Java8

(x) -> x + x

Felipe Mamud

@ftmamud

Felipe Mamud

fmamud

fmamud

Agenda

• Environment lab

• Lambda expressions and Method references

• Functional Interfaces and Default Methods

• Java.util.function

• Stream API

• Repeating and Type Annotations

• New Java Date/Time API

• Java API additions

• Nashorn JS Engine

• Other stuffs

Environment lab

• Download JDK8 (currently 1.8.0-b132) http://www.oracle.com/technetwork/java/javase/downloads/index.html

• IDE Support for JDK 8 – Eclipse 4.4 Luna (M6 partially compliant)

– NetBeans 8

– IntelliJ IDEA 13.1

• Java™ Platform, Standard Edition 8 API Specification – http://docs.oracle.com/javase/8/docs/api/

Lambda expressions

• A lambda expression is an anonymous function (not 100% true for Java but lets assume it for time being)

• Syntax:

(arguments) -> (body)

• Following are some examples of Lambda expressions:

(int a, int b) -> { return a + b; } () -> System.out.println("Hello World"); (String s) -> { System.out.println(s); } () -> 42 () -> { return 3.1415; };

Lambda expressions

• Four important syntax rules: 1. Declaring the types of the parameters is optional;

2. Using parentheses around the parameter is optional if you have only one parameter;

3. Using curly braces is optional (unless you need multiple statements);

4. The return keyword is optional if you have a single expression that returns a value.

Lambda expressions

• Lambdas expressions are classified into two types:

– Capturing

• Lambdas are said to be “capturing” if they access a non-static variable or object that was defined outside of the lambda body. For example, this lambda captures the variable x: int x = 5; return y -> x + y;

Lambda expressions

• In order for this lambda declaration to be valid, the variables it captures must be “effectively final”. So, either they must be marked with the final modifier, or they must not be modified after they're assigned. – Non-capturing

• Is as opposed to capturing lambdas. A non-capturing lambda is generally going to be more efficient than a capturing one, because a non-capturing lambda only needs to be evaluated once.

Lambda expressions

• What lambdas don't do?

– Non-final variable capture: If a variable is assigned a new

value, it can't be used within a lambda. The “final” keyword is not required, but the variable must be “effectively final”. This code does not compile:

int count = 0; List<String> strings = Arrays.asList("a","b","c"); strings.forEach(s -> { count++; // error: can't modify the value of count });

Lambda expressions

– Exception transparency : If a checked exception may be thrown from inside a lambda, the functional interface must also declare that checked exception can be thrown. The exception is not propagated to the containing method. This code does not compile:

void appendAll(Iterable<String> values, Appendable out) throws IOException { // doesn't help with the error

values.forEach(s -> { out.append(s); // error: can't throw IOException here

// Consumer.accept(T) doesn't allow it

});

}

There are ways to work around this:

– define your own functional interface that extends Consumer and wrap the IOException through as a RuntimeException. (UncheckedIOException)

Lambda expressions

– Control flow (break, early return) : In the forEach examples above, a traditional continue is possible

by placing a “return;” statement within the lambda. However, there is no way to break out of the loop or return a value as the result of the containing method from within the lambda. For example:

final String secret = "foo";

boolean containsSecret(Iterable<String> values) { values.forEach(s -> {

if (secret.equals(s)) {

??? // want to end the loop and return true, but can't

}

});

}

Lambda expressions

– Examples:

//Old way:

new Thread(new Runnable() {

@Override

public void run() {

System.out.println("Hello from thread");

}

}).start();

//New way:

new Thread(

() -> System.out.println("Hello from thread")

).start();

Lambda expressions

– Examples:

//Old way:

button.addActionListener(new ActionListener() {

@Override

public void actionPerformed(ActionEvent e) {

System.out.println("From anonymous class");

}

});

//New way:

button.addActionListener( e ->

System.out.println("From lambda expressions!");

);

Lambda expressions

– Examples:

//Old way:

List<Integer> list = Arrays.asList(1, 2, 3, 4, 5, 6, 7);

for (Integer n : list) {

System.out.println(n);

}

//New way:

List<Integer> list = Arrays.asList(1, 2, 3, 4, 5, 6, 7);

list.forEach(n -> System.out.println(n));

//or we can use :: double colon operator

list.forEach(System.out::println);

