This document provides an overview and comparison of new features in Java 8 and Scala, with a focus on lambda expressions. It notes that Java 8 adds lambda expressions and default interface methods to provide more expressiveness and concurrency capabilities similar to functional programming languages like Scala. The document discusses how lambda expressions improve on anonymous inner classes in Java and demonstrates various lambda expression forms in both Java 8 and Scala. It also highlights new Java 8 features like method references and parallel streams for easier parallel programming.

1. Scala
vs
Java 8
List("Sarradin", "Armand")
.map("François " + _)
2012-12-20

2. François Sarradin
Xebia
Twitter: @fsarradin
Blog: http://kerflyn.wordpress.com/
François Armand
Normation
Twitter: @fanf42

3. Dernier PSUG
Avant la fin du monde

4. Pourquoi cette présentation
(au PSUG ?)
!!! DISCLAIMER !!!
● Pas de troll
● Ni monade, ni typeclass
● Pas de conflit d'intérêt
● Vous avez le droit de parler aux chauffeurs

5. À venir
● Présentation de concepts
● Faire des trucs avec les concepts
● Parler des concepts

6. Java 8

7. Plus de Processeurs

8. Plus d'Expressivité
Plus de Lisibilité
结果 汉字 = new 物().処理();
vs.
fact n = product [1..n]
Is it all Chinese to you?

9. FP & Concurrence
C++
C# / F#
Clojure Guava

10. (Anonymous) Inner Class
Une Solution λ
adults = Iterables.filter(persons,
new Predicate<Person>() {
@Override
public boolean apply(Person person) {
return person.getAge() >= 18;
}
}); // Java + Guava

11. (Anonymous) Inner Class
Une Solution λ
adults = Iterables.filter(persons,
new Predicate<Person>() {
@Override
public boolean apply(Person person) {
return person.getAge() >= 18;
}
}); // Java + Guava

12. (Anonymous) Inner Class
(Pas Vraiment) Une Solution λ
● "The pain of anonymous inner classes makes us roll
our eyes in the back of our heads every day." (a wise
Oracle's client - 01/2011)
Average length of Java one-liner is 21 line!
@DEVOPS_BORAT - 12/09/2011

13. λ Project Date and Time
(JSR 335) API (JSR 310) Project Coin
Nashorn
(JSR ?)
Performance Productivité
Annotation on
Types (JSR 308)
Java 8
(JSR 337)
Project Jigsaw Modularité
(JSR ?) Java 9

14. [New]
Method Reference [New] Interface Method
[New] T::m T::new default void m()...
x -> f(x) obj::m
Virtual
λ Expression Change in Extension
Property
Inheritance Method
Type Inference [New]
Engine Static Method in
Enhancement Interface
λ Project
(JSR 335)
Collection
[New]
API Extension Parallel Collections

15. Une Lambda Expression
(int x, int y) -> { return x + y; }

16. Une Lambda Expression
(x, y) -> { return x + y; }

17. Une Lambda Expression
(int x, int y) -> x + y
Scala
(x:Int, y:Int) => x + y

18. Une Lambda Expression
(x, y) -> x + y
Scala
(x, y) => x + y

19. D'autres formes de λ
x -> 2 * x
() -> 42
m -> {
m.put("France", "Paris");
m.put("UK", "London");
m.put("USA", "Washington");
}

20. Inner Class vs λ Solution
Iterables.filter(persons,
new Predicate<Person>() {
@Override
public boolean apply(Person p) {
return p.getAge() >= 18;
}
}); // Java 5-7 + Guava
Iterables.filter(persons, // Java 8 + Guava
person -> person.getAge() >= 18);

22. λ = SAM
(Single Abstract Method)
● Indépendant du type
● Une et une seule méthode abstraite
● Fonctionne avec
○ Runnable, Callable, Comparator
○ JDK's function API, Guava API
○ types persos, ...

23. λ et variables externes
int x = 1; => Implicitement final
y -> y + x;
x = 2;

24. Method Reference
String::valueOf
// like: v -> String.valueOf(v)
String::new
// like: v -> new String(v)
myBigDecimal::add
// like: (n) -> myBigDecimal.add(n)
Arrays.sort(myInts, Integer::compare)

25. Virtual Extension Method
(VEM)
interface Message {
default String getMessage() {
return "Look Ma'! Interface with code!";
}
}

27. VEM : Dangereux ?
● Brian Goetz : NON
○ Héritage de comportement uniquement
● François Sarradin : OUI O_O'
○ Article : "Java 8: Now You Have Mixins?"
○ (Voir les kata)

28. Faire évoluer les APIs
● "APIs need a mechanism for evolving, or they will
become increasingly constraining to use, and replacing
them is expensive." (Brian Goetz - 07/2012)

29. Parallel Computing
Aussi simple que 1-2-3 ?
myCollection.stream()
.filter(x -> ...)
.map(x -> ...)
.reduce((x, y) -> ...) // sequential
myCollection.parallel()
.filter(x -> ...)
.map(x -> ...)
.reduce((x, y) -> ...) // parallel

30. The Dream Team ;)
photo: @crazybob

31. Java 8
Sites Web
Java SE 8 Early Access (with lambda)
http://jdk8.java.net/lambda/
Mercurial repo
http://hg.openjdk.java.net/lambda/lambda
Mailing List
mailto:lambda-dev@openjdk.java.net
http://mail.openjdk.java.net/pipermail/lambda-dev/

32. Et maintenant,
scéance de code
in vivo...

33. Questions ?
● Adoption de Java 8 / Scala ?
● Debuggage ?
● Utilisation des Lambda Java 8 en Scala ?