This presentation focuses on proper use of new Java 8 features.

1. JAVA 8LAMBDAS, MONADS && JAVA COLLECTIONS
Grzegorz Piwowarek

2. GRZEGORZ PIWOWAREK
@PIVOVARIT

3. GRZEGORZ PIWOWAREK
@PIVOVARIT
visionsoftondal.com

4. Plan:
-lambda expressions
-java.util.function
-monads
-Optional
-Stream

5. lambda expressions
(...) -> statement
- Anonymous function

6. lambda expressions
x -> x + 1

7. lambda expressions
x -> x + 1
- No type information

8. lambda expressions
x -> x + 1
() -> 42
() -> {return 42;}
(x, y) -> {}
() -> {}

9. method references

10. java.util.function

11. java.util.function

12. java.util.function

13. Function<T, R>, BiFunction<T,U,R>
Consumer<T> extends Function<T,Void>
Supplier<T> extends Function<Void, T>
Predicate<T> extends Function<T, Boolean>
UnaryOperator<T> extends Function<T, T>
BinaryOperator<T> extends BiFunction<T,T,T>

14. Function<T, R>, BiFunction<T,U,R>
Consumer<T> extends Function<T,Void>
Supplier<T> extends Function<Void, T>
Predicate<T> extends Function<T, Boolean>
UnaryOperator<T> extends Function<T, T>
BinaryOperator<T> extends BiFunction<T,T,T>

15. Function<T, R>, BiFunction<T,U,R>
Consumer<T> extends Function<T,Void>
Supplier<T> extends Function<Void, T>
Predicate<T> extends Function<T, Boolean>
UnaryOperator<T> extends Function<T, T>
BinaryOperator<T> extends BiFunction<T,T,T>

16. Function<T, R>, BiFunction<T,U,R>
Consumer<T> extends Function<T,Void>
Supplier<T> extends Function<Void, T>
Predicate<T> extends Function<T, Boolean>
UnaryOperator<T> extends Function<T, T>
BinaryOperator<T> extends BiFunction<T,T,T>

17. Function<T, R>, BiFunction<T,U,R>
Consumer<T> extends Function<T,Void>
Supplier<T> extends Function<Void, T>
Predicate<T> extends Function<T, Boolean>
UnaryOperator<T> extends Function<T, T>
BinaryOperator<T> extends BiFunction<T,T,T>

18. MONAD

20. GOOGLE IMAGES...

21. ...

22. MONAD
Design pattern

23. MONAD
Design pattern
http://got-steam.com/

24. Why bother? :
Boilerplate -1
Readability +1
Complexity -1
Responsibility -1

25. type: M<T>
"unit": T -> M<T>
"bind": M<T> bind(T -> M<U>) = M<U>
MONAD
"bind": M<T> bind(T -> U)= M<U>

26. type: M<T>
"unit": T -> M<T>
"bind": M<T> bind(T -> M<U>) = M<U>
MONAD
"bind": M<T> bind(T -> U)= M<U>

27. "bind": M<T> bind(T -> U)= M<U>
What if U: M<?> ?

28. "bind": M<T> bind(T -> U)= M<U>
What if U: M<?> ?
http://www.ivanaborovnjak.com/project/box-in-a-box/

29. "bind": M<T> bind(T -> U)= M<U>
What if U: M<?> ?
http://www.ivanaborovnjak.com/project/box-in-a-box/

30. Monads in Java 8
Optional
Stream
CompletableFuture

31. Monads in Java 8
Optional
Stream
CompletableFuture

32. Optional
Encapsulation of operations
on optional values

33. Optional
type: M<T>
"unit": T -> M<T>
"bind": M<T> bind(T -> M<U>) = M<U>

34. Optional
type: Optional<T>
"unit": T -> M<T>
"bind": M<T> bind(T -> M<U>) = M<U>

35. Optional
type: Optional<T>
"unit": Optional.ofNullable(), Optional.of()
"bind": M<T> bind(T -> M<U>) = M<U>

36. Optional
type: Optional<T>
"unit": Optional.ofNullable(), Optional.of()
"bind": Optional.flatMap()

37. Filtering an Optional
.filter(Predicate<T>)

38. Unwrapping an Optional
.get()
.orElse(T default)
.orElseGet(Supplier<T>)
.orElseThrow(Supplier<Ex>)
.ifPresent(Consumer<T>)

39. Java 7 style

40. Java 8 style

41. Java 8 style - flatMap

42. Java 7,5 style ;)

43. Java 7,5 style ;)

44. Stream
Encapsulation of operations
on multiple items

45. Stream
type: Stream<T>
"unit": Stream.of(), Arrays.stream(), Collection.stream()
"bind": Stream.flatMap()

46. Stream
lazy-initialized
nonreusable

47. Java7

48. Java8

49. Stream && Optional

50. intermediate operations
.map()
.flatMap()
.filter()
.peek()

51. intermediate operations
.map()
.flatMap()
.filter()
.peek()
Stream not consumed:
does not print anything

52. Consuming Stream
.forEach(Consumer<T>)
.collect()
.reduce(BinaryOperator<T>)
.allMatch(), anyMatch(), noneMatch()
.findFirst(), findAny()
.count()
.toArray()

53. Stream.reduce()

54. Collectors
.toList(), toMap(), toSet(), toCollection()
.minBy(), maxBy()
.joining()
.partitioningBy()
...and many others

55. Collectors.toList()

56. Collectors.toMap()

57. Collectors.joining()

58. Stream in APIs
BufferedReader.lines()
Files.newDirectoryStream()
Random.ints()
...

59. you want more?

60. https://github.com/
jasongoodwin/better-java-monads

61. Thank You!

62. REFERENCES:
-MONADIC JAVA BY MARIO FUSCO
-WHAT'S WRONG WITH JAVA 8 BY PIERRE-YVES SAUMONT
-WWW.ORACLE.COM