Java 8 Feature Preview
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Java 8 will include many new features including lambdas, default methods on interfaces, and a date/time API. Lambdas allow implementing functional interfaces with expression syntax rather than anonymous classes, and method references allow referring to methods without invoking them. Default methods allow adding new functionality to interfaces without breaking existing implementations. The new date/time API in JSR-310 provides improved date/time handling functionality.
![Method & Constructor References
• Provide a way to refer to a method / constructor
without invoking it
• Examples:
System::getProperty
"abc"::length
String::length
super::toString
ArrayList::new
int[]::new](https://image.slidesharecdn.com/java8featurepreview-170518143319/85/Java-8-Feature-Preview-32-320.jpg)
Java 8 Feature Preview
- 1. Java 8 Feature Preview Mostly about Lambdas
- 2. New Feature Overview • Roughly 50 new features • Worth mentioning – Concurrency updates (possible STM support) – JDBC 4.2 – leverage new data types via generic getter / setter methods (e.g. JSR 310 datatypes) – Launch JavaFX apps directly – http://openjdk.java.net/projects/jdk8/features has full details
- 4. Download JDK 8 • Lambda Support http://jdk8.java.net/lambda • No Lambda Support http://jdk8.java.net/download.html
- 5. IDE Support • Netbeans • IntelliJ • Eclipse is on the way (own compiler)
- 7. Before Compact Profiles (from Leader Summit –see http://www.hjug.org/present/iouc2013/2013-Java-Leaders-Summit-JavaSE.pdf)
- 8. Compact Profiles(from Leader Summit –see http://www.hjug.org/present/iouc2013/2013-Java-Leaders-Summit-JavaSE.pdf)
- 9. Nashorn • Replacement for Rhino JavaScript Engine • Collaboration between Oracle, IBM, and RedHat • Makes extensive use of invokedynamic • 20x faster than Rhino • Much smaller - can run on embedded devices • Open Sourced • Project Page: http://openjdk.java.net/projects/nashorn/
- 10. Metaspace • Bye bye PermGen • Holds class metadata • Introduced for convergence with JRockit • MetaSpace OoMEs can happen (when capped) • Initial size limited by amt of native memory • May want to update tuning flags
- 11. JSR 310 – java.time • All the Java Time classes are immutable and thread-safe. • Based on the ISO 8601 calendar system, the de facto world calendar following the proleptic Gregorian Rules. • Support for other calendar systems provided in java.time.calendar and java.time.temporal packages. • Besides classes for dates and times, the API also has classes for clocks, periods and durations, and enums for month and day-of-week.
- 12. Lambdas
- 13. Lambdas • A lambda expression is like a method: it provides a list of formal parameters and a body—an expression or block—expressed in terms of those parameters. • Expressions: s -> s.length() (int x, int y) -> x+y () -> 42
- 14. Lambdas • Blocks: (x, y, z) -> { if (true) return x; else { int result = y; for (int i = 1; i < z; i++) result *= i; return result; } }
- 15. Typical Use Cases • Anonymous classes (GUI listeners) • Runnables / Callables • Comparator • Apply operation to a collection via foreach method
- 16. SAM Type / Functional Interface • Single Abstract Method • A functional interface is an interface that has just one abstract method, and thus represents a single function contract. (Can have other methods with bodies) • Abstract classes may be considered in the future • The @FunctionalInterface annotation helps ensure the Functional Interface contract is honored • What happens when you have more than one abstract method & use @FunctionalInterface?
- 18. Effectively Final • For both lambda bodies and inner classes, local variables in the enclosing context can only be referenced if they are final or effectively final. • A variable is effectively final if its value is not reassigned after its initialization. • No longer need to litter code with final keyword
- 20. Convert Anonymous Class to Lambdafrom http://learnjavafx.typepad.com/weblog/2013/02/mary-had-a-little-%CE%BB.html // Anonymous inner class for event handling .onAction(new EventHandler<ActionEvent>() { @Override public void handle(ActionEvent e) { anim.playFromStart(); } })
- 21. Convert Anonymous Class to Lambda .onAction((ActionEvent) -> { anim.playFromStart(); } }) • The lambda type is inferred by the compiler as EventHandler<ActionEvent> because the onAction() method takes an object of type EventHandler<ActionEvent>.
