Java 8 to the rescue!?

Java 8 to the rescue!?JavaZone 2013

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torsdag 12. september 13

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RETURN OFTHE AVAJ

JAVA EIGHT


Fredrik Vraalsen

[email protected]

Dad, Java developer,

Scala enthusiast, sci-fi fan, photo geek

and Age of Conan assassin

@fredriv

© Fredrik Vraalsen 2008


mailto:[email protected]

mailto:[email protected]

Java 8 – what’s new?Lambdas, Extension Methods, SAMs, Streams, Method Handles, Oh My!

Nashorn JS engine

JSR-310: Date & time API

No more PermGen – where classloaders go to die

Compact profiles

...

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Java 8 – what’s new?Lambdas, Extension Methods, SAMs, Streams, Method Handles, Oh My!

Nashorn JS engine

JSR-310: Date & time API

No more PermGen – where classloaders go to die

Compact profiles

...

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Your MissionShould you choose to accept it

Sort a list of peopleby their names


Java 7List<Person> people = ...

Collections.sort(people);

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Java 7Collections.sort(people, new Comparator<Person>() {

});

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Java 7Collections.sort(people, new Comparator<Person>() { public int compare(Person x, Person y) {

}});

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Java 7Collections.sort(people, new Comparator<Person>() { public int compare(Person x, Person y) { return x.getName().compareTo(y.getName()); }});

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We are not amused



Java 7Collections.sort(people, new Comparator<Person>() { public int compare(Person x, Person y) { return x.getName().compareTo(y.getName()); }});

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Java 7Comparator<Person> byName = new Comparator<Person>() { public int compare(Person x, Person y) { return x.getName().compareTo(y.getName()); }};

Collections.sort(people, byName);

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sort(people, byName);Collections.

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sort(people, byName)


( , ;

Lisp?

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What about Java 8?© Fredrik Vraalsen 2012



sort(people, byName);

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people.sort(byName);

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Java 8

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java.util.List:

default void sort(Comparator<? super E> c)


Java 8

Defender MethodDefault Method

(Virtual) Extension Method20

java.util.List:

default void sort(Comparator<? super E> c)


Java 8java.util.List:

default void sort(Comparator<? super E> c) { }




Java 8java.util.List:

default void sort(Comparator<? super E> c) { Collections.sort(this, c); }




Extension methodExtend interfaces with new methods

Compatibility

Default implementation

Override

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C# extension methodsStatic methods

Cannot be overridden

One-size fits all solution

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Scala Traits“Interfaces on steroids”

Method implementations

Variables

Everything a class can have – except constructors

Can mix in multiple traits25


Ok, nice...What else?




Single Abstract Method

(SAM)27


Single Abstract MethodInterface with only one (non-default) method

Abstract class with only one abstract method

Sound familiar?

Pretty much every event listener, callback mechanism, ...

Can be replaced by a Lambda

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Lambda

Closure

Anonymous function29


SAMComparator<Person> byName = new Comparator<Person>() { public int compare(Person x, Person y) { return x.getName().compareTo(y.getName()); }};

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SAMComparator<Person> byName = new Comparator<Person>() { public int compare(Person x, Person y) { return x.getName().compareTo(y.getName()); }};

BodyReturn type

Parameter list

Method name

Type

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LambdaComparator<Person> byName = new Comparator<Person>() { public int compare(Person x, Person y) { return x.getName().compareTo(y.getName()); }};

BodyReturn type

Parameter list

Method name

Type

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LambdaComparator<Person> byName =

return x.getName().compareTo(y.getName()); };

BodyReturn type?

Parameter list

(Person x, Person y) -> {

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LambdaComparator<Person> byName = (Person x, Person y) ->

Parameter list

BodyReturn type?

x.getName().compareTo(y.getName());{

};return

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LambdaComparator<Person> byName =

Parameter list

BodyReturn type?

(x, y) -> x.getName().compareTo(y.getName());(Person x, Person y)

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Lambda – putting it togetherComparator<Person> byName = (x, y) -> x.getName().compareTo(y.getName());

people.sort(byName);

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Lambda – putting it together

people.sort((x, y) -> x.getName().compareTo(y.getName()));

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Lambda vs Java 7Collections.sort(people, new Comparator<Person>() { public int compare(Person x, Person y) { return x.getName().compareTo(y.getName()); }});

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Lambda vs Java 7Collections.sort(people, new Comparator<Person>() { public int compare(Person x, Person y) { return x.getName().compareTo(y.getName()); }});

vs

people.sort((x, y) -> x.getName().compareTo(y.getName()));

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Cool!