Lambda expressions

• Is a literal method value that uses the colon double operator (::), corresponding to a lambda expression:

Method references

• Method references can point to: – Static methods; String::valueOf

– Instance methods; Object::toString

– Methods on instances; x::toString

– Constructors; TreeSet::new

Method references

Method reference Equivalent lambda expression String::valueOf x -> String.valueOf(x)

Object::toString x -> x.toString()

x::toString () -> x.toString()

ArrayList::new () -> new ArrayList<>()

• Example:

List<String> words = Arrays.asList("Biga", "Pisca", “Lopam"); words.forEach(System.out::println);

// java.lang.Iterable:

default void forEach(Consumer<? super T> action) //java.io.PrintStream:

public void println(String x)

Method references

Functional Interfaces

• a functional interface is defined as an interface with exactly one (non default) method.

• Example: @FunctionalInterface

public interface Runnable {

public abstract void run();

}

Functional Interfaces

• A new annotation, @FunctionalInterface, has been introduced.

• It can be placed on an interface to declare the intention of it being a functional interface.

• It will cause the interface to refuse to compile unless you've managed to make it a functional interface.

Functional Interfaces

• Each lambda expression can be implicitly assigned to one of the interface called Functional interface.

• Examples: new Thread(

() -> System.out.println("hello world") ).start();

Comparator<String> c = (a, b) ->

Integer.compare(a.length(), b.length());

Default methods

• Default methods are not abstract, so a functional interface can define as many default methods as it likes.

• Why we need Default Methods?

– R: Extensibility without breaking the implementor class.

Default methods

• Example:

public interface Iterable<T> { Iterator<T> iterator(); default void forEach(Consumer<? super T> action) { Objects.requireNonNull(action); for (T t : this) { action.accept(t); } } default Spliterator<T> spliterator() { return Spliterators.spliteratorUnknownSize(iterator(), 0); } }

Static methods on Interface

• Although not strictly related to default methods, the ability to add static methods to interfaces is a major change to the Java language. public interface Stream<T> extends BaseStream<T, Stream<T>> { ...

public static<T> Stream<T> of(T... values) { return Arrays.stream(values);

}

...

}

java.util.function

• Java 8 comes with several functional interfaces in package, java.util.function: – Function<T,R> - takes an object of type T and returns R; – Supplier<T> - just returns an object of type T; – Predicate<T> - returns a boolean value based on input of type T; – Consumer<T> - performs an action with given object of type T; – BiFunction - like Function but with two parameters; – BiConsumer - like Consumer but with two parameters; – BinaryOperator<T> - take two T's as input, return one T as output,

useful for "reduce" operations.

• It also comes with several corresponding interfaces for primitive types, such as: – IntConsumer – IntFunction<R> – IntPredicate – IntSupplier

Stream API

• New Java 8 Stream API provides utilities to support functional-style operations on streams of values.

• A stream is something like an iterator. The values “flow past” (analogy to a stream of water) and then they're gone. A stream can only be traversed once, then it's used up. Streams may also be infinite.

Stream API

• There are two types of Streams: – Sequential: The actions of a sequential stream occur

in serial fashion on one thread.

– Parallel: The actions of a parallel stream may be happening all at once on multiple threads.

• Usually, dealing with a stream will involve these steps: 1. Obtain a stream from some source; 2. Perform one or more intermediate operations; 3. Perform one terminal operation.

Stream API

• Threre are two operation types of Streams: – Intermediate: An intermediate operation keeps the

stream open and allows further operations to follow. – Lazy operations (e.g. filter, map, flatMap, peek, distinct, sorted, limit e substream)

– Terminal: A terminal operation must be the final operation invoked on a stream. Once a terminal operation is invoked, the stream is "consumed" and is no longer usable. (e.g. forEach, toArray, reduce, collect, min, max, count, anyMatch, allMatch, noneMatch, findFirst e findAny)

Stream API

• There are a couple more general properties of stream operations to consider: – Stateful: imposes some new property on the stream,

such as uniqueness of elements, or a maximum number of elements, or ensuring that the elements are consumed in sorted fashion. These are typically more expensive than stateless intermediate operations.

– Short-circuiting : allows processing of a stream to stop early without examining all the elements. This is an especially desirable property when dealing with infinite streams; if none of the operations being invoked on a stream are short-circuiting, then the code may never terminate.

