalDate.now(), LocalTime.now());
    System.out.println("Now is " + now2);

    LocalDateTime y2k = LocalDateTime.parse("1999-12-31T23:59:59.999");
    System.out.println("Y2K is " + y2k);

    LocalDateTime dateOfBirth = LocalDateTime.of(1982, 7, 13, 14, 25, 0);
    System.out.println("My date of birth is " + dateOfBirth);

    LocalDateTime dateOfBirth2 = Year.of(1982).atMonth(7).atDay(13).atTime(14, 25);
    System.out.println("My date of birth is " + dateOfBirth2);

    LocalDateTime nowLdt = LocalDateTime.now(); // 현재시간

    LocalDateTime threeYearsAfter = nowLdt.plusYears(3); // 3년 뒤 - now는 계속 현재시간
    LocalDateTime twoDaysAgo = nowLdt.minusDays(2); // 2일 전
    LocalDateTime twoDaysAndThreeHoursAgo = nowLdt.minusDays(2).minusHours(3); // 2일 3시간 전


  }
}