DateTimeFormatter in Java

The DateTimeFormatter class in Java, in java.time.format, is used to format a date or time as text, such as turning 2026-11-12 into "12 Nov 2026", and to parse text back into a date or time. It replaces the old SimpleDateFormat, and unlike that class it is immutable and thread-safe, so one formatter can be shared everywhere. In this lesson, you will learn the built-in formatters, how to write your own patterns, and how to handle parsing errors.

Creating a Formatter

Pattern Letters

Example: Formatting

Let's see an example that formats one date and time in several ways.

import java.time.LocalDateTime;
import java.time.format.DateTimeFormatter;
import java.util.Locale;
 
public class Formatting {
    public static void main(String[] args) {
        LocalDateTime t = LocalDateTime.of(2026, 11, 12, 14, 47, 31);
 
        System.out.println(t.format(DateTimeFormatter.ISO_LOCAL_DATE_TIME));
        System.out.println(t.format(DateTimeFormatter.ofPattern("dd-MM-yyyy")));
        System.out.println(t.format(
            DateTimeFormatter.ofPattern("EEEE, d MMMM yyyy", Locale.ENGLISH)));
        System.out.println(t.format(
            DateTimeFormatter.ofPattern("hh:mm a", Locale.ENGLISH)));
        System.out.println(t.format(DateTimeFormatter.ofPattern(
            "'Exam on' dd MMM 'at' HH:mm", Locale.ENGLISH)));
        System.out.println(t.format(
            DateTimeFormatter.ofPattern("d MMMM yyyy", Locale.FRENCH)));
    }
}

2026-11-12T14:47:31
12-11-2026
Thursday, 12 November 2026
02:47 PM
Exam on 12 Nov at 14:47
12 novembre 2026

Explanation: The ISO formatter gives the standard machine format. Each pattern lays out the parts you choose. Words in single quotes are copied as they are. The locale decides the language of month and day names, so the same pattern gives "November" in English and "novembre" in French.

Example: Parsing

import java.time.LocalDate;
import java.time.LocalTime;
import java.time.format.DateTimeFormatter;
import java.time.format.DateTimeParseException;
import java.time.format.ResolverStyle;
 
public class Parsing {
    public static void main(String[] args) {
        DateTimeFormatter indian = DateTimeFormatter.ofPattern("dd/MM/yyyy");
 
        LocalDate birthday = LocalDate.parse("15/03/2012", indian);
        System.out.println("Parsed: " + birthday + ", a "
            + birthday.getDayOfWeek());
 
        LocalTime alarm = LocalTime.parse("06:30");
        System.out.println("Alarm: " + alarm);
 
        System.out.println("Smart: " + LocalDate.parse("31/02/2026", indian));
 
        DateTimeFormatter strict = DateTimeFormatter.ofPattern("dd/MM/uuuu")
            .withResolverStyle(ResolverStyle.STRICT);
        try {
            LocalDate.parse("31/02/2026", strict);
        } catch (DateTimeParseException e) {
            System.out.println("Strict: " + e.getMessage());
        }
    }
}

Parsed: 2012-03-15, a THURSDAY
Alarm: 06:30
Smart: 2026-02-28
Strict: Text '31/02/2026' could not be parsed: Invalid date 'FEBRUARY 31'

Explanation: LocalDate.parse(text, formatter) reads text using the pattern. Without a formatter, parse expects ISO text such as "06:30". Note the surprise: by default, a formatter uses the smart resolver, which quietly turns 31 February into 28 February. A formatter with ResolverStyle.STRICT rejects it with DateTimeParseException. Strict mode needs uuuu (the proleptic year) instead of yyyy. Text that can never be valid, such as day 32, throws even in smart mode.

Common Mistakes

Writing "dd-mm-yyyy". mm is minutes; use MM for months.

Writing "YYYY". Y is the week-based year, which differs from the calendar year around New Year; use yyyy.

Validating user input with the default (smart) resolver. It turns 31 February into 28 February; use ResolverStyle.STRICT with uuuu.

Formatting month names without a locale. The result depends on the computer's language; pass Locale.ENGLISH or the user's locale.

Interview Corner

Practice

1. Easy: Format today's date as "Thursday 12/11/2026" and as "12th of November" (hint: build the "th" yourself).
2. Harder: Read dates typed in the format dd-MM-yyyy, ask again when the input is invalid, and print how many days remain until each date.

Key Takeaways