🏷 Date & Time
5 patterns
Topic: Date & Time
All Java patterns related to Date & Time — java.evolved
Date/Time
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+
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Date/Time
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+
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Date/Time
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+
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Date/Time
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+
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Date/Time
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+
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