New Features in JDK 8

Ivan St. IvanovDmitry AlexandrovMartin Toshev

Agenda

• Lambda Expressions

• Other New Features in JDK 8

• JEPs and JDK 9 Development

Lambda Expressions

Lambdas

• Lambdas bring anonymous function types in Java (JSR 335):

• Example:

(x,y) -> x + y

(parameters) -> {body}

Lambdas

• Lambdas bring anonymous function types in Java

• Example:

… well … Groovy (a superset of java) already provides this …

(x,y) -> x + y

(parameters) -> {body}

Lambdas

• Lambdas can be used in place of functional interfaces (interfaces with just one method such as Runnable)

• Example:new Thread(new Runnable() {

@Overridepublic void run() {

System.out.println("It runs !"); }}).start();

new Thread(() -> { System.out.println("It runs !"); }).start();

Lambdas

• Examples of such functional interfaces:

java.lang.Runnable -> run() java.util.concurrent.Callable -> call() java.security.PrivilegedAction -> run() java.util.Comparator -> compare(T o1, T o2) java.awt.event.ActionListener ->

actionPerformed (ActionEvent e) java.lang.Iterable ->

forEach(Consumer<? super T> action)

Lambdas

java.lang.Iterable -> forEach(Consumer<? super T> action) ?!?

Isn't this breaking backward compatibility ?!?

Lambdas

java.lang.Iterable -> forEach(Consumer<? super T> action) ?!?

Isn't this breaking compatibility ?!?

No - because forEach is an extension method.

Lambdas

Extension methods provide a mechanism for extending an existing interface without breaking backward compatibility.

public interface Iterable<T> {

default void forEach(Consumer<? super T> action) { Objects.requireNonNull(action); for (T t : this) { action.accept(t); } }}

Lambdas

• This essentially means that lambdas can be used to replace all functional interfaces used in a gazillion of libraries

• Moreover lambdas increase performance when used instead of anonymous inner classes because they are implemented with the invokedynamic instruction

• In this regard many of the standard JDK class are being refactored to use lambdas

Lambdas

• Additional functional interfaces are provided by the java.util.function package for use by lambdas such as:o Predicate<T> - one method with param of type T and

boolean return typeo Consumer<T> - one method with param T and no

return typeo Function<T, R> - one method with param T and return

type Ro Supplier<T> - one method with no params and return type T

Stream API

• Databases and other programming languages allow us to specify aggregate operations explicitly

• The streams API provides this mechanism in the Java platform

• The notion of streams is derived from functional programming languages

Stream API

• The stream API makes use of lambdas and extension methods

• Streams can be applied on collections, arrays, IO streams and generator functions

Stream API

• Streams can be finite or infinite

• Streams can apply intermediate functions on the data that produce another stream (e.g. map, reduce)

Stream API

java.util.stream.Stream<T> collection.stream();java.util.stream.Stream<T> collection.parallelStream();Useful methods:

o filter(Predicate), map(Function), reduce(BinaryOperator), collect()

o sum(), min(), max(), count()o anyMatch(), allMatch(), forEach(),

Stream internals

• Stream operations are composed into a pipeline

• Streams are lazy: computation is performed when the terminal operation is invoked

int sum = widgets.stream() .filter(w -> w.getColor() == RED) .mapToInt(w -> w.getWeight()) .sum();

Method references

• Intended to be used in lambda expressions, preventing unnecessary boilerplate

• Example:

• Lambda parameter list and return type must match the signature of the method

books.stream().map(b -> b.getTitle()) books.stream().map(Book::getTitle)

Method references – static methods

public class Printers { public static void print(String s) {...} }

Arrays.asList("a", "b", "c").forEach(Printers::print)

Method references – instance methods (1)

public class Document { public String getPageContent(int pageNumber) { return this.pages.get(pageNumber).getContent(); }}

public static void printPages(Document doc, int[] pageNumbers) { Arrays.stream(pageNumbers) .map(doc::getPageContent) .forEach(Printers::print); }

Method references – instance methods (2)

public class Document { public String getPageContent(int pageNumber) { return this.pages.get(pageNumber).getContent(); }}

public static void printDocuments(List<Page> pages) { pages.stream() .map(Page::getContent) .forEach(Printers::print); }

Method references – constructors

public static Stream<Page> createPagesFrom(Stream<String> contents) { return contents.map(Page::new). }

