Java8 – Date and Time examples

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Java8 – Date and Time examples

This post originally appeared in my blog, www.javabullets.com as part of a series covering Java8 features.

We had two date implementations before Java8 – java.util.Date and java.util.Calendar. There were numerous issues with these implementations which Java8 seeks to resolve with its new java.time API.

Issues

API Design – java.util.Date and java.util.Calendar both had issues including -
- months starting from 0
- in the case of Date year starting from 1900
- Date also represented a point in time, seconds from the epoch, while its toString method included a TimeZone
- No single class representing Time or Date
DateFormat not thread safe

Joda-Time evolved as a defacto standard for Java dates, and its lead developer Stephen Colebourne defined the Java8 JSR-310 API.

Pre-Java8 Date and Calendar Examples

The following snippet demonstrates -

toString method contains a Timezone
Date - Month Starts at zero, and year at 1900
Calendar - Month still starts at zeron, but the year is now fixed

Note this will generate a deprecated API warning

// {
        Date today = new Date();
        System.out.println("Note the time includes the default timezone - " + today.toString());
        Date twentySevenFeb2017Date = new Date(117, 1, 27);
        System.out.println("Now deprecated new Date(day, month, year) - but note month starts at zero, and year 1900 - " + twentySevenFeb2017Date);
        Calendar twentySevenFeb2017Calendar = new GregorianCalendar(2017,1,27);
        System.out.println("Calendar - month starts at zero, and but year fixed - " + twentySevenFeb2017Calendar.getTime());
        DateFormat ddMMyyySDF = new SimpleDateFormat("dd/MM/yyyy");
        System.out.println("DateFormat not ThreadSafe - " + ddMMyyySDF.format(twentySevenFeb2017Date));
//{

New Features

New package – java.time.*
Core Classes – LocalDate, LocalTime, LocalDateTime, ZonedDateTime, Period, Duration, Instant
Immutable
Factory methods

LocalDate And LocalTime Examples

The following snippet demonstrates -

LocalDate - Date without Timezone
LocalTime - Time without Timezone

// {
    LocalDate currentLocalDate = LocalDate.now();
    System.out.println("currentLocalDate - yyyy-MM-dd - " + currentLocalDate);
    // Month now not based on 0, and year not based on 1900
    LocalDate twentySevenFeb2017LocalDate = LocalDate.of(2017, 2, 27);
    System.out.println("twentySevenFeb2017LocalDate - yyyy-MM-dd - " + twentySevenFeb2017LocalDate);
    twentySevenFeb2017LocalDate = twentySevenFeb2017LocalDate.withYear(2017).withMonth(12).withDayOfMonth(25);
    System.out.println("twentySevenFeb2017LocalDate - with -  " + twentySevenFeb2017LocalDate);
    LocalDate parseTwentySevenFeb2017LocalDate = LocalDate.parse("2017-02-27", DateTimeFormatter.ofPattern("yyyy-MM-dd"));
    System.out.println("parseTwentySevenFeb2017LocalDate - pattern - yyyy-MM-dd - " + parseTwentySevenFeb2017LocalDate);
    
    // increment using plus, decrement using minus
    twentySevenFeb2017LocalDate = twentySevenFeb2017LocalDate.plusDays(1);
    System.out.println("twentySevenFeb2017LocalDate - immutable - " + twentySevenFeb2017LocalDate);
    
    // Time with no date
    LocalTime currentLocalTime = LocalTime.now();
    System.out.println("currentLocalTime - yyyy-MM-dd - " + currentLocalTime);
    
    LocalTime parseLocalTime = LocalTime.parse("13:44");
    System.out.println("parseLocalTime - " + parseLocalTime);
    parseLocalTime = LocalTime.parse("13:44:25");
    System.out.println("parseLocalTime - immutable - " + parseLocalTime);
//{

LocalDateTime Examples

Combines LocalDate and LocalTime
Called through factory methods of, now, parse
Immutable
No TimeZone

// {
        LocalDateTime currentLocalDateTime = LocalDateTime.now();
        System.out.println("currentLocalDateTime " + currentLocalDateTime);     
        currentLocalDateTime = LocalDateTime.parse("2019-06-21T23:53:00.123");
        System.out.println("currentLocalDateTime - parse -  " + currentLocalDateTime);
        currentLocalDateTime = currentLocalDateTime.minusYears(10);
        System.out.println("currentLocalDateTime - minus 10 years -  " + currentLocalDateTime);
//{

ZonedDateTime

Associate DateTime with TimeZone

// {
        ZonedDateTime zonedDateTime = ZonedDateTime.of(LocalDateTime.now(), ZoneId.systemDefault());
        System.out.println("zonedDateTime - " + zonedDateTime);
        ZoneId australiaSydneyZoneId = ZoneId.of("Australia/Sydney");
        ZonedDateTime australiaSydneyZonedDateTime = ZonedDateTime.of(LocalDateTime.now(), australiaSydneyZoneId);
        System.out.println("australiaSydneyZonedDateTime - " + australiaSydneyZonedDateTime);
//{

CustomAdjuster

The adjuster will adjust a date according to the defined rule

Period Or Duration

Period - Duration in day, weeks, month, years
Duration - days, hours, minutes, seconds

// {
    // Period - Duration in day, weeks, month, years 
    Period examplePeriod = Period.of(72,6,10);
    System.out.println("examplePeriod " + examplePeriod);
    LocalDate localDatePlusExamplePeriod = LocalDate.now().plus(examplePeriod);
    System.out.println("localDatePlusExamplePeriod " + localDatePlusExamplePeriod);
    
    // Duration - days, hours, minutes, seconds
    Duration exampleDuration = Duration.ofHours(5);
    System.out.println("exampleDuration " + exampleDuration);
    
    LocalTime exampleDurationLocalTime = LocalTime.now().plus(exampleDuration);
    System.out.println("exampleDurationLocalTime " + exampleDurationLocalTime); 
//{

If you have liked this post, check out my personal blog which contains similar tutorials at www.javabullets.com

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Java8 – Date and Time examples

Issues

Pre-Java8 Date and Calendar Examples

New Features

LocalDate And LocalTime Examples

LocalDateTime Examples

ZonedDateTime

CustomAdjuster

Period Or Duration

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