New Java version from the functional programmer perspective. Talk I gave @ Informatica. Covers most major Java 8 additions including default methods, lambda expressions, PermGen removal, stream api, etc. Slides online: http://hakutaku.me/j8 Code examples: https://github.com/Oregu/j8

1. JAVA 8
HIPSTER SLIDES
NEW JAVA VERSION FROM FUNCTIONAL PROGRAMMER PERSPECTIVE
Createdby /OlegProphet @oregu_desu

2. JAVA 8
03/18/2014
Lastupdate: 5
Unofficialtagline:
YOU CAN BE HIPSTER TOO.

3. FEATURES
Mixins, akadefaultmethods
Collection goodies
More type inference
ProjectLambda
Streams
No Permgen. No OOME: permgen space errors*

4. DEFAULT METHODS
Known as Defender Methods
Implementation methods in interfaces
Poor man's Mixins
Multiple inheritance
(With ambiguityresolvingmechanism!)
Reduce abstractclasses
Utilitymethods
“Addingamethod to an interface is notnow asource-
compatible change”

5. DEFAULT METHODS EXAMPLE
publicinterfaceSized{
defaultbooleanisEmpty(){
returnsize()==0;
}
intsize();
}
À-LA MIXINS EXAMPLE
classVeryFastCarextendsACarimplementsIFastCar,IFastSteerCar{}
classVerySlowCarextendsACarimplementsISlowCar,ISlowSteerCar{}
//Evenbetterwouldbe(youcaninScala)
ICarcar=newACar()withISlowCar,IFastSteerCar;

6. MORE POWER TO INTERFACES
Finally!Define static methods right in the interfaces.
How thatmakes you feel, huh?
Remove your Collections, Arrays, Paths now.

7. COLLECTION GOODIES
MAPS:
getOrDefault(K, V) m/
putIfAbsent(K, V)
replace(K, Vnew)
replace(K, Vold, Vnew)
compute(K, BiFunction) *
computeIfAbsent(K, Function) *
computeIfPresent(K, BiFunction) *
merge(T, V, BiFunction) *
Reduce your boilerplate.

8. COLLECTION GOODIES
Setand Listdidn'tchange interface much, butlet's lookup
Collection and Iterable.
spliterator() *
removeIf(Predicate) *
stream() *
parallelStream() *
(Iterable).forEach(Consumer) *
*We'llgetto them in amoment.

9. DATE/TIME GOODIES
Since mutabilityis evil, we replaced java.util.Date class with a
bunch of immutable java.time.*classes!
“Allthe classes are immutable and thread-safe.”

10. TYPE INFERENCE
JAVA 7
voidprocessStringLst(List<String>l){...}
Lst.processStringLst(List.<String>empty());
JAVA 8
Lst.processStringLst(List.empty());
BUT STILL
Strings=Lst.<String>singleton().head();
Meh…

11. TYPE INFERENCE
More we'llsee in lambdaslides

12. LAMBDA SLIDES
() → ​{}

13. () → ​{}
ProjectLambda(JSR#335)
Initiated in December 2009 as Straw-Man proposal
Loooongawaited
Fullclass support
Notasyntactic sugar for an anonymous inner class
Even though itcan appear so.
Theyare noteven objects.

14. WITHOUT () → ​{}
List<String>names=newArrayList<String>();
for(inti=0;i<fields.size();i++){
Fieldfld=fields.get(i);
names.add(fld.getName());
}
for(inti=0;i<names.size();i++){
Stringname=names.get(i);
System.out.println(name);
}

15. () → ​{}
names=fields.stream().map(Field::getName).collect(toList());
names.forEach(System.out::println);

16. () → ​{}
names.map((Strings)->{returns.length();});
We know it's acollection of strings!
names.map((s)->s.length());
That's notaLISP!Who likes parentheses anyway?
names.map(s->s.length());
Can I have amethod reference, please?
names.map(String::length);
Thank you, Java8.

