JavaSlang JavaDayKiev 2016

Transcript

1. Javaslang - Functional Java
   Done Right
   Grzegorz Piwowarek
   gpiwowarek@gmail.com
   1
   

   View Slide

2. Me
   Dev@TouK
   Yoyo Player
   Musician
   2
   

   View Slide

3. pivovarit@
   Twitter
   GitHub
   ...everywhere else
   3
   

   View Slide

4. pivovarit#2152
   4
   

   View Slide

5. Java 8
   5
   

   View Slide

6. "Functional" Java8:
   Lambda Expressions
   Optional, Stream, CompletableFuture
   ...
   6
   

   View Slide

7. View Slide

8. Java 8 issues:
   Only 3 functional control structures
   No memoization
   No lifting
   No pattern matching
   No tuples
   Optional not Serializable/Iterable
   Lack of Stream/Optional in APIs
   Checked exceptions in functions
   "Type pollution"
   list.stream().map(...).collect(toList())
   ...
   8
   

   View Slide

9. List foo(List list);
   9
   

   View Slide

10. List foo(List list) {
    if (this.state.isEmpty() || list.isEmpty()) {
    throw new IllegalStateException("Ouch...");
    }
    list.add(this.state.get(0));
    list.add(CONSTANT);
    this.moreState.addAll(list);
    OtherClass.mutableStaticField = list;
    return list;
    }
    10
    

    View Slide

11. Potential inputs:
    declared params
    instance state
    global state
    Potential outputs:
    declared returned value
    mutable instance state
    mutable global state
    mutable params
    exceptions
    11
    

    View Slide

12. Potential inputs:
    declared params
    Potential outputs:
    declared returned value
    12
    

    View Slide

13. Functional programming is not
    about lambdas.
    13
    

    View Slide

14. "Functional programming is about writing pure functions,
    about removing hidden inputs and outputs as far as we can,
    so that as much of our code as possible
    just describes a relationship between inputs and outputs."
    http://blog.jenkster.com/2015/12/what-is-functional-programming.html
    14
    

    View Slide

15. Immutability
    Referential
    Transparency
    15
    

    View Slide

16. View Slide

17. View Slide

18. Java Collections API:
    add()
    remove()
    clear()
    ...
    18
    

    View Slide

19. Date date = new Date();
    Set dates = new HashSet<>();
    dates.add(date);
    date.setTime(42);
    dates.contains(date); //false
    19
    

    View Slide

20. View Slide

21. λ
    Tuple
    Value
    21
    

    View Slide

22. λ
    Function2 sum = (a, b) -> a + b;
    CheckedFunction2 sum = (a, b) -> a + b;
    composition
    lifting
    currying
    memoization
    22
    

    View Slide

23. Lifting
    Function2 divideBy = (a, b) -> a / b;
    Function2> lift = lift(divideBy);
    23
    

    View Slide

24. Currying
    Function2 sum = (a, b) -> a + b;
    Function1> curried = sum.curried();
    Function1 add2 = curried.apply(2);
    24
    

    View Slide

25. Memoization
    Function2 sum = (a, b) -> a + b;
    Function2 memoizedSum = sum.memoized();
    25
    

    View Slide

26. Function0 mem = Function0.of(Math::random).memoized();
    double randomValue1 = memoizedRand.apply();
    double randomValue2 = memoizedRand.apply();
    then(randomValue1).isEqualTo(randomValue2);
    26
    

    View Slide

27. Tuple
    Tuple2 java8 = Tuple.of("Java", 8);
    Tuple2 that = java8.map(
    s -> s + "slang",
    i -> i / 4);
    String transform = java8.transform((s, i) -> s + i);
    Iterable> objects = java8.toSeq()
    27
    

    View Slide

28. Value
    Option
    Try
    Lazy
    Either
    Future
    Validation
    Collections API
    public interface Value extends Iterable
    28
    

    View Slide

29. Option
    29
    

    View Slide

30. final String result = Option.of(somethingNullable)
    .map(Object::toString)
    .map(String::toLowerCase)
    .getOrElse(() -> "DEFAULT VALUE");
    30
    

    View Slide

31. List> list = ...
    list.stream()
    .filter(Optional::isPresent)
    .map(Optional::get)
    .collect(toList());
    List> list = ...
    list.flatMap(o -> o);
    Java 8
    Javaslang
    31
    

    View Slide

32. Try
    32
    

    View Slide

33. Try.of(() -> new URI("bebebe"))
    .map(URI::getScheme)
    .getOrElse(() -> "UNKNOWN");
    33
    

    View Slide

34. Lazy
    34
    

    View Slide

35. Lazy lazy = Lazy.of(this::veryLongComputation)
    .map(Object::toString)
    .map(String::toUpperCase);
    lazy.get();
    35
    

    View Slide

36. Functional Data
    Structures
    36
    

    View Slide

37. Functional Data Structures:
    Persistent
    Immutable
    with Referential Transparent methods
    37
    

    View Slide

38. Seq
    38
    

    View Slide

39. View Slide

40. public static Stream fibonacci() {
    return Stream.of(1, 1)
    .appendSelf(self -> self.zip(self.tail())
    .map(t -> t._1 + t._2));
    }
    40
    

    View Slide

41. Pattern Matching
    41
    

    View Slide

42. String on = Match(i).of(
    Case(x -> x % 2 == 0, "Even"),
    Case(x -> x % 2 == 1, "Odd"),
    Case($(), "?"));
    Option on = Match(i).option(
    Case(x -> x % 2 == 0, "Even"),
    Case(x -> x % 2 == 1, "Odd"));
    42
    

    View Slide

43. String on = Match(i).of(
    Case($(1), "One"),
    Case($(2), "Two"),
    Case($(), "Something else"));
    43
    

    View Slide

44. Match(localDate).of(
    Case(LocalDate(2016, 2, 13), () -> "2016-02-13"),
    Case(LocalDate(2016, $(), $_), m -> "month " + m + " in 2016"),
    Case(LocalDate($(2016), $(), $_), (y, m) -> "my" + m + y),
    Case($_, () -> "(catch all)")
    );
    44
    

    View Slide

45. String actual = Match(opt).of(
    Case(Some($()), String::valueOf),
    Case(None(), "no value"));
    45
    

    View Slide

46. Match(i).of(
    Case(is(1), "1"),
    Case(isIn(2, 3), "2 or 3"),
    Case(anyOf(is(4), noneOf(is(5), is(6))), "4 or not (5 or 6)"),
    Case(instanceOf(String.class), "String content"),
    Case($(), "?")
    );
    http://koziolekweb.pl/2016/06/18/pattern-matching-w-javie-z-javaslang-ii/
    46
    

    View Slide

47. Match(param).of(
    Case(isIn("-h", "--help"), o -> run(outerWorld::displayHelp)),
    Case(isIn("-v", "--version"), o -> run(outerWorld::displayVersion)),
    Case($(), o -> {}));
    47
    

    View Slide

48. Try.of(this::doSomething)
    .recover(x -> Match(x).of(
    Case(instanceOf(Exception_1.class), ...),
    Case(instanceOf(Exception_2.class), ...),
    Case(instanceOf(Exception_n.class), ...)
    ))
    .getOrElse(other);
    48
    

    View Slide

49. www.javaslang.io
    49
    

    View Slide

50. Thank you!
    gpiwowarek@gmail.com
    pivovarit@twitter (slides are here!)
    pivovarit@github
    50
    

    View Slide