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Java 8 Features > Stream API > Date and Time API

Date and Time API

Author: Venkata Sudhakar

Java 8 introduced a completely new Date and Time API in the java.time package to replace the old java.util.Date and java.util.Calendar which were mutable, not thread-safe, and poorly designed. The new API is immutable, thread-safe, and follows the ISO-8601 calendar system.

Key Classes:

1. LocalDate - Represents a date (year, month, day) without time.

2. LocalTime - Represents a time (hours, minutes, seconds) without date.

3. LocalDateTime - Represents a date-time without timezone.

4. ZonedDateTime - Represents a date-time with timezone.

5. Duration and Period - Represent amounts of time.

The below example shows how to use the Java 8 Date and Time API.

import java.time.*;
import java.time.format.DateTimeFormatter;
import java.time.temporal.ChronoUnit;

public class DateTimeAPIExample {
    public static void main(String[] args) {
        // 1. LocalDate - date only
        LocalDate today = LocalDate.now();
        LocalDate birthday = LocalDate.of(1990, Month.MARCH, 15);
        System.out.println("Today: " + today);
        System.out.println("Birthday: " + birthday);
        System.out.println("Is leap year: " + today.isLeapYear());

// 2. LocalTime - time only
        LocalTime now = LocalTime.now();
        LocalTime meeting = LocalTime.of(14, 30, 0);
        System.out.println("\nCurrent time: " + now);
        System.out.println("Meeting at: " + meeting);

// 3. LocalDateTime - date and time
        LocalDateTime dateTime = LocalDateTime.now();
        System.out.println("\nDateTime: " + dateTime);

// 4. Date arithmetic
        LocalDate nextWeek = today.plusDays(7);
        LocalDate lastMonth = today.minusMonths(1);
        System.out.println("\nNext week: " + nextWeek);
        System.out.println("Last month: " + lastMonth);

// 5. Period - difference between dates
        Period age = Period.between(birthday, today);
        System.out.println("\nAge: " + age.getYears() + " years, " + age.getMonths() + " months");

// 6. Duration - difference between times
        Duration duration = Duration.between(meeting, LocalTime.of(16, 0));
        System.out.println("Duration of meeting: " + duration.toMinutes() + " minutes");

// 7. Formatting
        DateTimeFormatter formatter = DateTimeFormatter.ofPattern("dd/MM/yyyy HH:mm");
        String formatted = dateTime.format(formatter);
        System.out.println("\nFormatted: " + formatted);

// 8. Parsing
        LocalDate parsed = LocalDate.parse("25/12/2024", DateTimeFormatter.ofPattern("dd/MM/yyyy"));
        System.out.println("Parsed: " + parsed);

// 9. ZonedDateTime
        ZonedDateTime london = ZonedDateTime.now(ZoneId.of("Europe/London"));
        ZonedDateTime tokyo = ZonedDateTime.now(ZoneId.of("Asia/Tokyo"));
        System.out.println("\nLondon: " + london.format(DateTimeFormatter.ofPattern("HH:mm z")));
        System.out.println("Tokyo: " + tokyo.format(DateTimeFormatter.ofPattern("HH:mm z")));
    }
}

It gives the following output,

Today: 2024-01-15
Birthday: 1990-03-15
Is leap year: true

Current time: 10:30:45.123
Meeting at: 14:30

DateTime: 2024-01-15T10:30:45.123

Next week: 2024-01-22
Last month: 2023-12-15

Age: 33 years, 10 months
Duration of meeting: 90 minutes

Formatted: 15/01/2024 10:30
Parsed: 2024-12-25

London: 10:30 GMT
Tokyo: 19:30 JST

New API vs Old API:

Immutable - All operations return new objects; originals are never modified.

Clear separation - Separate classes for date-only, time-only, datetime, and timezone-aware datetime.

No more null checks - Methods like now(), of(), parse() have clear semantics.

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