A big part of developer community has been complaining about Date and Calendar classes. Reasons were many such as hard to understand, hard to use and not flexible. Date class has even become obsolete and java docs suggest to use Calendar class instead of Date class. And on top of all, Date comparison is buggy and I have also faced such issue in past.
Moving forward, JAVA 8 (Lambda) is expected to release the new Date and Time APIs/classes (JSR-310), also called as ThreeTen, which will simply change the way you have been doing till date. This A key part of this is providing a new API that is dramatically easier to use and less error prone.
It will provide some highly demanded features such as:
- All the key public classes are immutable and thread-safe
- Defined terminology and behavior that other areas in computing can adopt
TemporalAdjuster.java. Previously it was a class, now it is a @FunctionalInterface. So, I have corrected the related example and used the class “TemporalAdjusters.java“.Table of Contents New classes to represent local date and timezone New classes to represent timestamp and duration Added utility classes over existing enums Date adjusters introduced Building dates will be easier New class to simulate system/machine clock Timezone handling related changes Date formatting changes References
New classes to represent local date and timezone
The new classes intended to replace Date class are LocalDate, LocalTime and LocalDateTime.
LocalDate
The LocalDate class represents a date. There is no representation of a time or time-zone.
LocalDate localDate = LocalDate.now(); System.out.println(localDate.toString()); //2013-05-15 System.out.println(localDate.getDayOfWeek().toString()); //WEDNESDAY System.out.println(localDate.getDayOfMonth()); //15 System.out.println(localDate.getDayOfYear()); //135 System.out.println(localDate.isLeapYear()); //false System.out.println(localDate.plusDays(12).toString()); //2013-05-27
LocalTime
The LocalTime class represents a time. There is no representation of a date or time-zone.
//LocalTime localTime = LocalTime.now(); //toString() in format 09:57:59.744 LocalTime localTime = LocalTime.of(12, 20); System.out.println(localTime.toString()); //12:20 System.out.println(localTime.getHour()); //12 System.out.println(localTime.getMinute()); //20 System.out.println(localTime.getSecond()); //0 System.out.println(localTime.MIDNIGHT); //00:00 System.out.println(localTime.NOON); //12:00
LocalDateTime
The LocalDateTime class represents a date-time. There is no representation of a time-zone.
LocalDateTime localDateTime = LocalDateTime.now(); System.out.println(localDateTime.toString()); //2013-05-15T10:01:14.911 System.out.println(localDateTime.getDayOfMonth()); //15 System.out.println(localDateTime.getHour()); //10 System.out.println(localDateTime.getNano()); //911000000
If you want to use the date functionality with zone information, then Lambda provide you extra 3 classes similar to above one i.e. OffsetDate, OffsetTime and OffsetDateTime. Timezone offset can be represented in “+05:30” or “Europe/Paris” formats. This is done via using another class i.e. ZoneId.
OffsetDateTime offsetDateTime = OffsetDateTime.now(); System.out.println(offsetDateTime.toString()); //2013-05-15T10:10:37.257+05:30 offsetDateTime = OffsetDateTime.now(ZoneId.of("+05:30")); System.out.println(offsetDateTime.toString()); //2013-05-15T10:10:37.258+05:30 offsetDateTime = OffsetDateTime.now(ZoneId.of("-06:30")); System.out.println(offsetDateTime.toString()); //2013-05-14T22:10:37.258-06:30 ZonedDateTime zonedDateTime = ZonedDateTime.now(ZoneId.of("Europe/Paris")); System.out.println(zonedDateTime.toString()); //2013-05-15T06:45:45.290+02:00[Europe/Paris]
New classes to represent timestamp and duration
Instant
For representing the specific timestamp ant any moment, the class needs to be used is Instant. The Instant class represents an instant in time to an accuracy of nanoseconds. Operations on an Instant include comparison to another Instant and adding or subtracting a duration.
Instant instant = Instant.now(); System.out.println(instant.toString()); //2013-05-15T05:20:08.145Z System.out.println(instant.plus(Duration.ofMillis(5000)).toString()); //2013-05-15T05:20:13.145Z System.out.println(instant.minus(Duration.ofMillis(5000)).toString()); //2013-05-15T05:20:03.145Z System.out.println(instant.minusSeconds(10).toString()); //2013-05-15T05:19:58.145Z
Duration
Duration class is a whole new concept brought first time in java language. It represents the time difference between two time stamps.
Duration duration = Duration.ofMillis(5000); System.out.println(duration.toString()); //PT5S duration = Duration.ofSeconds(60); System.out.println(duration.toString()); //PT1M duration = Duration.ofMinutes(10); System.out.println(duration.toString()); //PT10M duration = Duration.ofHours(2); System.out.println(duration.toString()); //PT2H duration = Duration.between(Instant.now(), Instant.now().plus(Duration.ofMinutes(10))); System.out.println(duration.toString()); //PT10M
Duration deals with small unit of time such as milliseconds, seconds, minutes and hour. They are more suitable for interacting with application code.