- 22. Convert Anonymous Class to Lambda .onAction((e) -> { anim.playFromStart(); }) • The parameter in this lambda expression must be an ActionEvent, because that is the type specified by the handle() method of the EventHandler interface.
- 23. Convert Anonymous Class to Lambda .onAction(e -> { anim.playFromStart(); } ) • When a lambda expression has a single parameter and its type is inferred, the parentheses are not required
- 24. Convert Anonymous Class to Lambda .onAction(e -> anim.playFromStart()) • Because the block of code in our lambda expression contains only one statement, we can simplify it even further
- 26. forEach • forEach method available on Iterator & Map interfaces and their implementations • Allows for internal control of iteration of elements for possible parallel operation List<String> names = Arrays.asList("Alice", "Bob", "Charlie"); names.forEach(e -> { System.out.println(e); });
- 27. java.util.stream Classes to support functional-style operations on streams of values • Stream<T> - A sequence of elements supporting sequential and parallel bulk ops • Stream opened by calling – Collection.stream() – Collection.parallelStream() List<String> names = Arrays.asList("Bob", "Alice", "Charlie"); out(names.stream().filter(e -> e.length() > 4 ) .findFirst().get()); Returns “Alice”
- 28. java.util.stream • All other interfaces in stream package accessible through Stream interface • Collector<T,R> - A (possibly parallel) reduction operation that folds input elements into a mutable result container. • FlatMapper<T,U> - An operation that maps an element of type T to zero or more elements of type U.
- 29. java.util.function Functional interfaces provide target types for lambda expressions and method references. • Consumer<T> - Action to be performed on an object. • Function<T,R> - transform a T to an R. • Supplier<T> - A supplier of objects (e.g. factory). • Predicate<T> - Determines if the input object matches some criteria. • Unary/BinaryOperator<T> - An operation upon a single / two operand(s) yielding a result. • Bi(Consumer/Function/Predicate)<T,U(,R)> - Accepts two input arguments, yields result if specified
- 30. java.util • Spliterator<T> - A provider of element traversal operations for a possibly-parallel computation. • Optional<T> - A container object which may or may not contain a non-null value – Returned by Stream’s aggregate methods find*(), reduce(), min(), max() – Call get() to get the value it’s holding
- 31. Method & Constructor References • A method reference is used to refer to a (static or instance) method without invoking it • A constructor reference is similarly used to refer to a constructor without creating a new instance of the named class or array type. • Specified with the :: (double colon) operator
- 32. Method & Constructor References • Provide a way to refer to a method / constructor without invoking it • Examples: System::getProperty "abc"::length String::length super::toString ArrayList::new int[]::new
- 34. Convert call to Method Reference public class Test { static void foo(){} static { new Runnable() { @Override public void run() { Test.foo(); } }.run(); } }
- 35. Convert call to Method Reference public class Test { static void foo(){} static { ((Runnable) () -> Test.foo()).run(); } }
- 36. Convert call to Method Reference public class Test { static void foo(){} static { ((Runnable) Test::foo()).run(); } }
- 37. Use a Method Reference This bttnExit.setOnAction( (actionEvent) -> { try { stop(); } catch (Exception e) { // TODO: add error handling } }); Can be bttnExit.setOnAction(this::onExit ButtonClick); ... void onExitButtonClick() { try { stop(); } catch (Exception e) { // TODO: add error handling } }
- 38. Use a Constructor Reference interface Factory<T> { T make(); } Factory<List<String>> f1 = ArrayList::<String>new; • Every time make() is invoked, it will return a new ArrayList<String>
- 39. How many times have you heard
- 41. Whatever! • Method assigned to privileged interface: public class Main { public static class NotAutoCloseable { public void close() throws Exception { System.out.println("CLOSE"); } } public static void main(String... args) throws Exception { NotAutoCloseable nac = new NotAutoCloseable(); try (AutoCloseable ac = nac::close) { } } }
- 42. Interface Defender Methods • Interface methods with bodies • default keyword • More graceful API evolution • Interfaces have no state • Static methods not inherited • Can reference abstract method • Called “Extended Interfaces” if no abstract methods present
- 44. Super! • Extended Interfaces can extend other extended interfaces • Methods can be overridden • Can decorate parent definitions via super interface I1 { default void method1() {//do stuff}} interface I2 extends I1{ void default method1() { super.method1(); //do new stuff } }
- 46. Specify the Parent Interface interface D1 { default void meth1() {//do stuff}} interface D2 extends D1{ void default meth1() { super.method1(); //do new stuff}} interface D3 extends D1{ void default meth1() { super.method1(); //do new stuff}} interface D4 extends D2, D3{ void default meth1() { D2.super.method1(); //do new stuff}}
- 47. Design Patterns • Decorator (via super) • Template Method • Factory Method • Others?
