1. Short history of time
Tomasz Nurkiewicz
|
2013­07­09T16:35:50.090Z
nurkiewicz@gmail.com @tnurkiewicz

2. Tomasz Nurkiewicz
|
6+ years with Java
Scala, JavaScript, Clojure...
Back­end, data analysis and visualization
|
Used to be active on
Third time speaker on Javarsovia/Confitura
Working in Oslo ( )
nurkiewicz.blogspot.com
nurkiewicz@gmail.com @tnurkiewicz
scala.net.pl github.com/nurkiewicz
StackOverflow
we are hiring!

3. Bad day at Microsoft
blogs.msdn.com/b/windowsazure/archive/2012/03/09/summary­of­windows­azure­service­disruption­on­feb­29th­2012.aspx

4. Program result?
Java:
C#:
Calendar cal = new GregorianCalendar(2012, FEBRUARY, 29, 15, 0);
cal.add(YEAR, 1);
System.out.println(cal.getTime());
DateTime cal = new DateTime(2012, 2, 29, 15, 0, 0).AddYears(1);
Console.WriteLine(cal);

5. February 28th, 2013, 15:00
February 29th, 2013, 15:00
March 1st, 2013, 00:00
March 1st, 2013, 15:00
IllegalArgumentException

6. True story
“[...] in accordance with Terms and Conditions [...] interest is paid
for actual number of days funds were on account [...] however it is
assumed that year consists of 365 days.
Year 2012 has 366 days, thus
interest is not paid for 29th of February.
Yours faithfully, [some] Bank”
samcik.blox.pl/2012/03/Dzien­ktorego­nie­ma­Sprawdz­co­bank­wykreslil.html

7. Bad second for Linux
www.greenprophet.com/2012/07/leap­second­bug­consumes­megawatts­of­electricity/

8. Leap seconds
en.wikipedia.org/wiki/Leap_second

9. Inne błędy
Problem of year 2000 (Y2K)
Problem of year 2011 (Taiwan)
Problem of year 2038 (Integer.MAX_VALUE)
Problem of year 2042 (IBM S/370)
Problem of year 2107 (MS­DOS FAT)
Problem of September 9th, '99 (9/9/99)
en.wikipedia.org/wiki/Time_formatting_and_storage_bugs

10. Understand the domain
...of every problem

11. Date representation
www.edali.org/persistence­of­memory.jsp

12. Seconds since arbitrary moment in time
Calendar system

13. Time axis

14. Time "0"?
Date Used in
0. January 0 MATLAB
1. January 0 Symbian, Turbo DB
1. January 1 Microsoft .NET, Go
1. January 1601 NTFS, COBOL, Win32/Win64
1. January 1753 Microsoft SQL Server
31. December 1840 MUMPS
17. November 1858 VMS, United States Naval Observatory, DVB SI, astronomia
30. December 1899 Microsoft COM DATE, Object Pascal
0. January 1900 Microsoft Excel, Lotus 1­2­3
1. January 1900 NTP, IBM CICS, Mathematica, RISC OS, Common Lisp
1. January 1904 LabVIEW, Mac OS 9, Palm OS, MP4
1. January 1950 SEGA Dreamcast
Date Used in
1. January 1960 S­Plus, SAS
31. December 1967 Pick OS
1. January 1970 Linux, Mac OS X, C, Java, JavaScript,
Perl, PHP, Python, Tcl, ActionScript
1. January 1978 AmigaOS
1. January 1980 DOS, OS/2, FAT16 I FAT32, VOS
6. January 1980 Qualcomm BREW, GPS
1. January 1981 Acorn NetFS
1. January 1984 CiA® CANopen®
22. August 1999 Satelita Galileo
1. January 2000 PostgreSQL, AppleSingle, AppleDouble
1. January 2001 Apple Cocoa
en.wikipedia.org/wiki/Epoch_date

15. java.util.Date
:
vs.
:
en.wikipedia.org/wiki/Calendar_date
“A date in a calendar is a reference to a particular day
represented within a calendar system. [...] A particular day may
be represented by a different date in another calendar”
docs.oracle.com/javase/7/docs/api/java/util/Date.html
“The class Date represents a specific instant in time, with
millisecond precision.”

