Java 8 features
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This document discusses new features in Java 8 including stream API, lambdas, default methods, optional values, date and time API, stamped locks, concurrent adders, improved annotations, new file operations, overflow operations, and the Nashorn JavaScript engine. It provides code examples and explanations of how to use these new features in Java 8.
![22CONFIDENTIAL
• [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](https://image.slidesharecdn.com/java8features-150615070554-lva1-app6891/85/Java-8-features-22-320.jpg)
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Java 8 features
- 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. 3CONFIDENTIAL • 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. 4CONFIDENTIAL • 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. 5CONFIDENTIAL • Collection.stream() • IntStream.range() • Stream.of() • Arrays.stream() • BufferedReader.lines() • CharSequence.chars() • Pattern.splitAsStream() How can I get a Stream?
- 6. 6CONFIDENTIAL 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. 7CONFIDENTIAL 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. 8CONFIDENTIAL 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. 9CONFIDENTIAL #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. 10CONFIDENTIAL 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. 11CONFIDENTIAL 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. 12CONFIDENTIAL SHOW ME THE CODE Lambdas and streams TALK IS CHEAP
- 13. 13CONFIDENTIAL • 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 3rd rule #4 Default methods
- 14. 14CONFIDENTIAL • 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. 15CONFIDENTIAL #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. 16CONFIDENTIAL • 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. 17CONFIDENTIAL Time Zones If you can avoid using TimeZones – do it! If not – use ZonedDateAndTime!
- 18. 18CONFIDENTIAL • 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. 19CONFIDENTIAL 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. 20CONFIDENTIAL SHOW ME THE CODE Optional and Date and Time API TALK IS CHEAP
- 21. 21CONFIDENTIAL • 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. 22CONFIDENTIAL • [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. 23CONFIDENTIAL • 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. 24CONFIDENTIAL 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
- 26. 26CONFIDENTIAL 9 Improved annotations 10 New file operations 11 Overflow operations 12 Base64 encoding 13 Nashorn JavaScript engine
- 27. 27CONFIDENTIAL • 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. 28CONFIDENTIAL • 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