Now onwards...© Fredrik Vraalsen 2013


Method handlesReference to methods

Can be used in place of lambdas

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Method handlesclass Person { ... public int compareByName(Person other) { return name.compareTo(other.name); }}

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Comparator<Person> byName = (Person a, Person b) -> a.compareByName(b);

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Comparator<Person> byName = (a, b) -> a.compareByName(b);

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Comparator<Person> byName = Person::compareByName;

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Comparator<Person> byName = Person::compareByName;people.sort(byName);

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people.sort(Person::compareByName);

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So far, so good?Extension methods

Lambdas

Method handles

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So, what’s the catch?© Fredrik Vraalsen 2012


What’s wrong with using List::sort ?Modifies existing collection

Others may be using it?

Concurrency issues

Performance

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Streams



The old fashioned wayList<String> namesOfAdults = new ArrayList<>();

for (Person p : people) { if (p.getAge() >= 18) { namesOfAdults.add(p.getName()); }}

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StreamsStream<Person> stream = people.stream();

Stream<Person> adults = stream.filter(p -> p.getAge() >= 18);

Stream<String> namesOfAdults = adults.map(Person::getName);

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Streams – compose

Stream<String> namesOfAdults = people.stream(). filter(p -> p.getAge() >= 18). map(Person::getName);

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Streams – collect

List<String> namesOfAdults = people.stream(). filter(p -> p.getAge() >= 18). map(Person::getName). collect(Collectors.toList());

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Streams – collect

List<String> namesOfAdults = people.stream(). filter(p -> p.getAge() >= 18). map(Person::getName). collect(toList());

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Performance



Streams – performance

List<String> namesOfAdults = people.stream(). filter(p -> p.getAge() >= 18). map(Person::getName). collect(toList());

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Streams – performance

List<String> namesOfAdults = people.parallelStream(). filter(p -> p.getAge() >= 18). map(Person::getName). collect(toList());

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Scala FTW!

val namesOfAdults = people. filter(p => p.age >= 18). map(p => p.name)

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Scala FTW!

val namesOfAdults = people. filter(_.age >= 18). map(_.name)

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Scala FTW!

val namesOfAdults = people.filter(_.age >= 18).map(_.name)

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Scala FTW!

val namesOfAdults = people.par.filter(_.age >= 18).map(_.name).toList

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Streams – sorting

List<Person> sorted = people.stream(). sort(Person::compareByName). collect(Collectors.toList());

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Scala FTW 2!

val sorted = people.sortBy(_.name)

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Streams – pipelinesSource

collection, array, generator function, IO channel, ...

Intermediate operations (Stream-producing)

filter, map, ...

Terminal operations (value-producing)

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Streamsjava.util.stream

Create new results

Lazy

Parallelizable

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Ready tomake the jump!?



Play with it!Download from http://jdk8.java.net/download.html

Whitepapers at http://openjdk.java.net/projects/lambda/

FAQ http://www.lambdafaq.org/

Supported in IntelliJ IDEA 12 (and NetBeans nightlies?)

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http://jdk8.java.net/lambda/

http://jdk8.java.net/lambda/

http://openjdk.java.net/projects/lambda/

http://openjdk.java.net/projects/lambda/

http://www.lambdafaq.org/

http://www.lambdafaq.org/

Why use X instead?Java 8 not yet released (duh!)

March 2014?

Will be a long time before you can use it in enterprise dev!

Clojure and Scala available NOW! (JDK 1.5 and 1.6)

Important things are still missing

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What’s missing?Immutability

Value types

Immutable data structures

Lists, maps, sets, etc.

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What’s the big deal?Functional programming is all about values!

And transformations (functions) computing new values

Concurrency

Parallelism

Robustness

Testability

Better / higher abstractions

Less code, less bugs!73


Some help to be foundImmutable collections

Google Guava, FunctionalJava

Concurrency mechanisms

Akka (Actors, STM)

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What else is missing?Type inference

Pattern matching

For comprehensions

Named and default parameters

Properties

Implicit parameters / conversions

and much more...http://stackoverflow.com/questions/3844745/scala-advantages-after-java-having-closures/3844844#3844844 75


http://stackoverflow.com/questions/3844745/scala-advantages-after-java-having-closures/3844844#3844844

http://stackoverflow.com/questions/3844745/scala-advantages-after-java-having-closures/3844844#3844844

LambdaJ

Easier manipulation of collections and more, limited closure support

Google Guava

Lots of nice utility classes, some functional programming support

FunctionalJava

Most “pure” FP – but slow, separate collection hierarchy

Funcito

Simplify creation of functions from existing methods

Integrates with Guava, FunctionalJava, Jedi, ...

But I’m stuck in Java 6... Help!

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Questions?


[email protected] / @fredriv


Java 8 to the rescue!?

Technology

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