Dans cette présentation, je vous propose de découvrir ensemble ce qu’il est vraiment possible d’exprimer avec Java 8 et que peu ont testé. Est-il possible de limiter le nombre de sous-classes pour une classe ? Si on peut désormais mettre un comportement dans une interface, peut-on y mettre un état ? Live coding à l’appui, voici certaines des questions auxquelles nous allons essayer de répondre ou qu’on ne devrait jamais aborder. Code : https://gist.github.com/fsarradin/bea95af73651a57c1112

1. Java 8 eXperiment(s)
François Sarradin
Normandy JUG
20 octobre 2015

2. WARNING!!!

3. françois sarradin
• ippon technologies (ippon.fr)
• manager technique capitalisation
• extremist programmer, FP, agilité
• http://brownbaglunch.fr/
• twitter: @fsarradin
• blog: https://kerflyn.wordpress.com/

4. plan
1. héritage multiple
2. exception
3. pattern matching
et du live coding !!!

5. héritage multiple

6. objet = état + comportement

7. en java 8, on peut faire de l’héritage
multiple de comportement

9. mais peut-on faire de l’héritage
multiple d’état ?

10. un mail de Brian Goetz
Subject: Re: From virtual extension
methods to mixing
From: Brian Goetz <…@oracle.com>
Date: Mon, 9 Jul 2012 07:50:11 -0400
Cc: lambda-dev@openjdk.java.net
To: François Sarradin <…@gmail.com>
Please don't encourage techniques like
this. There are a zillion "clever" things you
can do in Java, but shouldn't. We knew it
wouldn’t be long before someone
suggested this, and we can't stop you. But
please, use your power for good, and not
for evil. Teach people to do it right, not to
abuse it.
But please, use your power for
good, and not for evil.
Please don't encourage
techniques like this.

12. un autre mail de Brian Goetz
Subject: Re: From virtual extension
methods to mixins
From: Brian Goetz <…@oracle.com>
Date: Tue, 10 Jul 2012 19:51:55 -0400
To: François Sarradin <…@gmail.com>
[…]
The bottom line is:
interfaces cannot be counted on to have
identity.
Which is a good thing, but can bite the
"clever" from behind :)

13. ce qu’il faut retenir

15. un mail de Brian Goetz
Subject: Re: From virtual extension
methods to mixing
From: Brian Goetz <…@oracle.com>
Date: Mon, 9 Jul 2012 07:50:11 -0400
Cc: lambda-dev@openjdk.java.net
To: François Sarradin <…@gmail.com>
Please don't encourage techniques like
this. There are a zillion "clever" things
you can do in Java, but shouldn't. We
knew it wouldn’t be long before someone
suggested this, and we can't stop you. But
please, use your power for good, and not
for evil. Teach people to do it right, not to
abuse it.
There are a zillion
"clever" things you
can do in Java, but
shouldn't.

16. exception

17. sun.misc.Unsafe est voué à
disparaître ?

19. checked exception non déclarée
Field f = Unsafe.class.getDeclaredField("theUnsafe");
f.setAccessible(true);
Unsafe unsafe = (Unsafe) f.get(null);
// throw undeclared checked exception
unsafe.throwException(new IOException());

20. alternative ?

21. ce qu’il faut retenir

22. limiter le nombre de sous-classes
public class Base {
private Base() {}
public static class Class1 extends Base {}
public static class Class2 extends Base {}
// ...
}

23. type checking
• limitation des sous-classes + generics => TDD
• TDD = type driven development
• ATTENTION !!! null interdit (checkstyle)

24. pyramide de test
UI
Intégration
Unitaire
Compilateur

25. pattern matching

26. Java 8 introduit la
programmation fonctionnelle

27. peut-on tenter d’y introduire le
pattern matching

28. pattern matching (scala)
myValue match {
case "hello" => println("hello world")
case i: Int => println("int: $i")
case Add(a, b) => println("$a + $b = ${a + b}")
case _ => println("what else!")
}

29. ce qu’il faut retenir

30. dsl en java
FirstWord firstWord(T t) { return new FirstWord(t); }
class FirstWord {
final T t;
FirstWord(T t) { this.t = t; }
FirstWord repeat(T t0) { return new FirstWord(t + t0); }
SecondWord secondWord(R r) { return new SecondWord(r); }
class SecondWord(R r) {
final R r;
SecondWord(R r) { this.r = r; }
S end() { return /* ... */; }
}
}

31. functional apis (beyond java 8)
• fugue (https://bitbucket.org/atlassian/fugue)
• functional java (http://www.functionaljava.org/)
• totallylazy (http://totallylazy.com/)
• jOOλ (https://github.com/jOOQ/jOOL)
• javaslang (http://javaslang.com/)
• cyclops (https://github.com/aol/cyclops)

32. conclusion

33. • optimisation en java (ne pas trop avec les concepts)
• limiter le nombres de sous-classes
• type driven development
• dsl en java

34. KEEP
CALM
AND
THANK
YOU