Lambda Expressions:Hands-On-Lab

Lambdas Hands-on-Lab:Overview

• Environment setup

• Concept

• Task categories

Lambdas Hands-on-Lab:Environment Setup

• Download and install OpenJDK 8 early access

build from https://jdk8.java.net/lambda/ (… or build yours from the OpenJDK repo)

Lambdas Hands-on-Lab:Environment Setup

• Download and install an IDE:

o Eclipsehttp://www.oracle.com/technetwork/articles/java/lambda-1984522.html(for Eclipse 4.3: Start IDE -> Install New Software)http://build.eclipse.org/eclipse/builds/4P/siteDir/updates/4.3-P-builds

o IntelliJ IDEA CEhttp://www.jetbrains.com/idea/free_java_ide.html

Lambdas Hands-on-Lab:Environment Setup

• Get the sources:

or download

• Import the sources as Maven projects in the IDE• Set the Java 8 profile (source compatibility level)• Check if the sources compile and that you are able to run

ConfigureYourLambdaBuildOfJdk

git clone https://github.com/AdoptOpenJDK/lambda-tutorial

http://dmitryalexandrov.net/lambda.zip

Lambdas Hands-on-Lab:Concept

• We have several classes and tests for them

• Find “// your code here” and write the code !

• Run the tests. Try to make them green!(… read the comments.. They are useful !)

Lambdas Hands-on-Lab:Task Categories

• Internal vs External Iteration

• Filtering and Collecting

• Mapping

• Method References

Lambdas Hands-on-Lab:Internal vs External Iteration

Java 8 (Internal)

myShapes.forEach(shape -> shape.setColor(RED));

Java 7 (External)

for (Shape shape: myShapes) { shape.setColor(RED);

}

Lambdas Hands-on-Lab:Filtering and Collecting

Java8otherThings.stream()

.filter(s -> satisfiesSomeCondition(s))

.collect(Collectors.toList());

Java7for (String s: otherThings) {

if (satisfiesSomeCondition(s)) { things.add(s);

}}

Lambdas Hands-on-Lab:Mapping

Java8mixedCaseStrings.stream()

.map(s -> s.toUpperCase()) .collect(Collectors.toList());

Java7List<String> upperCaseStrings = new ArrayList<>();for (String s: mixedCaseStrings) {

upperCaseStrings.add(s.toUpperCase());}

Lambdas Hands-on-Lab:Mapping

Using a lambda expression:

myStrings.map(s -> s.toUpperCase());

Using a method reference:

myStrings.map(String::toUpperCase);

Can be used with:• Static methods belonging to a particular class (<class>::<staticMethod>)• Instance methods bound to a particular object instance (<obj> ::

<instanceMethod>)• Instance methods bound to a particular class (<class> :: <instanceMethod>)• Constructor belonging to a particular class (<class> :: new)

Lambdas Hands-on-Lab:Default Methods

Java 8

public interface A { default void foo(){ System.out.println("Calling A.foo()"); }}

public class Clazz implements A {}

Clazz clazz = new Clazz();clazz.foo(); // Calling A.foo()

Lambdas Hands-on-Lab:Default Methods

Java 8

public class Clazz2 implements A { @Override public void foo(){ System.out.println("Calling A.foo()"); }}

Clazz2 clazz2 = new Clazz2();clazz2.foo(); // Calling A.foo()

Lambdas Hands-on-Lab:Let's have some fun

Lambdas Hands-on-Lab:Hints

Examples:1. (int x, int y) -> x + y2. (x, y) -> x - y3. () -> 42 4. (String s) -> System.out.println(s)5. x -> 2 * x6. c -> { int s = c.size(); c.clear(); return s; }7. myShapes.forEach(shape -> shape.setColor(RED));8. otherThings.stream().filter(s -> satisfiesSomeCondition(s)).collect(Collectors.toList());9. mixedCaseStrings.stream().map(s -> s.toUpperCase()).collect(Collectors.toList());10. myStrings.map(String::toUpperCase); 11. public interface A { default void foo(){ System.out.println("Calling A.foo()");} }

The basic syntax of a lambda is either (parameters) -> expressionor (parameters) -> { statements; }

Other New Features in JDK 8

Date and Time API (JSR 310)

