The LocalDateTime Class
The class LocalDateTime allows the date and the time to be combined into one entity, which is useful for representing such concepts as appointments that require both a time and a date. The of() methods in the LocalDateTime class are combinations of the of() methods from the LocalTime and LocalDate classes, taking values of both time and date fields as arguments. The toString() method of this class will format the temporal fields according to the ISO standard (ยง18.6, p. 1134):
uuuu-MM-ddTHH:mm:ss.SSSSSSSSS
The letter T separates the values of the date fields from those of the time fields.
// 2021-04-28T12:15
LocalDateTime dt1 = LocalDateTime.of(2021, 4, 28, 12, 15);
// 2021-08-19T14:00
LocalDateTime dt2 = LocalDateTime.of(2021, Month.AUGUST, 19, 14, 0);
The LocalDateTime class also provides an of() method that combines a LocalDate object and a LocalTime object. The first declaration in the next code snippet combines a date and a time. The static field LocalTime.NOON defines the time at noon. In addition, the LocalTime class provides the instance method atDate(), which takes a date as an argument and returns a LocalDateTime object. The second declaration combines the time at noon with the date referred to by the reference date1. Conversely, the LocalDate class provides the overloaded instance method atTime() to combine a date with a specified time. In the last two declarations, the atTime() method is passed a LocalTime object and values for specific time fields, respectively.
// LocalDate date1 is 1969-07-20.
LocalDateTime dt3 = LocalDateTime.of(date1, LocalTime.NOON); // 1969-07-20T12:00
LocalDateTime dt4 = LocalTime.of(12, 0).atDate(date1); // 1969-07-20T12:00
LocalDateTime dt5 = date1.atTime(LocalTime.NOON); // 1969-07-20T12:00
LocalDateTime dt6 = date1.atTime(12, 0); // 1969-07-20T12:00
As a convenience, each temporal class provides a static method now() that reads the system clock and returns the values for the relevant temporal fields in an instance of the target class.
LocalTime currentTime = LocalTime.now();
LocalDate currentDate = LocalDate.now();
LocalDateTime currentDateTime = LocalDateTime.now();
Example 17.1 includes the different ways to create temporal objects that we have discussed so far.
// LocalTime
LocalDateTime atDate(LocalDate date)
Returns a LocalDateTime that combines this time with the specified date.
// LocalDate
LocalDateTime atTime(LocalTime time)
LocalDateTime atTime(int hour, int minute)
LocalDateTime atTime(int hour, int minute, int second)
LocalDateTime atTime(int hour, int minute, int second, int nanoOfSecond)
LocalDateTime atStartOfDay()
Return a LocalDateTime that combines this date with the specified values for time fields. The second and nanosecond fields are set to zero, if their values are not specified. In the last method, this date is combined with the time at midnight.
// LocalDateTime
ZonedDateTime atZone(ZoneId zone)
Returns a ZonedDateTime by combining this date-time with the specified time zone (p. 1072).
// LocalTime, LocalDate, LocalDateTime, respectively.
static LocalTime now()
static LocalDate now()
static LocalDateTime now()
Each temporal class has this static factory method, which returns either the current time, date, or date-time from the system clock.
Example 17.1 Creating Local Dates and Local Times
import java.time.LocalDate;
import java.time.LocalDateTime;
import java.time.LocalTime;
import java.time.Month;
public class CreatingTemporals {
public static void main(String[] args) {
// Creating a specific time from time-based values:
LocalTime time1 = LocalTime.of(8, 15, 35, 900);// 08:15:35.000000900
LocalTime time2 = LocalTime.of(16, 45); // 16:45
// LocalTime time3 = LocalTime.of(25, 13, 30); // DateTimeException
System.out.println(“Surveillance start time: ” + time1);
System.out.println(“Closing time: ” + time2);
// Creating a specific date from date-based values:
LocalDate date1 = LocalDate.of(1969, 7, 20); // 1969-07-20
LocalDate date2 = LocalDate.of(-3113, Month.AUGUST, 11);// -3113-08-11
// LocalDate date3 = LocalDate.of(2021, 13, 11); // DateTimeException
// LocalDate date4 = LocalDate.of(2021, 2, 29); // DateTimeException
System.out.println(“Date of lunar landing: ” + date1);
System.out.println(“Start Date of Mayan Calendar: ” + date2);
// Creating a specific date-time from date- and time-based values.
// 2021-04-28T12:15
LocalDateTime dt1 = LocalDateTime.of(2021, 4, 28, 12, 15);
// 2021-08-17T14:00
LocalDateTime dt2 = LocalDateTime.of(2021, Month.AUGUST, 17, 14, 0);
System.out.println(“Car service appointment: ” + dt1);
System.out.println(“Hospital appointment: ” + dt2);
// Combining date and time objects.
// 1969-07-20T12:00
LocalDateTime dt3 = LocalDateTime.of(date1, LocalTime.NOON);
LocalDateTime dt4 = LocalTime.of(12, 0).atDate(date1);
LocalDateTime dt5 = date1.atTime(LocalTime.NOON);
LocalDateTime dt6 = date1.atTime(12, 0);
System.out.println(“Factory date-time combo: ” + dt3);
System.out.println(“Time with date combo: ” + dt4);
System.out.println(“Date with time combo: ” + dt5);
System.out.println(“Date with explicit time combo: ” + dt6);
// Current time:
LocalTime currentTime = LocalTime.now();
System.out.println(“Current time: ” + currentTime);
// Current date:
LocalDate currentDate = LocalDate.now();
System.out.println(“Current date: ” + currentDate);
// Current date and time:
LocalDateTime currentDateTime = LocalDateTime.now();
System.out.println(“Current date-time: ” + currentDateTime);
}
}
Possible output from the program:
Click here to view code image Surveillance start time: 08:15:35.000000900
Closing time: 16:45
Date of lunar landing: 1969-07-20
Start Date of Mayan Calendar: -3113-08-11
Car service appointment: 2021-04-28T12:15
Hospital appointment: 2021-08-17T14:00
Factory date-time combo: 1969-07-20T12:00
Time with date combo: 1969-07-20T12:00
Date with time combo: 1969-07-20T12:00
Date with explicit time combo: 1969-07-20T12:00
Current time: 10:55:41.296744
Current date: 2021-03-05
Current date-time: 2021-03-05T10:55:41.299318