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Date/Time Intermediate

Instant with nanosecond precision

Get timestamps with microsecond or nanosecond precision.

Code Comparison

✕ Java 8

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

✓ Java 9+

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

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Why the modern way wins

🎯

Higher precision

Microsecond/nanosecond vs millisecond timestamps.

📐

Type-safe

Instant carries its precision — no ambiguous longs.

🌐

UTC-based

Instant is always in UTC — no timezone confusion.

Old Approach

Milliseconds

Modern Approach

Nanoseconds

Since JDK

Difficulty

Intermediate

JDK Support

Instant with nanosecond precision

Available

Widely available since JDK 9 (Sept 2017)

How it works

Java 9 improved the clock resolution so Instant.now() captures microsecond precision on most platforms (nanosecond on some). The old currentTimeMillis() only gives milliseconds.

HexFormat

Java 8

// Pad to 2 digits, uppercase
String hex = String.format(
    "%02X", byteValue);
// Parse hex string
int val = Integer.parseInt(
    "FF", 16);

Java 17+

var hex = HexFormat.of()
    .withUpperCase();
String s = hex.toHexDigits(
    byteValue);
byte[] bytes =
    hex.parseHex("48656C6C6F");

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JDK 17+ →

Date/Time Beginner

java.time API basics

Pre-Java 8

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

Java 8+

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+ →

Date/Time Beginner

Duration and Period

Pre-Java 8

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

Java 8+

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+ →