libs1DateTimeApi

1package pkg13libs;2 3import java.time.Duration;4import java.time.LocalDate;5import java.time.LocalDateTime;6import java.time.Period;7import java.time.ZoneId;8import java.time.ZonedDateTime;9import java.time.format.DateTimeFormatter;10import java.time.temporal.ChronoUnit;11 12/*13 * libs1DateTimeApi.java14 * ---------------------15 * The modern Date/Time API (java.time, Java 8+) — immutable and thread-safe.16 *17 * DEFINITION:18 *   java.time models dates, times, instants, durations, and zones with clear,19 *   immutable types. It replaces the error-prone java.util.Date/Calendar.20 *21 * KEY POINTS:22 *   - LocalDate/LocalTime/LocalDateTime: no time zone. ZonedDateTime: with zone.23 *   - Instant: a point on the UTC timeline (good for timestamps).24 *   - Period = date-based amount (years/months/days); Duration = time-based.25 *   - All types are immutable: plusDays() returns a NEW object.26 */27public class libs1DateTimeApi {28 29    public static void main(String[] args) {30        LocalDate today = LocalDate.now();31        System.out.println("Today        : " + today);32        System.out.println("In 30 days   : " + today.plusDays(30));33        System.out.println("Day of week  : " + today.getDayOfWeek());34 35        LocalDateTime now = LocalDateTime.now();36        System.out.println("\nNow          : " + now);37        System.out.println("Formatted    : " +38                now.format(DateTimeFormatter.ofPattern("yyyy-MM-dd HH:mm:ss")));39 40        // Time zones41        ZonedDateTime tokyo = now.atZone(ZoneId.systemDefault())42                                 .withZoneSameInstant(ZoneId.of("Asia/Tokyo"));43        System.out.println("\nSame instant in Tokyo: " + tokyo);44 45        // Period (date span) vs Duration (time span)46        LocalDate launch = LocalDate.of(1995, 5, 23);   // Java's public debut47        Period age = Period.between(launch, today);48        System.out.printf("%nJava is %d years, %d months, %d days old%n",49                age.getYears(), age.getMonths(), age.getDays());50        System.out.println("That is " + ChronoUnit.DAYS.between(launch, today) + " days");51 52        Duration meeting = Duration.ofHours(1).plusMinutes(30);53        System.out.println("\nDuration     : " + meeting + " = " + meeting.toMinutes() + " minutes");54 55        // Parsing56        LocalDate parsed = LocalDate.parse("2030-12-25");57        System.out.println("\nParsed date  : " + parsed + " (a " + parsed.getDayOfWeek() + ")");58    }59}