The document presents the features and enhancements introduced in Java 8 from a functional programming perspective, highlighting default methods, lambda expressions, and the new date/time API. It discusses the removal of PermGen space errors, the introduction of streams for handling collections, and the use of functional interfaces to support functional programming paradigms. Additionally, the slides emphasize the importance of type inference and method references, showcasing various examples to illustrate the capabilities of Java 8.

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!