DATE, TIME, AND LOCALIZATION
LocalDate and LocalTime Operations (Date-Time API)
Rule: LocalDate/LocalTime/LocalDateTime are immutable - all methods return new instances.
- LocalDate: Date only (year, month, day)
- LocalTime: Time only (hour, minute, second, nanosecond)
- LocalDateTime: Date and time combined
import java.time.*;
// Creating date/time objects
LocalDate today = LocalDate.now(); // Current date
LocalDate birthday = LocalDate.of(2000, 5, 15); // May 15, 2000
LocalTime now = LocalTime.now(); // Current time
LocalTime lunch = LocalTime.of(12, 30); // 12:30 PM
LocalDateTime meeting = LocalDateTime.of(2024, 3, 20, 14, 30); // Mar 20, 2024 at 2:30 PM
// All methods return NEW instances (immutable)
LocalDate tomorrow = today.plusDays(1); // Add 1 day
LocalDate nextMonth = today.plusMonths(1); // Add 1 month
LocalTime later = lunch.plusHours(2); // Add 2 hours
LocalDate earlier = birthday.minusYears(5); // Subtract 5 years
// Original objects unchanged
System.out.println(today); // Still original date
System.out.println(lunch); // Still 12:30
Period and Duration:
// Period - date-based amounts (years, months, days)
Period age = Period.between(birthday, today);
System.out.println("Age: " + age.getYears() + " years");
Period twoWeeks = Period.ofDays(14);
LocalDate vacation = today.plus(twoWeeks);
// Duration - time-based amounts (hours, minutes, seconds)
Duration workDay = Duration.ofHours(8);
LocalTime endWork = LocalTime.of(9, 0).plus(workDay); // 9:00 AM + 8 hours = 5:00 PM
Duration between = Duration.between(lunch, now);
System.out.println("Hours since lunch: " + between.toHours());
💡 Learning Tip: Remember “IMMUTABLE TIME” - LocalDate/Time classes never change, they always return new instances. Period for dates, Duration for time.
Q: If you call birthday.plusYears(10) without assigning the result, does birthday change?
A: No — LocalDate is immutable. The method returns a new LocalDate instance, but birthday remains unchanged.