• Provides a new date, time and calendar API for the Java SE platform

• Examples:Clock clock = Clock.systemUTC();ZoneId zone = ZoneId.systemDefault();ZoneId customZone = ZoneId.of("Europe/Berlin");Clock customClock = Clock.system(customZone);DateTimeFormatter formatter = DateTimeFormatter.

ofPattern("MM-DD-YYYY");LocalDate date = LocalDate.now();String formattedDate = date.format(formatter);System.out.println(formattedDate);

Nashorn (via JSR 223)

• Nashorn is a JavaScript engine developed in the Java language

• A command line tool (jjs) for running javascript without using Java is also provided

Nashorn (via JSR 223)

• Nashorn is a JavaScript engine developed in the Java language

• A command line tool (jjs) for running javascript without using Java is also provided

• … well … JDK 6 is already shipped with Mozilla's Rhino JavaScript engine but is slower …

Nashorn (via JSR 223)

• Example (calling JavaScript from Java):

ScriptEngineManager m = new ScriptEngineManager();ScriptEngine nashorn = m.getEngineByName("nashorn");try {

nashorn.eval("print('Hello, world')");} catch (ScriptException e) {}

Nashorn (via JSR 223)

• Example (calling Java from JavaScript):

var ExampleType = Java.type("com.sample.Example");var example = new ExampleType("arg");print(example.method())

Parameter Names (JEP 118)

• Parameter names for method/constructor parameters can be retrieved at runtime via reflection

Method method = …Parameter param = method.getParameters()[0];System.out.println(param.getName());

Annotation on Java Types (JSR 308, JEP 104)

• Extend the set of annotatable locations in the syntax of the Java programming language

• Allow type checkers in the form of compiler plug-ins to provide stronger type checking

• Sample annotations: @notnull, @readonly

• Enhancements to JSR 269 (Pluggable Annotation Processing API)

Repeating Annotations(JEP 120)

• Change the Java programming language to allow multiple annotations with the same type on a single program element

Base64 Encoding/Decoding(JEP 135)

• Defines a standard API for Base64 encoding and decoding:java.util.Base64.Encoderjava.util.Base64.Decoder

Concurrency Updates(JEP 155)

• Scalable updatable variables (for frequent updates from multiple threads) are part of the concurrency updates:java.util.concurrent.atomic.DoubleAccumulatorjava.util.concurrent.atomic.DoubleAdderjava.util.concurrent.atomic.LongAccumulatorjava.util.concurrent.atomic.LongAdder

Compact Profiles(JEP 161)

• Defines a few subset Profiles of the Java SE Platform Specification so that applications that do not require the entire Platform can be deployed and run on small devices.

• Currently three profiles: o compact1o compact2o compact3

Other

• Prepare for modularization (JEP 162) - changes and deprecation of APIs to prepare for the modularization of the platform as undertaken by project Jigsaw

• Permanent generation space removed - objects from this space such as class metadata, static variables and interned strings moved to heap space

(improved convergence between OpenJDK and Oracle's JRockit)

Some books

JEPs and JDK 9 Development

JEPs and JDK 9 Development

So lets see what JEPs are left for JDK 9 ->http://openjdk.java.net/jeps/

Q&A

References

OpenJDK 8 early access buildshttps://jdk8.java.net/

Oracle JDK 8 early access buildshttp://www.oracle.com/technetwork/java/javase/downloads/ea-jsp-142245.html

Eclipse with JDK 8 supporthttps://wiki.eclipse.org/JDT_Core/Java8

References

OpenJDK mercurial repositorieshttp://hg.openjdk.java.net/

OpenJDK 9 build instructionshttp://hg.openjdk.java.net/jdk9/jdk9/raw-file/tip/README-builds.html

JSR 337: Java SE 8 (Early Draft Review Specification)http://cr.openjdk.java.net/~mr/se/8/java-se-8-edr-spec.html

References

Lambda tutorialhttps://github.com/AdoptOpenJDK/lambda-tutorial

State of the Lambdahttp://cr.openjdk.java.net/~briangoetz/lambda/lambda-state-final.html

Lambda FAQhttp://www.lambdafaq.org/

References

Java SE tutorials: Lambda Expressionshttp://docs.oracle.com/javase/tutorial/java/javaOO/lambdaexpressions.html

Lambda Quick Start Guidehttp://www.oracle.com/webfolder/technetwork/tutorials/obe/java/Lambda-QuickStart/index.html

Java Enhancement Proposalshttp://openjdk.java.net/jeps