- 48. New Java 8 Feature Overview • http://openjdk.java.net/projects/jdk8/features • http://java.dzone.com/articles/java-%E2%80%93-far-sight-look-jdk-8 Java 8 Maven Support • http://illegalargumentexception.blogspot.com/2012/08/java-lambda- support-in-java-8.html DateTime API • http://www.infoq.com/news/2013/02/java-time-api-jdk-8 • http://java.dzone.com/articles/introducing-new-date-and-time • http://geekmonkey.org/articles/24-a-new-date-and-time-api-for-jdk-8 Metaspace • http://java.dzone.com/articles/java-8-permgen-metaspace Nashorn • http://www.infoq.com/news/2012/11/Nashorn-proposal
- 49. Lambda JSR • http://jcp.org/en/jsr/detail?id=335 Java 8 Preview JDK • http://jdk8.java.net/lambda/ - lambda support • http://jdk8.java.net/download.html - no lambda support Articles on Lambdas • http://www.oraclejavamagazine-digital.com/javamagazine/20121112?pg=35#pg35 • http://www.angelikalanger.com/Conferences/Slides/jf12_LambdasInJava8-1.pdf • http://datumedge.blogspot.com/2012/06/java-8-lambdas.html • http://www.infoq.com/articles/java-8-vs-scala Presentations on Lambdas: • http://www.slideshare.net/ramonypp/java-8-project-lambda • http://www.slideshare.net/garthbrown/lambda-functions-in-java-8 • http://www.angelikalanger.com/Conferences/Slides/jf12_LambdasInJava8-1.pdf Lambda implementation mechanics: • http://cr.openjdk.java.net/~briangoetz/lambda/lambda-translation.html
- 50. Typical lambda use cases: • http://learnjavafx.typepad.com/weblog/2013/02/mary-had-a-little-%CE%BB.html • http://blueskyworkshop.com/topics/Java-Pages/lambda-expression-basics/ • http://java.dzone.com/articles/devoxx-2012-java-8-lambda-and Defender method paper: • http://cr.openjdk.java.net/~briangoetz/lambda/Defender%20Methods%20v4.pdf Method references (:: operator) • http://earthly-powers.blogspot.com/2012/07/java-8-lambda-and-method-references.html • http://doanduyhai.wordpress.com/2012/07/14/java-8-lambda-in-details-part-iii-method-and-constructor- referencing/ • http://www.beyondjava.net/blog/are-java-8-method-references-going-to-be-more-important-than-lambdas/ • http://www.lambdafaq.org/what-are-constructor-references/ Stream API: • http://cr.openjdk.java.net/~briangoetz/lambda/sotc3.html • http://aruld.info/java-8-this-aint-your-grandpas-java/ • http://java.dzone.com/articles/exciting-ideas-java-8-streams Sophisticated Lambda use case allowing for avoiding NPEs using Monads: • http://java.dzone.com/articles/no-more-excuses-use-null Functional programming in Java • http://code.google.com/p/functionaljava/ • http://shop.oreilly.com/product/0636920021667.do • http://apocalisp.wordpress.com/2008/06/18/parallel-strategies-and-the-callable-monad/