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Java8 Features - Date and Time API enhancements

Date and Time API - JSR 310 - Need for the enhancement

Anybody who has worked with Java date, calendar and time prior to java8 has had to google at least a few times before their code worked fine. that was how tedious or non-intuitive the entire code surrouding the date and time model was. 

Secondly, the objects related to date time were all mutable, causing issues in multithreaded functionalities. (classic example use of SimpleDateFormat.parse()).

Third, missing common operations like finding time in TZ x knowing current time in TZ y, month, day, year operations on date etc.

Updates in java8

Completely new model of date and time based on the calendar system defined in ISO-8601. java.time.* package 
Two types of times:
  • human time (LocalDate, LocalTime, LocalDateTime, ZonedDateTime,Period)
  • continuous time / unix timestamp (Instant, duration)
One can implement their own calendar system by extending the ChronoLocalDate.

Sample code

Ease of doing date manipulations:
 //code to print next Friday  
 LocalDate today= LocalDate.now();
 System.out.println(today.plusWeeks(1).with(TemporalAdjusters.next(DayOfWeek.FRIDAY)));

Ease of doing formatting
 LocalDateTime now = LocalDateTime.now();
 System.out.println(now.format(DateTimeFormatter.ofPattern("dd/MM/yyyy HH:mm:ss")));

 Ease of date parsing
 LocalDate d3 = LocalDate.parse("18/07/2017",DateTimeFormatter.ofPattern("dd/MM/yyyy"));
 System.out.println(d3);

 Ease of period /duration between 2 dates:
 LocalDate travelDate=LocalDate.of(2015, Month.NOVEMBER, 21);
 LocalDate returnDate = LocalDate.now();
 Period travelPeriod = Period.between(travelDate, returnDate);
 System.out.println("You were travelling for a period of "+travelPeriod.getYears()+" years and "+travelPeriod.getMonths()+ " months and  "+travelPeriod.getDays()+" days ( total of "+ChronoUnit.DAYS.between(travelDate, returnDate)+" days)");

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