Stream API

• Examples: int sumOfWeights = blocks.stream()

.filter(b -> b.getColor() == RED)

.mapToInt(b -> b.getWeight())

.sum();

Stream<Person> first4females = people.stream()

.peek(System.out::println)

.filter(p -> p.getGender().equals("F"))

.distinct()

.limit(4);

Repeating and Type Annotations

• Java 8 will allow annotations to be repeated. // the first of the month and every monday at 7am

@Schedule(dayOfMont = "first") @Schedule(dayOfWeek = "Monday", hour = 7) public void doGoblinInvasion() { ... }

• To do this there is a new method called

obj.getAnnotationsByType(Class annotationClass) on Class, Constructor, Method, etc. It returns an

array of all such annotations (or an empty array if there are none).

Repeating and Type Annotations

• In Java 8, annotations can also be applied to the use of types. This new ability is primarily aimed at supporting type-checking frameworks, such as Checker. These frameworks help find errors in your code at compile time.

// Class instance creation:

new @Interned RocketShip(); // Type cast: notNullString = (@NonNull String) str; // implements clause: class ImmutableSet<T> implements @Readonly Set<@Readonly T> { ... } // Thrown exception declaration:

void launchRocket() throws @Critical FireException { ... }

New Java Date/Time API

• Java 8 introduces a new Date/Time API that is safer, easier to read, and more comprehensive than the previous API.

• Java’s Calendar implementation has not changed much since it was first introduced and Joda-Time is widely regarded as a better replacement.

New Java Date/Time API

New Java Date/Time API

New Java Date/Time API

• Example:

// Old way

Calendar cal = Calendar.getInstance();

cal.set(Calendar.HOUR, cal.get(Calendar.HOUR) + 2);

// New Way LocalTime now = LocalTime.now();

LocalTime later = now.plus(2, ChronoUnit.HOURS);

New Java Date/Time API

• For timezone specific times you use ZonedDateTime.

// Leaving from San Francisco on July 20, 2013, at 7:30 p.m.

LocalDateTime leaving = LocalDateTime.of(2013, Month.JULY, 20, 19, 30);

ZoneId leavingZone = ZoneId.of("America/Los_Angeles");

ZonedDateTime departure = ZonedDateTime.of(leaving, leavingZone); // Flight is 10 hours and 50 minutes, or 650 minutes

ZoneId arrivingZone = ZoneId.of("Asia/Tokyo");

departure.withZoneSameInstant(arrivingZone).plusMinutes(650);

// Checks if the specified instant is in daylight savings.

if (arrivingZone.getRules().isDaylightSavings(arrival.toInstant()))

// LEAVING: Jul 20 2013 07:30 PM (America/Los_Angeles)

// ARRIVING: Jul 21 2013 10:20 PM (Asia/Tokyo)

(Asia/Tokyo standard time will be in effect.)

New Java Date/Time API

• Enums – Java 8 adds several enums, such as LocalDateTimeField and

LocalPeriodUnit, for expressing things like “days” and “hours” instead of the integer constants used in the Calendar API.

• Clock – The Clock can be used in conjunction with dates and times to help

build your tests. During production a normal Clock can be used, and a different one during tests. //To get the default clock, use the following: Clock clock = Clock.systemDefaultZone(); //The Clock can then be passed into factory methods; LocalTime time = LocalTime.now(clock);

New Java Date/Time API

• Working with time zones

ZoneId zone = ZoneId.systemDefault();

Clock clock = Clock.system(zone); // America/Sao_Paulo ZoneId zone = ZoneId.of("Europe/Berlin");

Clock clock = Clock.system(zone); // Europe/Berlin Set<String> availableZoneIds =

ZoneId.getAvailableZoneIds();

// [Asia/Aden, America/Cuiaba, Etc/GMT+9, Etc/GMT+8,...

