Presentation from Java 8 Date and Time hacking event on Kiev JUG meet up during EPAM IT Week

1. Speaker:
Oleg
Tsal-­‐Tsalko(@tsaltsol)
Java
8
Date
&
Time
API
(based
on
Stephen
Colebourne
Java
8
launch
talk)

2. About
me
Oleg
Tsal-­‐Tsalko
Lead
So:ware
Engineer
at
EPAM
Systems.
Speaker,
acEve
member
of
Kiev
JUG.
ParEcipate
in
different
educaEonal
iniEaEves
and
JCP/AdoptJSR
programs.

3. Overview
• JSR-­‐310:
New
Date
&
Time
API
• Replaces
old
ambiguous
java.uEl.Date,
Calendar,
TimeZone,
DateFormat
classes
• More
fluent/simple/clean
API
• Immutable
classes
• Using
Java8
features
including
lambdas
• Precise
separaEon
of
concepts

4. Range
of
types
• LocalDate
–
a
date
only
• LocalTime
–
a
Eme
only
• LocalDateTime
–
date
with
Eme
• ZonedDateTime
–
date
with
Eme
in
Eme
zone
• And
more…

5. LocalDate
Stores
year-­‐month-­‐day
Use
cases:
birthdays,
start/end
dates,
holidays
dates
LocalDate
current
=
LocalDate.now();
LocalDate
date
=
LocalDate.of(2014,
Month.AUGUST,
10);
If
(current.isA:er(date))…
boolean
leap
=
date.isLeapYear();
int
monthLength
=
date.lengthOfMonth();

6. Dates
manipulaEon
Because
LocalDate
is
immutable
we
have
plus/minus/with
methods
instead
add/set
methods:
date
=
date.plusMonth(1).minusDays(5);
date
=
date.withDayOfMonth(1);
date
=
date.with(Month.SEPTEMBER);

7. Using
adjusters
For
more
complex
dates
manipulaEons
we
use
many
predefined
TemporalAdjusters
or
create
custom
ones:
date
=
date.with(TemporalAdjusters.lastDayOfMonth());
date
=
date.with(next(TUESDAY))

8. LocalTime
Stores
hour-­‐minute-­‐second-­‐nanosecond
Use
cases:
shop
openning
hous,
clock
alarms,
etc.
LocalTime
current
=
LocalTime.now();
LocalTime
Eme
=
LocalTime.of(13,30);
If
(current.isBefore(Eme))
…
Eme
=
Eme.plusHours(4).plusMinutes(10).minusSeconds(30);
Eme
=
Eme.truncatedTo(SECONDS);

9. LocalDateTime
Basically
combinaEon
of
LocalDate
and
LocalTime.
All
methods
are
similar
to
LocalDate
and
LocalTime…

10. TimeZones
We
have
numerous
of
TimeZones
governed
by
poliIcal
rules
which
someEmes
complex
and
might
change
frequently.
If
you
can
avoid
using
TimeZones
–
do
it!

11. TimeZone
classes
in
Java
8
• ZoneId
–
replacement
for
TimeZone
class
(e.g.
“Europe/London”,
“Europe/Kiev”)
• ZoneOffset
–
represenEng
offset
from
UTC
Eme
• ZoneRules
–
behind
the
scenes
class
which
defines
Eme
zone
rules
• ZonedDateTime
–
main
date/Eme
class
which
is
aware
of
Eme
zones

12. ZonedDateTime
Internaly
stores
LocalDateTime,
ZoneId
and
ZoneOffset
and
is
closest
equivalent
to
java.u2l.GregorianCalendar.
zone
=
ZoneId.of(“Europe/London”);
zonedDateTime
=
ZonedDateTime.of(2014,
AUGUST,
10,
13,
30,
0,
0,
zone);
zonedDateTime.plusDays(1).minusMinutes(30);
Takes
care
of
‘daylight
savings’
and
no
excepEons
thrown
in
ambigue
cases
instead
act
on
best
effort
basis

13. Calendar
systems
• All
main
classes
use
ISO
calendar
system
• Other
calendar
systems
(Hijrah,
Japanese,
Minguo,
ThaiBuddist,
etc.)
also
supported
however
not
at
the
same
degree
and
might
be
complicated
to
use.
• Good
thong
is
that
diff
calendar
systems
separated
from
each
other
• Main
interfaces
to
be
implemented
for
new
calendar
systems
are:
Cronology
and
ChronoLocalDate

14. Power
of
abstracEon
New
API
is
very
flexible
because
it
based
on
number
of
abstracEons
at
it’s
bopom:
• Temporal
–
parent
class
for
all
date/Eme
objects
which
defines
mutaEon
operaEon
for
them
such
as
plus/
minus/with
• TemporalAdjuster
–
funcEonal
interface
which
responsible
for
mutaEng
Temporal
objects
• TemporalField
–
represents
parts/fields
of
date/Eme
objects
such
as
(DAY_OF_WEEK,
MONTH,
etc.)
• TemporalUnit
–
represents
type
of
date/Eme
values
such
as
(MINUTES,
DAYS,
YEARS,
etc.)
• TemporalAmount
–
class
which
represents
amount
of
Eme

15. DuraEon
Time-­‐based
amount
of
Eme
in
hours,
minutes,
seconds
or
nanoseconds.
Use
cases:
Emeouts
duraEon
=
DuraEon.ofHours(6);
duraEon
=
duraEon.mulEpliedBy(3);
duraEon
=
duraEon.plusMinutes(30);
date
=
LocalDateTime.now();
Date.plus(duraEon);

16. Period
Date-­‐based
amount
of
Eme
in
years,
months,
days.
Use
cases:
length
of
holiday,
length
of
trip
period
=
Period.ofMonth(9);
period
=
period.plusDays(6);

17. Links
• hpps://today.java.net/pub/a/today/2008/09/18/
jsr-­‐310-­‐new-­‐java-­‐date-­‐Eme-­‐api.html
• hpp://blog.joda.org/2009/11/why-­‐jsr-­‐310-­‐isn-­‐
joda-­‐Eme_4941.html
• hpps://blogs.oracle.com/thejavatutorials/entry/
javaone_2013_jdk_8_date
• hpp://vimeo.com/87157763
• hpp://parleys.com/play/
52508380e4b0c4f11ec57665/about
• hpp://www.oracle.com/events/us/en/java8/
index.html

18. Thank
you!
Oleg
Tsal-­‐Tsalko
Email:
oleg.tsalko@gmail.com
Twiper:
@tsaltsol