16. Time zones
java.util.Timezone

17. Time difference between Warsaw and Sydney?
www.travel.com.hk/region/timezone.htm

18. DST (Daylight saving time)
en.wikipedia.org/wiki/Daylight_saving_time

19. Daylight saving time
Winter → Summer Summer → Winter
en.wikipedia.org/wiki/Daylight_saving_time

20. ...so?
www.travel.com.hk/region/timezone.htm

21. Representation
WRONG!
final TimeZone tz = TimeZone.getTimeZone("Europe/Warsaw");
TimeZone.getTimeZone("GMT+01:00");
TimeZone.getTimeZone("Europe/warsaw");

22. Calendar date
java.util.Calendar

23. Leap years - WRONG!
def leapYear(year: Int): Boolean =
year % 4 == 0

24. Leap years - poor
def leapYear(year: Int): Boolean =
(year % 4 == 0 && year % 100 != 0) ||
(year % 400 == 0)

25. Leap years
def leapYear(year: Int): Boolean =
new GregorianCalendar(year, JANUARY, 1).
getActualMaximum(DAY_OF_YEAR) > 365

26. Puzzle
Calendar c = Calendar.getInstance();
System.out.println(c.get(Calendar.YEAR));

27. We have (Gregorian) year 2013
Meanwhile in Thailand...
...and in Japan...
$ java ...
2013
$ java -Duser.country=TH -Duser.language=th ...
2556
$ java -Duser.country=JP -Duser.language=ja -Duser.variant=JP ...
25

28. Better:
Even better:
Just in case...
Calendar c = new GregorianCalendar();
Calendar c = new GregorianCalendar(timeZone);
Calendar c = new GregorianCalendar(timeZone, locale);

29. Datevs. Calendar?
"...after some another event"
"...within 10 seconds"
"...within an hour"
"...within 24 hours"
"...within one day"
"...in 2013"
"...after 17:00"
"...on Friday"

30. Practice

31. Joda Time
final DateTime yearLater = new DateTime(2012, 2, 29, 15, 0).plusYears(1);
joda­time.sourceforge.net

32. Joda Time and JAX-WS
import org.joda.time.DateTime;
import javax.xml.bind.DatatypeConverter;
public class XsdJodaTimeConverter {
public static DateTime unmarshal(String dateTime) {
final long millis = DatatypeConverter.
parseDate(dateTime).
getTimeInMillis();
return new DateTime(millis);
}
public static String marshal(DateTime calendar) {
return DatatypeConverter.printDate(
calendar.toGregorianCalendar()
);
}
}

33. JAX-WS: .xjbfile
<bindings version="1.0" xmlns="http://java.sun.com/xml/ns/jaxb" xmlns:xs="http://www.w3.org/2001/XMLSchema">
<globalBindings>
<javaType xmlType="xs:dateTime"
name="org.joda.time.DateTime"
parseMethod="XsdJodaTimeConverter.unmarshal"
printMethod="XsdJodaTimeConverter.marshal"/>
</globalBindings>
</bindings>

34. Joda Time and JPA 2.1
import org.joda.time.Instant;
import javax.persistence.AttributeConverter;
import javax.persistence.Converter;
import java.util.Date;
@Converter(autoApply = true)
public class JodaTimeConverter implements AttributeConverter<Instant, Date> {
@Override
public Date convertToDatabaseColumn(Instant attr) {
return attr != null? attr.toDate(): null;
}
@Override
public Instant convertToEntityAttribute(Date dbData) {
return dbData != null? new Instant(dbData): null;
}
}