New Java Date/Time API

• Doing calculations with times and dates Period days = Period.ofDays(5);

LocalTime time = LocalTime.now(); // 15:15:45.562

time.plus(5, ChronoUnit.DAYS);

// throws UnsupportedTemporalTypeException:

Unsupported unit: Days

time.plus(5, ChronoUnit.HOURS); // 20:15:45.562

New Java Date/Time API

• Period parse exploring:

Period parse = Period.parse("P5D"); // Period.ofDays(5)

– For example, the following are valid inputs:

"P2Y" // Period.ofYears(2) "P3M" // Period.ofMonths(3) "P4W" // Period.ofWeeks(4) "P1Y2M3D" // Period.of(1, 2, 3) "P1Y2M3W4D" // Period.of(1, 2, 25) "P-1Y2M" // Period.of(-1, 2, 0)

"-P1Y2M" // Period.of(-1, -2, 0)

New Java Date/Time API

• Fluent Date and Time API:

// calculate the payday LocalDate today = LocalDate.now();

today.with(TemporalAdjusters.lastDayOfMonth()).minusDays(2);

// immutable LocalDate dateOfBirth = LocalDate.of(2012, Month.MAY, 14); LocalDate firstBirthday = dateOfBirth.plusYears(1);

New Java Date/Time API

• Different display name types: DayOfWeek dow = DayOfWeek.MONDAY;

Locale locale = Locale.getDefault(); dow.getDisplayName(TextStyle.FULL, locale); // Monday

dow.getDisplayName(TextStyle.NARROW, locale); // M

dow.getDisplayName(TextStyle.SHORT, locale); // Mon //It is a valid year? MonthDay date = MonthDay.of(Month.FEBRUARY, 29); boolean

boolean validLeapYear = date.isValidYear(2010);

// Is leap year?

boolean validLeapYear = Year.of(2012).isLeap();

New Java Date/Time API

• Method naming conventions

New Java Date/Time API

• Interoperability with Legacy Code – Calendar.toInstant() converts the Calendar object to an

Instant.

– GregorianCalendar.toZonedDateTime() converts a GregorianCalendar instance to a ZonedDateTime.

– GregorianCalendar.from(ZonedDateTime) creates a GregorianCalendar object using the default locale from a ZonedDateTime instance.

– Date.from(Instant) creates a Date object from an Instant.

– Date.toInstant() converts a Date object to an Instant.

– TimeZone.toZoneId() converts a TimeZone object to a ZoneId.

Java API additions

• API additions – Collections

– Concurrency

– IO/NIO

– Reflection and annotation changes

– Other miscellaneous additions to java.lang, java.util, and elsewhere

http://www.techempower.com/blog/2013/03/26/everything-about-java-8/

• JDBC 4.2 (Rowset 1.2, REF_CURSOR support, etc.) http://docs.oracle.com/javase/8/docs/technotes/guides/jdbc/jdbc_42.html

Optional

• Java 8 comes with the Optional class in the java.util package for avoiding null return values (and thusNullPointerException).

• Tony Hoare, the invention of the null reference in 1965 for the ALGOL W programming language. He calls The Billion Dollar Mistake.

• Used in the Stream API or custom implementation

Optional

• Examples:

//Creating an instance of Optional using the factory method.

Optional<String> name = Optional.of("Puppy"); name.orElse("Bob")

//This fails with a NullPointerException.

Optional<String> someNull = Optional.of(null);

//This fails with a NoSuchElementException

Optional<String> someNull = Optional.ofNullable(null);

someNull.get();

Nashorn JS Engine

• Nashorn replaces Rhino as the default JavaScript

engine for the Oracle JVM. • Nashorn is much faster since it uses

the invokedynamic feature of the JVM. It also includes a command line tool (jjs).

• Java Platform, Standard Edition Nashorn User's Guide http://docs.oracle.com/javase/8/docs/technotes/guides/scripting/nashorn/

• Command line Nashorn: jjs script.js

Nashorn JS Engine

• Hello World:

var hello = function() {

print("Hello Nashorn!");

};

hello();

Nashorn JS Engine

• Examples: var data = [1, 2, 3, 4, 5, 6, 7, 8, 9, 10];

var filtered = data.filter(function(i) { return i % 2 == 0; }); print(filtered); var sumOfFiltered = filtered.reduce(function(acc, next) { return acc + next; }, 0); print(sumOfFiltered);

Nashorn JS Engine

• Examples:

var imports = new JavaImporter(java.util, java.io, java.nio.file);

with (imports) {

var paths = new LinkedList();

print(paths instanceof LinkedList); //true

paths.add(Paths.get("/"));

paths.add(Paths.get("/home"));

paths.add(Paths.get("/tmp"));

print(paths); // [/, /home, /tmp]

}

Nashorn JS Engine

• Call from Java Class:

ScriptEngineManager manager = new ScriptEngineManager();

ScriptEngine engine = manager.getEngineByName("nashorn");

Reader reader = new FileReader("/home/fmamud/script.js");

engine.eval(reader); // prints: 2,4,6,8,10

30

Other stuffs

• jdeps – In JDK 8, a new command-line tool, jdeps, is added

that developers can use to understand the static dependencies of their applications and libraries.

