Working with Dates and Time in Kotlin: A Complete Guide

Introduction to working with dates and time in Kotlin

Working with dates and time is one of the key tasks in developing any application. Whether it's event logging, calculating deadlines, displaying a calendar, or working with timestamps, you can't do without a reliable toolkit. In the Kotlin ecosystem, the powerful java.time library is used for these purposes, which replaced the outdated java.util.Date and java.util.Calendar. Thanks to full compatibility with Java, Kotlin allows you to use all the features of java.time directly, and also adds convenient extensions and syntactic sugar.

In this article, we will take a detailed look at how to create, format, parse, and convert dates and time in Kotlin. You will learn about key classes such as LocalDate, LocalTime, LocalDateTime, ZonedDateTime, and Instant, and also learn how to work with periods and durations. All code examples are written in pure Kotlin and are ready to use.

Main classes for working with dates and time

The java.time library offers several key classes, each of which solves its own task. Let's look at them in more detail.

LocalDate — working with date without time

The LocalDate class represents a date (year, month, day) without considering time and time zone. It is ideal for birthdays, calendar events, and tasks where time does not matter.

import java.time.LocalDate

fun main() {    // Current date    val today = LocalDate.now()    println("Today: $today")

    // Specific date    val specificDate = LocalDate.of(2024, 12, 25)    println("Christmas: $specificDate")

    // Parsing from string    val parsedDate = LocalDate.parse("2024-12-25")    println("Parsed: $parsedDate")}

LocalTime — working with time without date

LocalTime stores only time (hours, minutes, seconds, nanoseconds). It is used for schedules, timers, and timestamps without binding to a date.

import java.time.LocalTime

fun main() {    // Current time    val now = LocalTime.now()    println("Now: $now")

    // Specific time    val lunchTime = LocalTime.of(13, 30)    println("Lunch at: $lunchTime")

    // Parsing    val parsedTime = LocalTime.parse("15:45:30")    println("Parsed: $parsedTime")}

LocalDateTime — combining date and time

LocalDateTime combines LocalDate and LocalTime. This is the most commonly used class for storing a point in time without considering the time zone.

import java.time.LocalDateTimeimport java.time.LocalDateimport java.time.LocalTime

fun main() {    // Current moment    val now = LocalDateTime.now()    println("Now: $now")

    // From individual components    val date = LocalDate.of(2024, 12, 25)    val time = LocalTime.of(10, 0)    val christmasMorning = LocalDateTime.of(date, time)    println("Christmas morning: $christmasMorning")

    // Combined method    val newYear = LocalDateTime.of(2025, 1, 1, 0, 0)    println("New Year: $newYear")}

Formatting and parsing dates

To convert dates to strings and back, the DateTimeFormatter class is used. It supports many predefined formats and also allows you to create custom patterns.

Formatting a date into a string

import java.time.LocalDateTimeimport java.time.format.DateTimeFormatter

fun main() {    val now = LocalDateTime.now()

    // Standard ISO format    val isoFormat = now.format(DateTimeFormatter.ISO_LOCAL_DATE_TIME)    println("ISO: $isoFormat")

    // Custom format    val customFormatter = DateTimeFormatter.ofPattern("dd.MM.yyyy HH:mm:ss")    va