A lightning talk that I presented to the London Java Community on JSR-310

1. LJC/JCP Committee
Java Dating
By James Gough
Thursday, 14 July 2011

2. LJC/JCP
• Who am I?
• What is the LJC/JCP?
• Why get involved?
Thursday, 14 July 2011

3. Who am I?
• James Gough
• jpgough@gmail.com
• Twitter: goughjam
• Java developer for 8 years, 4 years industry experience
• Work at a large investment bank developing Flex and Java
• Run my own company in spare time developing iOS
applications
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Thursday, 14 July 2011

4. LJC/JCP
• LJC recently elected onto the JCP committee
• JCP (Java Community Process)
• The JCP is the mechanism for developing
standard technical specifications for the
Java technology
• Interested? Ben Evans @kittylst on twitter, or
find me at the bar on Tuesday
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Thursday, 14 July 2011

5. Why get involved?
• Chance to have a say
• Discover more about Java and the
inner workings
• Get involved on projects and
contribute to Java directly
• Offered to do a lightning talk
• Coming soon: Java memory pub
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Thursday, 14 July 2011

6. Dates?
• The thing that's bothering me at the
moment is dating, there’s several things
to be aware of:
• Choosing a good restaurant
• What to wear
• ....
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Thursday, 14 July 2011

7. Java Dates
• Java Date and Calendar
• Joda Time
• JSR-310
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Thursday, 14 July 2011

8. Java Date
• Java Date has been in the language since January 23, 1996
• Many good discussions about what’s wrong with dates
• Mutability
• Date is a DateTime, but there are other classes for SQL
• No Timezones
• Not easy to use
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Thursday, 14 July 2011

9. Calendar
• Still mutable
• Can’t format a date directly
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Thursday, 14 July 2011

10. Example From It’s High Time
@JavaOne 2008
• How many bugs in this code?
Date date = new Date(2007, 12, 13, 16,
40);
TimeZone zone = TimeZone.getInstance
("Asia/HongKong");
Calendar cal = new GregorianCalendar
(date, zone);
DateFormat fm = new SimpleDateFormat
("HH:mm Z");
String str = fm.format(cal);
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Thursday, 14 July 2011

11. Example From It’s High Time
@JavaOne 2008
• 6 bugs in the code!
Date date = new Date(2007, 12, 13, 16,
40);
TimeZone zone = TimeZone.getInstance
("Asia/Hong_Kong");
Calendar cal = new GregorianCalendar
(date, zone);
DateFormat fm = new SimpleDateFormat
("HH:mm Z");
String str = fm.format(cal);
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Thursday, 14 July 2011

12. Joda Time
• Instant
• Moment in time, represented by DateTime. DateTime
is immutable
• Interval
• An interval of time from one instant to another. Both
end points have same Chronology and TimeZone
• Duration
• Duration of time measured in milliseconds. No
timezone of chronology applies
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Thursday, 14 July 2011

13. Joda Time
• Period
• A period of time defined in terms of fields (e.g. +1 month)
• Chronology
• A calculation engine supporting complex calendar rules
• In most this can be ignored, important to the internal design, but
not to the standard user using ISOChronology
• Timezones
• DateTimeZone zone = DateTimeZone.forID
("Europe/London");
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Thursday, 14 July 2011

14. JSR-310
• Human/Machine Timelines
• Requirement to have a separation of concerns
between human and machine timelines
• DateTime is better thought of as a LocalDateTime and
a timezone
• Pluggable Chronology
• Restrict DateTime classes to a single calendar system
• Nulls
• Null means 0 in most cases, ouch!
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Thursday, 14 July 2011

15. Getting Involved
• ThreeTen is now on GitHub
• Open project that can be contributed to
• A few pull requests have been made since moving to
GitHub
• Accept the legal agreement
• Mailing List: threeten-
develop@lists.sourceforge.net
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16. Contact
• James Gough
• jpgough@gmail.com
• Twitter: goughjam
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Thursday, 14 July 2011