Java 8 features

Java 8 features presentation from JavaDay Lviv 2015

1. 10+ new features
you ought to know
using Java 8
Oleg Tsal-Tsalko
JavaDay Lviv 2015

2. LEAD SOFTWARE ENGINEER AT EPAM SYSTEMS.
PATIONATE DEVELOPER, SPEAKER, ACTIVE MEMBER OF
KIEV JUG.
PARTICIPATE IN DIFFERENT EDUCATIONAL INITIATIVES,
ENGINEERING EVENTS AND JCP/ADOPTJSR PROGRAMS.

OLEG TSAL-TSALKO
ABOUT ME

3. 3 CONFIDENTIAL
• Stream API
• Lambdas and method references
• Default methods
• Optional values
• Date & Time API
• Stamped Locks and Concurrent Adders
• Type annotations and repeated annotations
• New files operations
• Overflow operations and Base64 encoding
• Nashorn JavaScript engine
Agenda

4. 4 CONFIDENTIAL
• An abstraction that supports bulk operations
over sequence of elements
• Not a data structure
• Simple and logical chaining of operations
• Lazy evaluation
• Internal parallelism if required
• Concept of functional programming in Java

#1 Stream API

5. 5 CONFIDENTIAL
• Collection.stream()
• IntStream.range()
• Stream.of()
• Arrays.stream()
• BufferedReader.lines()
• CharSequence.chars()
• Pattern.splitAsStream()
How can I get a Stream?

6. 6 CONFIDENTIAL
Fluent and simple
txns.stream()
.filter(t ->t.getBuyer().getAge()>=65)
.map(Txn::getSeller)
.distinct()
.sort(comparing(Seller::getName))
.forEach(s -> System.out.println(s.getName());

7. 7 CONFIDENTIAL
java.util.function Package:
Predicate<T>
Determine if the input of type T matches some criteria
Consumer<T>
Accept a single input argument of type T, and return no result
Function<T, R>
Apply a function to the input type T, generating a result of type R
java.util.stream Package:
Collector<T, A, R>
Used to collect stream of elements of type T into single result of
type R
Collectors
Contains number of predefined Collectors
Functional interfaces

8. 8 CONFIDENTIAL
A lambda expression is an anonymous function
–  Argument list, a return type, and a body
(Object o) -> o.toString()
–  Method reference
Object::toString
–  Capture value from enclosing context
(Person p) ->p.getName().equals(name)
–  Type inference
p -> p.getName().equals(name)
–  Forget to use anonymous classes

You can now pass behavior as a data between your objects

#2 Lambdas

9. 9 CONFIDENTIAL
#3 Method reference
FileFilter x = (File f) -> f.canRead();
FileFilter x = File::canRead;
FileFilter x = new FileFilter() {
public boolean accept(File f) {
return f.canRead();
}
};

10. 10 CONFIDENTIAL
Since Java doesn’t have Function type on it’s own
Lambda’s type evaluated to some Functional
interface:

Runnable r = () -> { doSmth(); };
Callable c = () -> calcResult();
Comparator comp = (o1, o2) -> compare(o1, o2);

What’s your type?

11. 11 CONFIDENTIAL
Influence on existing classes
java.lang.Iterable#forEach()

java.util.Collection#stream()
java.util.Collection#parallelStream()

java.util.Comparator#comparing(…)
java.util.Comparator#thenComparing(…)
java.util.Comparator#reverse()
…

12. 12 CONFIDENTIAL
SHOW ME THE CODE
Lambdas and streams
TALK IS CHEAP

13. 13 CONFIDENTIAL
• Libraries need to evolve, or they stagnate
• Java preserves compatibility
• Multiple inheritance in Java?
• Default methods can reduce implementation
burden
• Resolution rules:
– Class wins over interface
– More specific subclass wins
– No 3
rd
rule
#4 Default methods

14. 14 CONFIDENTIAL
• Annoyed by NPEs?
• Should your method return null or throw
RuntimeException?
• Wondering how to implement SpecialCase
pattern?
• Inspired by functional programming and want to
build a method chain for NULL handling?