– Java Platform, Standard Edition Tools Reference http://docs.oracle.com/javase/8/docs/technotes/tools/unix/jdeps.html

– Usage: jdeps <options> <classes...>

where <classes> can be a pathname to a .class file, a directory, a JAR file, or a fully-qualified class name.

// monitoracao-v1.4b.jar.dot digraph "monitoracao-v1.4b.jar" { // Path: monitoracao-v1.4b.jar "br.com.bradesco.monitoracao" -> "java.io"; "br.com.bradesco.monitoracao" -> "java.lang"; "br.com.bradesco.monitoracao" -> "java.lang.reflect"; "br.com.bradesco.monitoracao" -> "java.net"; "br.com.bradesco.monitoracao" -> "java.sql"; "br.com.bradesco.monitoracao" -> "java.text"; "br.com.bradesco.monitoracao" -> "java.util"; "br.com.bradesco.monitoracao" -> "javax.naming"; "br.com.bradesco.monitoracao" -> "javax.sql"; "br.com.bradesco.monitoracao" -> "log.c.apis (BRS000A2.jar)"; "br.com.bradesco.monitoracao" -> "util.dataAccess.jdbc (not found)"; }

Other stuffs

– Example: > jdeps -dotoutput . monitoracao-v1.4b.jar BRS000A2.jar

// BRS000A2.jar.dot digraph "BRS000A2.jar" { // Path: BRS000A2.jar "log.c.apis" -> "java.io"; "log.c.apis" -> "java.lang"; "log.c.apis" -> "java.net"; "log.c.apis" -> "java.sql"; "log.c.apis" -> "java.util"; "log.c.apis" -> "javax.naming"; "log.c.apis" -> "javax.sql"; }

//summary.dot digraph "summary" { "monitoracao-v1.4b.jar“ -> "BRS000A2.jar"; "monitoracao-v1.4b.jar“ -> "not found"; "monitoracao-v1.4b.jar“ -> "rt.jar"; "BRS000A2.jar“ -> "rt.jar"; }

Other stuffs

• No More Permanent Generation – Most allocations for the class metadata are now allocated

out of native memory. This means that you won’t have to set the “XX:PermSize” options anymore (they don’t exist).

– This also means that you will get a “java.lang.OutOfMemoryError: Metadata space” error message instead of “java.lang.OutOfMemoryError: Permgen space” when you run out of memory.

– This is part of the convergence of the Oracle JRockit and HotSpot JVMs.

Other stuffs

• Compact profiles – Java 8 will define subset profiles of

the Java SE platform specification that developers can use to deploy. Compact1 have less than 14MB; Compact2 is about 18MB; Compact3 is about 21MB.

For reference, the latest Java 7u21 SE Embedded

ARMv5/Linux environment requires 45MB.

• An Introduction to Java 8 Compact Profiles – https://blogs.oracle.com/jtc/entry/a_first_look_at_compact

Useful links

• What's New in JDK 8 http://www.oracle.com/technetwork/java/javase/8-whats-new-2157071.html

• JDK 8 Adoption Guide http://www.oracle.com/technetwork/java/javase/jdk8-adoption-guide-2157601.html

• Compatibility Guide for JDK 8 http://www.oracle.com/technetwork/java/javase/8-compatibility-guide-2156366.html

References

• Everything about Java 8 http://www.techempower.com/blog/2013/03/26/everything-about-java-8/

• Java 8 Lambda Expressions Tutorial With Examples http://viralpatel.net/blogs/lambda-expressions-java-tutorial/

• Java SE 8: Lambda Quick Start http://www.oracle.com/webfolder/technetwork/tutorials/obe/java/Lambda-QuickStart/index.html

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