Clean Lambdas & Streams in Java8

1. Enterprise Java Training Victor Rentea 10 March 2017 Clean Lambdas & Streams in Java 8 A Hands-on Experience Workshop: Searching Streams (30 min) Workshop: Transforming Streams (40 min) Workshop: Cleaning Lambdas (20 min) Conclusions: Best Practices (20 min) Agenda www.victorrentea.ro victor.rentea@gmail.com @victorrentea © Copyright Victor Rentea 2017

2. VictorRentea.ro Clean Code Evangelist International Speaker  Spring and  Clean Code, Design Patterns ( )  TDD, Coding Dojos  Java Performance  many more: Victor Rentea, PhD(CS) Consultant, Technical Lead Lead Architect for major client at IBM Romania Night Job : Freelance Trainer & Coach victorrentea@gmail.com www.victorrentea.ro@victorrentea 2

3. VictorRentea.ro They are cool Expressive code - .filter(Order::isActive) Concise code (½ lines?) Cryptic? Hard to read? - What guidelines to follow ? Why Lambdas ? 3

4. VictorRentea.ro Which λ to use in enterprise Java apps ? - Readable, maintainable - vs Java7 - Questionnaire-based - Java8 features in examples from production - For Java developers of any exp level (min 3 months of Java8 hands-on) - Wanna submit you answer? Thank you !! : http://bit.ly/2dFf2fi My own little Clean Lambdas Study 4

5. VictorRentea.ro Workshop: Searching Streams (30 min) Workshop: Transforming Streams (40 min) Workshop: Cleaning Lambdas (20 min) Conclusions: Best Practices (20 min) Agenda 5

6. VictorRentea.ro // Cool Class Diagram [Order|id:Long;creationDate;paymentMeth od;status:Status;totalPrice:BigDecimal]- orderLines*>[OrderLine|count:int;isSpecial Offer] [OrderLine]-product>[Product|name] [Audit|action;date;user;modifiedField] Before we start: configure your IDE to suggest static imports of: java.util.stream.Collectors.* and java.util.Comparator.comparing In Eclipse: Preferences > type “favo” > Favorites > New Type & New Member Our Domain Model  6

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32. VictorRentea.ro static method constructor Method References 32 Integer::parseInt Order::getCreationDate OrderMapper::toDto String::length myOrder::getCreationDate orderMapper::toDto firstName::length Date::new ... of a class … of an instance instance method instance is known 𝒇(𝑶𝒓𝒅𝒆𝒓): 𝑫𝒂𝒕𝒆 𝒇(𝑺𝒕𝒓𝒊𝒏𝒈): 𝒊𝒏𝒕 𝒇(𝑶𝒓𝒅𝒆𝒓𝑴𝒂𝒑𝒑𝒆𝒓, 𝑶𝒓𝒅𝒆𝒓): 𝑶𝒓𝒅𝒆𝒓𝑫𝒕𝒐 𝒇(): 𝑫𝒂𝒕𝒆 𝒇(): 𝒊𝒏𝒕 𝒇 𝑶𝒓𝒅𝒆𝒓 : 𝑶𝒓𝒅𝒆𝒓𝑫𝒕𝒐 𝒇(𝑺𝒕𝒓𝒊𝒏𝒈): 𝒊𝒏𝒕 𝒇(): 𝑫𝒂𝒕𝒆 𝒇(𝑳𝒐𝒏𝒈): 𝑫𝒂𝒕𝒆

33. VictorRentea.ro = (String s) -> {return s.length();}; Function<String, Integer> stringLen = (String s) -> s.length(); // implicit return = s -> s.length(); = String :: length; Comparator<User> fNameComparator = (u1,u2)-> u1.getFName().compareTo(u2.getFName()); = Comparator.comparing(User :: getFName); Predicate<Apple> appleIsHeavy = a -> a.getWeight() > 150; = Apple :: isHeavy; Consumer<String> stringPrinter = s -> System.out.println(s); // returns void = System.out::println; Supplier<Wine> firstMiracle = () -> new Wine(); = Wine :: new; 𝒇 𝑺𝒕𝒓𝒊𝒏𝒈 : 𝑰𝒏𝒕𝒆𝒈𝒆𝒓 𝒇 𝑼𝒔𝒆𝒓, 𝑼𝒔𝒆𝒓 : 𝒊𝒏𝒕 𝒇 𝑨𝒑𝒑𝒍𝒆 : 𝒃𝒐𝒐𝒍𝒆𝒂𝒏 𝒇 𝑺𝒕𝒓𝒊𝒏𝒈 𝒇(): 𝑾𝒊𝒏𝒆 ʎ syntax 33

