HexFormat

Convert between hex strings and byte arrays with HexFormat.

Code Comparison

✕ 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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Why the modern way wins

📐

Bidirectional

Convert bytes→hex and hex→bytes with one API.

🔧

Configurable

Delimiters, prefix, suffix, upper/lower case.

📦

Array support

Encode/decode entire byte arrays at once.

Old Approach

Manual Hex Conversion

Modern Approach

HexFormat

Since JDK

Difficulty

Intermediate

JDK Support

HexFormat

Available

Widely available since JDK 17 LTS (Sept 2021)

How it works

HexFormat provides bidirectional hex encoding/decoding for bytes, ints, and arrays. Configure delimiters, prefix, suffix, and case. No more manual formatting or parsing.

Date formatting

Pre-Java 8

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

Java 8+

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

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JDK 8+ →

Date/Time Intermediate

Instant with nanosecond precision

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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JDK 9+ →

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+ →