=> You are lucky with Java 8…

#5 Optional

15. 15 CONFIDENTIAL
#6 Date & Time API
• Replaces old ambiguous java.util.Date,
Calendar, TimeZone, DateFormat classes
with lots of deprecations
• More fluent/simple/clean API
• Immutable classes
• Using Java8 features including lambdas
• Precise separation of concepts

16. 16 CONFIDENTIAL
• LocalDate – a date only
• LocalTime – a time only
• LocalDateTime – date with time
• ZonedDateTime – date with time in time zone
• Period - date-based amount of time
• Duration - time-based amount of time
• And more…
Range of types

17. 17 CONFIDENTIAL
Time Zones
If you can avoid using TimeZones – do it!
If not – use ZonedDateAndTime!

18. 18 CONFIDENTIAL
• ZoneId – replacement for TimeZone class (e.g.
“Europe/London”, “Europe/Kiev”)
• ZoneOffset – representing offset from UTC time
• ZoneRules – behind the scenes class which
defines time zone rules
• ZonedDateTime – main date/time class which is
aware of time zones
TimeZone classes in Java 8

19. 19 CONFIDENTIAL
New API is very flexible because it based on number of
abstractions at it’s bottom:
Temporal – parent class for all date/time objects which
defines mutation operation for them such as plus/minus/
with
TemporalAdjuster – functional interface which responsible
for mutating Temporal objects
TemporalField – represents parts/fields of date/time
objects such as (DAY_OF_WEEK, MONTH, etc.)
TemporalUnit – represents type of date/time values such as
(MINUTES, DAYS, YEARS, etc.)
TemporalAmount – class which represents amount of time

Power of abstraction

20. 20 CONFIDENTIAL
SHOW ME THE CODE
Optional and Date and Time API
TALK IS CHEAP

21. 21 CONFIDENTIAL
• Whenever we think of using RWLock
• RWLock can cause starvation of readers
• RWLock is pessimistic on reads
• Read lock is optimistic
• Optimistic lock can be converted to pessimistic
lock if necessary
• Write locks are always pessimistic
#7 StampedLock

22. 22 CONFIDENTIAL
• [Java 5] When readers are given priority,
then writers might never be able to
complete
• [Java 6] But when writers are given
priority, readers might be starved

⇒ In Java 8 use StampedLock instead!


RWLock starvation

23. 23 CONFIDENTIAL
• Pros
– Has much better performance than
ReentrantReadWriteLock
– Latest versions do not suffer from starvation
of writers
• Cons
– Idioms are more difficult to get right than
with ReadWriteLock
– A small difference can make a big difference
in performance

StampedLock

24. 24 CONFIDENTIAL
How would you implement counter in
multithreaded environment?
• Dirty counters (silly)
• Synchronized (very slow)
• RWLock (slow)
• Volatile (only if you have 1 writer/updater)
• AtomicInteger (yes, before Java 8…)
⇒  LongAdder in Java 8!
#8 Concurrent Adders

25. 25 CONFIDENTIAL
WANT MORE?

26. 26 CONFIDENTIAL
9 Improved annotations
10 New file operations
11 Overflow operations
12 Base64 encoding
13 Nashorn JavaScript engine

27. 27 CONFIDENTIAL
• Process Termination
• Strong Random Generation
• Date.toInstant()
• Interface static methods
• Better Type Inference
• Parameter names support by compiler
• Parallel Arrays
• Nashorn CLI JavaScript interpriter
• Class dependency analyzer
However there are even more …

28. 28 CONFIDENTIAL
• https://www.google.com/?gws_rd=ssl
• https://github.com/RichardWarburton/java-8-
lambdas-exercises
• http://javaspecialists.eu/talks/jfokus13/
PhaserAndStampedLock.pdf
• http://www.javacodegeeks.com/2014/05/
java-8-features-tutorial.html
• http://blog.takipi.com/10-features-in-java-8-
you-havent-heard-of/
Resources

29. 29 CONFIDENTIAL
QUESTIONS?
Skype: oleg.tsalko
Twitter: @tsaltsol
THANK YOU