17. () → ​{}
METHOD REFERENCES
Object::toString
Field::create
Field::new
this::processField
a::process (ais some objectin scope)

18. MORE () → {} EXAMPLES
//Groupemployeesbydepartment
Map<Department,List<Employee>>byDept
=employees.stream().collect(groupingBy(Employee::getDepartment));
//Partitionstudentsintopassingandfailing
Map<Boolean,List<Student>>passingFailing
=students.stream().collect(partitioningBy(
s->s.getGrade()>=PASS_THRESHOLD));
//Classifypeoplebystateandcity
Map<String,Map<String,List<Person>>>peopleByStateAndCity
=personStream.collect(groupingBy(Person::getState,
groupingBy(Person::getCity)))

19. FUNCTIONAL INTERFACES
@FunctionalInterface
publicinterfaceFunction<T,R>{
Rapply(Tt);
}
Function<String,String>m=s->s.toUpperCase();
Function<String,Integer>f=String::length;
Functiong=f.andThen(Integer::reverse);
Functionid=Function.identity();

20. COMPOSE LIKE A PRO
Function composition
f : X → Y
g : Y → Z
g ∘ f : X → Z
Function<String,Integer>f=String::length;
Function<Integer,Float>g=Integer::floatValue;
Functionh=g.compose(f);

21. CURRY LIKE A PRO
Function<String,UnaryOperator<String>>curried=
s1->s2->s1.concat("").concat(s2);
//Partialapplication
UnaryOperator<String>hask=curried.apply("Haskell");
out.println(hask.apply("Curry"));
out.println(hask.apply("Wexler"));
*Curryingis afancyname for schönfinkeling

22. CURRY LIKE A SEMI-PRO
Can'tcurryanyfunction like (a, b) → a+ b;
Butwe have tools:
publicinterfaceCurry{
static<T,U,R>Function<U,R>curry(BiFunction<T,U,R>bi,Tt){
returnu->bi.apply(t,u);
}
}
BiFunction<String,Integer,Float>bi=(s,i)->(s.length()+i)/2.0f;
//Can'tdobi.curry("hello")foranybi
Function<Integer,Float>part=Curry.curry(bi,"hello");
//Willwebeablecallpart(10)someday?
out.println(part.apply(10));
out.println(part.apply(22));

23. JAVA.UTIL.FUNCTION.*
Function<T, R>
BiFunction<T, U, R>
Predicate<T>
Supplier<T>
Consumer<T>
BiConsumer<T, U>
UnaryOperator<T> : Function<T, T>

24. STREAMS
filter
map
flatMap
distinct
sorted
limit
These are intermediate operations
Theyare alllazy.

25. STREAMS
forEach *
forEachOrdered
toArray
reduce
collect*
min, max, count, sum
(any|all|none)Match
findAny*
These are terminaloperations
Theyare notlazyatall.
No elementwillbe produced untilyou callone of these.
*Collectors api: toList(), counting(), joining(), etc.

26. PARALLEL STREAMS
From sequentialto parallelin the blink of an eye
lns=names.parallelStream().collect(groupingBy(String::length));
lns.forEach((key,ns)->out.println(key+":t"+
ns.stream().collect(joining(","))));

27. FAILED COMPUTATION?
findAny()returns specialcontainer objectOptional
isPresent, ifPresent(Consumer)
orElse, orElse(Supplier), orElseThrow
Treatlike collection: map, flatMap, filter
Create Optional: empty, of(val), ofNullable(val)
Aconvenientwayto representresultabsence.
(And reduce NPE count.)

28. NO MORE PERMGEN
No more PermGen space errors and PermGen tuning.
Javasays:
VM warning: ignoringoption MaxPermSize=512m;
supportwas removed in 8.0
Jon Masamitsu:
Agoal for removing permgen was so thatusers
do nothave to thinkaboutcorrectly sizing it.
— Butwhere are myclass instances?

29. METASPACE!

30. METASPACE!
java.lang.OutOfMemoryError: Metadataspace

31. METASPACE
Native memoryregion for class data.
Grow automaticallybydefault.
Garbage collected.
-XX:MetaspaceSize -XX:MaxMetaspaceSize
Transition to Java8: e/Perm/Metaspace/g

32. BUT, OLEG, WAIT!
— You said this is Hipster slides, butyou didn'teven mention a
monad!
— Sorryguys. No monads untilwe'llhave Higher Kinded
Polymorphism in Java!

33. Source: ,
THE END
BY OLEG PROPHET / HAKUTAKU.ME
slides javasamples
Thank you!