35. VictorRentea.ro flatMap(i -> i.getChildren().stream()) 35

36. VictorRentea.ro 2 4 1 3 0 2+ .reduce(0, +) 6+ 7+ 10+ 36

50. VictorRentea.ro50 orders.stream() .filter(Order::isActive) .map(Order::getCreationDate) .collect(toList())

51. VictorRentea.ro51 orders.stream() .filter(Order::isActive) .map(Order::getCreationDate) .collect(toList()) Give me! Here you go! Give me! Give me! Argh! Another one! Here you go!

52. VictorRentea.ro52 .filter(Order::isActive) orders.stream() .map(Order::getCreationDate) Give me! Nope! I’m done. .collect(toList()) .limit(3) ARENEVERSEEN

53. VictorRentea.ro53 .filter(Order::isActive) .map(Order::getCreationDate) .findFirst() orders.stream() ARENEVERSEEN I’m done.

54. VictorRentea.ro54 Short Circuiting

56. VictorRentea.ro56 The most important principle in Programming?

57. VictorRentea.ro57 ingle esponsibility rincipleS R P

58. VictorRentea.ro58 Keep It Short & SimpleK I S S

59. VictorRentea.ro59 KISS (or nullable): SRP Work with predicates (coming up next) Simple code Look for the simplest form

60. VictorRentea.ro60 Pair Programming

62. VictorRentea.ro public static Predicate<Order> deliveryDueBefore(Date date) { return order -> order.getDeliveryDueDate().before(date); } Clean Lambdas Encapsulate Predicates Predicate<Order> needsTracking = order -> order.hasPoliticalCustomer(); Set<Customer> customersToNotify = orders.stream() .filter(order -> order.getDeliveryDueDate().before(warningDate) && order.getOrderLines().stream() .anyMatch(line -> line.getStatus() != Status.IN_STOCK)) .map(Order::getCustomer) .collect(toSet()); .filter(order -> order.getDeliveryDueDate().before(warningDate)) .filter(order -> order.getOrderLines().stream() .anyMatch(line -> line.getStatus() != Status.IN_STOCK))(OrderLine::isNotInStock)) .filter(this::hasOrdersNotInStock) <entity> OrderLine <service> NotificationService (this) OrderPredicates.deliveryDueBefore(warningDate))deliveryDueBefore(warningDate)).or(this::needsTracking)) <utility> OrderPredicates  In entities  In the class needing it  As functions returning Predicates  Auxiliary Predicate variables 62

64. VictorRentea.ro64 Find the shortest form (peer review) Don’t abuse them Clean Code Using Java8 New Features (lambdas, Stream, Optional)

65. VictorRentea.ro Resources Java 8 in Action by Raoul-Gabriel Urma, Mario Fusco, Alan Mycroft, 2015 https://blog.jetbrains.com/idea/2016/07/java-8-top-tips/ https://github.com/jOOQ/jOOL Clean Code by Robert C. Martin https://zeroturnaround.com/rebellabs/java-8-best-practices-cheat-sheet/ https://www.journeytomastery.net/2015/03/22/clean-code-and-java-8/ Curious about Java9: https://bentolor.github.io/java9-in-action/ 65

66. Enterprise Java Training www.victorrentea.ro victor.rentea@gmail.com @victorrentea  Workshop: Searching Streams (30 min)  Workshop: Transforming Streams (40 min)  Workshop: Cleaning Lambdas (20 min)  Conclusions: Best Practices (20 min) © Copyright Victor Rentea 2017 Victor Rentea 10 March 2017 Clean Lambdas & Streams in Java 8 A Hands-on Experience