A Quick peek @ New Date & Time API of Java 8

New Date & Time API of Java8
- Buddha Jyothiprasad

Agenda
 A Quick look at Old API
for Date and Time
 Discuss the issues with
it
 Introduce the new API
from Java 8
 See some examples of
various concepts in new
API
Buddha Java User Group - Hyderabad

A Quick Look at old API
 java.util.Date
 java.sql.Date
 Calendar
 GregorianCalendar
 TimeZone
 DateFormat
 SimpleDateFormat
Some bugs that doesn’t look like Bugs with old
API
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Issues with the old approach
Ø Date is actually DateTime
Ø Different class for SQL
Ø Date doesn’t have timezone
Ø getMonth() is zero-based, getYear() is 1900-based
(i.e., the year 2009 is represented as 109)
Ø Mutable hence not thread-safe by default
Ø java.util.Date represents an instant on the timeline
but invoking toString() prints time stamp along with
time zone, causing confusion among developers
Ø Calendar can’t format date directly
Ø Arithmetic operations are still tricky

Fixed Code that doesn’t look right

New API
 New package java.time
 New classes LocalDate,
LocalTime
 A composite class
LocalDateTime
 Supports numerous
ways of creating Date
and Time objects
 Supports Truncation,
Timezones, Periods,
Durations, Chronologies
ANSI SQL Java SE 8
DATE LocalDate
TIME LocalTime
TIMESTAMP LocalDateTime
TIME WITH TIMEZONE OffsetTime
TIMESTAMP WITH
TIMEZONE
OffsetDateTime
And many more….

Java 8 packages for Date & Time
• Consists of major base classes
• LocalDate, LocalTime, Instant, Duration
java.time
• Consists of generic API for non ISO Calendar
Systems java.time.chrono
• Contains temporal objects to find out specific
date/time related like firstDay of month java.time.temporal
• Classes for formatting and parsing date time
objects java.time.format
java.time.zone • Classes for supporting different timezones

Creating Objects
 All the core classes are
constructed by fluent
factory methods
 When constructing a
value by its constituent
fields, the factory is
called of
 when converting from
another type, the factory
is called from
 There are also parse
methods that take strings
as parameters
 Standard Java getter
conventions are used in
order to obtain values

Code for Creating Date & Time Objects

Date & Time manipulation
 We can alter the object
values in order to perform
calculations
 All objects are immutable
 Setters are no more
 New API also has a
concept of Adjuster
methods
 These methods are called
with and return new
objects
 There are also plus
adjusters
 We can write our own with
adjusters and plus
adjusters

Date Manipulation examples

Time Zones
 The local classes that we
looked at previously
abstract away the
complexity introduced by
time zones
 ZonedDateTime is a date
and time with a fully
qualified time zone
 This can resolve an offset
at any point in time
 Other classes are ZoneId,
ZoneOffset,
OffsetDateTime,
12OffsetTime Java User Group - Hyderabad

Time Zone examples

Instant, Periods & Duration
 Instant is the closest sibling of java.util.Date. Instant
class is used to work with machine readable time
format, it stores date time in unix timestamp.
 A Period represents a value such as “3 months and
1 day,”
 A Duration is a distance on the timeline measured in
terms of time, and it fulfills a similar purpose
to Period, but with different precision

Code snippets

Parsing & Formatting
 Every class in date time
formatter has methods for
parsing and formatting
 format() and parse()
directly on the date
objects
 DateTimeFormatter
 Loads of Predefined
formatters like ISO_DATE
 Custom formats can also
be provided via
DateTimeFormatter.ofPa
ttern() method

Parsing & Formatting snippets

Query
 A TemporalQuery can be used to retrieve
information from a temporal-based object
 The TemporalQueries class(note the plural)
provides several predefined queries
 The precision query, for example, returns the
smallest ChronoUnit that can be returned by a
particular temporal-based object
 We can also create custom queries by implementing
the interface TemporaryQuery

Working with Custom Queries

Legacy Support
 Legacy Date/Time
classes are used in
almost all the
applications
 Backward compatibility
is a must
 Following Utility
methods are provided
for that purpose
 toInstant()
 toZoneId()
 from()

Summary
 Immutability: All the classes in the new API are immutable hence
they are thread-safe.
 Separation of Concerns: The new API separates clearly between
human readable date time and machine time. It defines separate
classes for Date, Time, DateTime, Timestamp etc.
 Consistency: The methods are clearly defined and perform the
same action in all the classes. There are format() and parse()
methods defined in all these classes rather than having a separate
class for them.
 Utility operations: All the new Date Time API classes comes with
methods to perform common tasks, such as plus, minus, format,
parsing, getting separate part in date/time etc.
 Extendable: The new Date Time API works on ISO-8601 calendar
system but we can use it with other non ISO calendars as well.

Sources
 https://www.youtube.com/watch?v=OIg9lNpMJew
 http://www.oracle.com/technetwork/articles/java/jf14-
date-time-2125367.html
 http://docs.oracle.com/javase/8/docs/api/java/time/fo
rmat/DateTimeFormatter.html
 http://www.journaldev.com/2800/java-8-date-time-api-
example-tutorial-localdate-instant-localdatetime-parse-
and-format

A Quick peek @ New Date & Time API of Java 8

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