35. Testing - tools
Controlled time source ( )
"Exotic" default time zone
Don't sleep! (Thread.sleep()),
ScalaCheck
fake system clock
Awaitility

36. Testing - edge cases
Beginning/end of month/year
Weekends
29th of February
Time zones, DST

37. ScalaCheck and ScalaTest
Negative result
implicit override val generatorDrivenConfig =
PropertyCheckConfig(minSuccessful = 10000, workers = 4)
test("any date +1 year and -1 year should yield same date back") {
check {
random: Date => {
val plusMinusYear = new GregorianCalendar
plusMinusYear.setTime(random)
plusMinusYear.add(YEAR, 1)
plusMinusYear.add(YEAR, -1)
random == plusMinusYear.getTime
}
}
}
Falsified after 2665 passed tests:
arg0 = Mon Feb 29 03:21:22 CET 73843340

38. Events in the future
, , ...
Quartz
JMS
Activiti jBPM

39. Quartz scheduler
newTrigger()
.startAt(futureDate(1, YEAR))
.build();
quartz­scheduler.org/documentation/quartz­2.1.x/tutorials/tutorial­lesson­05

40. JMS with delay
MessageProducer producer = session.createProducer(destination);
TextMessage message = session.createTextMessage("...hello, delayed!");
message.setLongProperty(ScheduledMessage.AMQ_SCHEDULED_DELAY, oneYearMillis);
producer.send(message);
http://activemq.apache.org/delay­and­schedule­message­delivery.html

41. Bonus / Computus
(defn easter [year]
(let [
a (mod year 19)
b (Math/floor (/ year 100))
c (mod year 100)
d (Math/floor (/ b 4))
e (mod b 4)
f (Math/floor (/ (+ b 8) 25))
g (Math/floor (/ (inc (- b f)) 3))
h (mod (+ (- (+ (* 19 a) b) d g) 15) 30)
i (Math/floor (/ c 4))
k (mod c 4)
L (mod (- (+ 32 (* 2 e) (* 2 i)) h k) 7)
m (Math/floor (/ (+ a (* 11 h) (* 22 L)) 451))
n (- (+ h L 114) (* 7 m))
month (dec (Math/floor (/ n 31)))
day (inc (mod n 31))]
(java.util.GregorianCalendar. year month day)))
en.wikipedia.org/wiki/Computus

42. Bugs, more bugs...
1. "Due to the lack of [time] synchronization [...] a car bomb went off [...] one hour earlier than
expected" ( )
2. "F­22 Raptors [...] experienced multiple computer crashes coincident with their crossing of
[...] the International Date Line" ( )
3. "Damage to a German steel facility occurred during a DST transition" (
)
4.
5.
6. Unjustified fraud accusation ( ­ [37])
7. Catalog of few hundred bugs, up to year 2000 (!) (
)
catless.ncl.ac.uk/Risks/20.58.html#subj12
en.wikipedia.org/wiki/List_of_software_bugs
en.wikipedia.org/wiki/Daylight_Savings_Time
www.wired.com/wiredenterprise/2012/07/leap­second­bug­wreaks­havoc­with­java­
linux
www.theregister.co.uk/2012/07/02/leap_second_crashes_airlines
www.cs.tau.ac.il/~nachumd/horror.html
www.csl.sri.com/users/neumann/cal.html

43. Interesting and useful
1. ­ everything about time
2. ­ UNIX time
3. ­ foundation for this presentation
4. ­ definitions of TAI, UT, UTC...
5. ­ Samoa and Tokelau skip a day for dateline
change
www.timeanddate.com
www.epochconverter.com
www.odi.ch/prog/design/datetime.php
tycho.usno.navy.mil/systime.html
www.bbc.co.uk/news/world­asia­16351377

44. Thank you for your... time!
Twitter:
nurkiewicz@gmail.com
@tnurkiewicz
nurkiewicz.github.io/talks/confitura2013