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🏷 Date & Time 5 patterns

Topic: Date & Time

All Java patterns related to Date & Time — java.evolved

java.time API basics

Old // Mutable, confusing, zero-indexed months Calendar cal = Calendar.getInstance(); cal.set(2025, 0, 15); // January = 0! Date date = cal.getTime(); // not thread-safe

Modern LocalDate date = LocalDate.of( 2025, Month.JANUARY, 15); LocalTime time = LocalTime.of(14, 30); Instant now = Instant.now(); // immutable, thread-safe

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JDK 8+ learn more →

Duration and Period

Old // How many days between two dates? long diff = date2.getTime() - date1.getTime(); long days = diff / (1000 * 60 * 60 * 24); // ignores DST, leap seconds

Modern long days = ChronoUnit.DAYS .between(date1, date2); Period period = Period.between( date1, date2); Duration elapsed = Duration.between( time1, time2);

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JDK 8+ learn more →

Date formatting

Old // Not thread-safe! SimpleDateFormat sdf = new SimpleDateFormat("yyyy-MM-dd"); String formatted = sdf.format(date); // Must synchronize for concurrent use

Modern DateTimeFormatter fmt = DateTimeFormatter.ofPattern( "uuuu-MM-dd"); String formatted = LocalDate.now().format(fmt); // Thread-safe, immutable

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JDK 8+ learn more →

Instant with nanosecond precision

Old // Millisecond precision only long millis = System.currentTimeMillis(); // 1708012345678

Modern // Microsecond/nanosecond precision Instant now = Instant.now(); // 2025-02-15T20:12:25.678901234Z long nanos = now.getNano();

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JDK 9+ learn more →

Locale constructors to Locale.of()

Old Locale brazilianPortuguese = new Locale("pt", "BR");

Modern Locale brazilianPortuguese = Locale.of("pt", "BR");

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JDK 19+ learn more →