Period
To interact with human, you need to get bigger durations which are presented with Period class.
Period period = Period.ofDays(6); System.out.println(period.toString()); //P6D period = Period.ofMonths(6); System.out.println(period.toString()); //P6M period = Period.between(LocalDate.now(), LocalDate.now().plusDays(60)); System.out.println(period.toString()); //P1M29D
Added utility classes over existing enums
The current Java SE platform uses int constants for months, day-of-week and am-pm etc. Now a lot of extra utility classes have been added which work on top of these enums. I am taking an example such a class DayOfWeek. This class is a wrapper of day enums and can be used consistently with other classes also.
DayOfWeek
//day-of-week to represent, from 1 (Monday) to 7 (Sunday) System.out.println(DayOfWeek.of(2)); //TUESDAY DayOfWeek day = DayOfWeek.FRIDAY; System.out.println(day.getValue()); //5 LocalDate localDate = LocalDate.now(); System.out.println(localDate.with(DayOfWeek.MONDAY)); //2013-05-13 i.e. when was monday in current week ?
Other such classes are Month, MonthDay, Year, YearMonth and many more.
Date adjusters
Date adjusters are another beautiful and useful addition in date handling tools. It easily solves the problems like : How do you find last day of the month? Or the next working day? Or a week on Tuesday?
Lets see in code.
LocalDate date = LocalDate.of(2013, Month.MAY, 15); //Today LocalDate endOfMonth = date.with(TemporalAdjusters.lastDayOfMonth()); System.out.println(endOfMonth.toString()); //2013-05-31 LocalDate nextTue = date.with(TemporalAdjusters.next(DayOfWeek.TUESDAY)); System.out.println(nextTue.toString()); //2013-05-21
Creating date objects
Creating date objects now can be done using builder pattern also. The builder pattern allows the object you want to be built up using individual parts. This is achieved using the methods prefixed by “at”.
//Builder pattern used to make date object OffsetDateTime date1 = Year.of(2013) .atMonth(Month.MAY).atDay(15) .atTime(0, 0) .atOffset(ZoneOffset.of("+03:00")); System.out.println(date1); //2013-05-15T00:00+03:00 //factory method used to make date object OffsetDateTime date2 = OffsetDateTime. of(2013, 5, 15, 0, 0, 0, 0, ZoneOffset.of("+03:00")); System.out.println(date2); //2013-05-15T00:00+03:00
New class to simulate system/machine clock
A new class Clock is proposed in new release. This simulates the system clock functionality. I loved this feature most of all others. The reason is while doing unit testing. you are often required to test a API in future date. For this we had been forwarding the system clock for next date, and then again restart the server and test the application.
Now, no need to do this. Use Clock class to simulate this scenario.
Clock clock = Clock.systemDefaultZone(); System.out.println(clock); //SystemClock[Asia/Calcutta] System.out.println(clock.instant().toString()); //2013-05-15T06:36:33.837Z System.out.println(clock.getZone()); //Asia/Calcutta Clock anotherClock = Clock.system(ZoneId.of("Europe/Tiraspol")); System.out.println(anotherClock); //SystemClock[Europe/Tiraspol] System.out.println(anotherClock.instant().toString()); //2013-05-15T06:36:33.857Z System.out.println(anotherClock.getZone()); //Europe/Tiraspol Clock forwardedClock = Clock.tick(anotherClock, Duration.ofSeconds(600)); System.out.println(forwardedClock.instant().toString()); //2013-05-15T06:30Z
Timezone Changes
Timezone related handling is done by 3 major classes. These are ZoneOffset, TimeZone, ZoneRules.
- The
ZoneOffsetclass represents a fixed offset from UTC in seconds. This is normally represented as a string of the format “±hh:mm”. - The
TimeZoneclass represents the identifier for a region where specified time zone rules are defined. - The
ZoneRulesare the actual set of rules that define when the zone-offset changes.
//Zone rules System.out.println(ZoneRules.of(ZoneOffset.of("+02:00")).isDaylightSavings(Instant.now())); System.out.println(ZoneRules.of(ZoneOffset.of("+02:00")).isFixedOffset());
Date Formatting
Date formatting is supported via two classes mainly i.e. DateTimeFormatterBuilder and DateTimeFormatter. DateTimeFormatterBuilder works on builder pattern to build custom patterns where as DateTimeFormatter provides necessary input in doing so.
DateTimeFormatterBuilder formatterBuilder = new DateTimeFormatterBuilder(); formatterBuilder.append(DateTimeFormatter.ISO_LOCAL_DATE_TIME) .appendLiteral("-") .appendZoneOrOffsetId(); DateTimeFormatter formatter = formatterBuilder.toFormatter(); System.out.println(formatter.format(ZonedDateTime.now()));
These are major changes which I was able to identify and worked on.
References
- https://jdk8.java.net/lambda/
- http://sourceforge.net/apps/mediawiki/threeten/index.php?title=User_Guide
Happy Learning !!
Pawan
thanks for updating