java8-patterns

1. #JCConf Java 8 Patterns

2. #JCConf Agenda • Fluent Decorator • In, Out, In, Out, Shake It All About • The Lonely Override • Monad • Functional Reactive? 2

3. #JCConf Fluent Decorator 3

4. #JCConf Comparator • Building a Comparator before Java 8 • Java 8 Wait! you’re cheating!! It‘s not the reverse order. 4

5. #JCConf • Use Comparator.reverseOrder • Use Comparator.comparing • High order function Anonymous inner classes were designed to make it easier for Java programmers to pass around code as data. 5

6. #JCConf • Order nulls before non-null elements. • Decorator Pattern 6

7. #JCConf • Can you figure out this? Refactor it to nullsFirst(byStringLength())？ 7

8. #JCConf • This would be better! • last name, and then first name, zip code … 8

9. #JCConf • Refactor the Decorator pattern itself 9

10. #JCConf In, Out, In, Out, Shake It All About《Java 8 Lambdas》 10

11. #JCConf Logger • Invoke isLoggable only to check whether calling a method on the Logger • it uses information from the rental, but does not use information from the customer • the method is on the wrong object 11

12. #JCConf Logger • Invoke isLoggable only to check whether calling a method on the Logger • it uses information from Logger, but only to push a value into it • the block is on the wrong object 12

13. #JCConf Map • it uses information from the Map, but only to push a value into it. • the block is on the wrong object. • computeIfPresent、compute、merge … 13

14. #JCConf The Lonely Override《Java 8 Lambdas》 14

15. #JCConf ThreadLocal • Subclass solely to override a single method • What you really want is providing a block of code to the method! 15

16. #JCConf • This wasn't an antipattern before Java 8—it was the idiomatic way of writing this code • Source code of withInitial 16

17. #JCConf Monad Patterns 17

18. #JCConf Optional • Null sucks, right? • Optional is trendy now! Optional<Order> WET 18

19. #JCConf • Behavioral WET（Write Everything Twice） – You create Optional<T> – invoke isPresent of Optional<T> – if true, get and map T to Optional – if false, return Optional.empty() • You uses information from Optional<T>, but only to get a Optional from it • In, Out, In, Out, Shake It All About 19

20. #JCConf • Let's flatMap repeatedly. • Using method reference is much clearer. • Monad? Why is it important? – Enable me to talk about monad right now!! 20

21. #JCConf • Seriously, a monad is a pattern – You create M<T> – do actions on M<T> – get and map T value(s) to M – do actions on M or else • Optional Monad – You create Optional<T> – invoke isPresent of Optional<T> – if true, get and map T to Optional – if false, return Optional.empty() 21

22. #JCConf • Seriously, a monad is a pattern – You create M<T> – do actions on M<T> – get and map T value(s) to M – do actions on M or else • Optional Monad – You create Optional<T> – invoke isPresent of Optional<T> – if true, get and map T to Optional – if false, return Optional.empty() Hide the boilerplate of computational context Hide the boilerplate of "if non-null“ logic 22

23. #JCConf 23

24. #JCConf Stream • for loop hell ... XD • Call back hell ... XD 24

25. #JCConf • Stream Monad – You create Stream<T> – forEach T element – map T to Stream • A simpler example Hide the boilerplate of nested loops 25

26. #JCConf • The flatMap operation 4 1 1 2 3 4 5 6 flatMap(List<Integer> to Stream<Integer>) 26

27. #JCConf CompletableFuture • A monad is a pattern – You create M<T> – do actions on M<T> – get and map T value(s) to M – do actions on M or else Hide the boilerplate of computational context 27

28. #JCConf • Lambda rocks! • Lambda sucks!! – You create Future<T> – wait until T is ready (in another thread) – use T and the supplied code to create Future Hide the boilerplate of thread logic. You‘ve done that. Future<String> 28

29. #JCConf • CompletableFuture Monad flatMap CompletableFuture<String> CompletableFuture<String> 29

30. #JCConf • Composable Future solo birthdays 30

31. #JCConf Functional Reactive? 31

32. #JCConf Functional Reactive Programming • Reactive • Data flow • Propagation of change • Observer • Functional • Asynchronous • … WTF? 32

33. #JCConf Reactive Programming • A programming paradigm oriented around data flows and the propagation of change 33

34. #JCConf • If Java supports reactive programming directly, it should ... • Of course, it's impossible in the language level for Java. • Model-View-Controller architecture can allow changes in the underlying model to automatically be reflected in the view (10, 15, 25) (20, 25, 35) 34

35. #JCConf Observer • In MVC, Model-View could be implemented by the Observer pattern. • Maybe, we can ... (10, 15, 25) (20, 25, 35) 35

36. #JCConf songs • When things become complex ... names albums 1900s soloartists songs songs songs songs lengths nationalities birthdays 36

37. #JCConf • RxJava Observable • Look up artist information • filter、flatMap? map? Stream? Observable<Artist> 37

38. #JCConf Functional Reactive Programming • A programming paradigm for reactive programming using the building blocks of functional programming • filter、map、reduce、flatMap are patterns from functional programming 38

39. #JCConf • Stream builds up computational workflows over in-memory collections • Observable composes and sequences asynchronous and event-based systems. Instead of pulling data out, it gets pushed in • CompletableFuture is to a single value • Observable is a sequence of values 39

40. #JCConf Asynchronous • "that executes in whole seconds is probably doing something wrong…" - Brendan Eich • it's 100 milliseconds from research conducted by Robert Miller 40

41. #JCConf • Make a mountain out of a molehill … XD 41

42. #JCConf Summary • Design patterns evolve more and more exquisitely since Java 8. • Lambda furthers advanced refactoring. • As the language evolves, so do the idioms that you use when programming. • A monad is a pattern. • Functional reactive programming is a mixture of multi patterns and paradigms. 42

43. #JCConf References • http://books.gotop.com.tw/v_ACL042200 • http://www.slideshare.net/JustinSDK/jdk8- functional-api • http://www.slideshare.net/mariofusco/monadic-java • http://shop.oreilly.com/product/0636920030713.do • http://en.wikipedia.org/wiki/Reactive_programming • https://github.com/ReactiveX/RxJava • https://speakerdeck.com/benjchristensen/functional -reactive-programming-with-rxjava-javaone-2013 • http://shop.oreilly.com/product/9780596802806.do 43

44. #JCConf Thanks!! 44