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Why Scala is the better Java

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Veröffentlicht am

Talk am Technologieplauscherl 33, 14.01.2016

Veröffentlicht in: Software
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Why Scala is the better Java

  1. 1. Why Scala is the better Java Thomas Kaiser Technologieplauscherl 14.01.2016
  2. 2. Agenda • Why this talk • Cool language features • Pitfalls and how to avoid them • Resources
  3. 3. Quick survey • Who... • ... Writes Java code for production? • ... Has ever written any Scala code? • ... Has ever written Scala for production? • Me • Java background (Spring, Hibernate, Grails, GWT, Android) • Scala webapp w/ Postgres, Mongo, Play, Angular, REST
  4. 4. What is Scala • JVM based functional/OO language • Powerful type system • Traits/mixins • Higher-order functions • Pattern matching • Concurrency abstractions
  5. 5. Why this talk • People are interested in Scala, but also afraid? • Scala is extremely powerful and flexible • Syntax • Huge library • Lots of ways to do the same thing • Very intimidating type system • BUT! You don‘t have to use any of the advanced features and still benefit massively
  6. 6. Why Scala • Extremely expressive (LOC--) • Static typing • Very clean style comes built-in • Awesome (awesome) library (collections etc) • Writing Scala code is actually fun!
  7. 7. Language features (why I love Scala) • Tuples • String concatenation • Local functions • Import aliases • Super-easy collection/map creation • Powerful collections library • Traits • Case classes • Pattern matching • Function values/function literals • Multiple parameter lists • Option[T] • For-Comprehensions • Everything is a value • Syntax flexibility • Type inference • JSON/XML handling • Scalatest/specs2 • Implicit conversions • Annymous/structural types, type aliases • Algebraic data types
  8. 8. S vs. J: Boilerplate public class User { private String name; private List<Order> orders; public User() { orders = new ArrayList<Order>(); } public String getName() { return name; } public void setName(String name) { this.name = name; } public List<Order> getOrders() { return orders; } public void setOrders(List<Order> orders) { this.orders = orders; } } public class Order { private int id; private List<Product> products; public Order() { products = new ArrayList<Product>(); } public int getId() { return id; } public void setId(int id) { this.id = id; } public List<Product> getProducts() { return products; } public void setProducts(List<Product> products) { this.products = products; } } public class Product { private int id; private String category; public int getId() { return id; } public void setId(int id) { this.id = id; } public String getCategory() { return category; } public void setCategory(String category) { this.category = category; } }
  9. 9. S vs. J: Boilerplate case class User(name: String, orders: List[Order]) case class Order(id: Int, products: List[Product]) case class Product(id: Int, category: String)
  10. 10. S vs. J: Standard use case – extract data • Get products of a User public class User { ... public List<Product> getProducts() { List<Product> products = new ArrayList<Product>(); for (Order order : orders) { products.addAll(order.getProducts()); } return products; } }
  11. 11. S vs. J: Standard use case – extract data • Get ordered products of a User def products = orders.flatMap(o => o.products)
  12. 12. S vs. J: Remove x highest values public static List<Integer> removeHighestValuesJ6( List<Integer> values, int amount) { List<Integer> localValues = new ArrayList<>(values); Collections.sort(localValues); int toIndex = localValues.size() - amount; if (toIndex < 0) { toIndex = 0; } return localValues.subList(0, toIndex); } public static List<Integer> removeHighestValuesJ8( List<Integer> values, int amount) { Collections.sort(values); // in-place! boo! Collections.reverse(values); // in-place! List<Integer> result = values.stream() .skip(amount) .collect(Collectors.toList()); return result; }
  13. 13. S vs. J: Remove x highest values def removeHighestValues(list: List[Int], amount: Int) = { list.sorted.reverse.drop(amount) }
  14. 14. For comprehensions each++ for (i <- 1 to 7) print(i) // 1234567 for (i <- 1 to 7 if i % 2 == 0) print(i) // 246 case class Person(age: Int) val persons = for (i <- 20 to 35 by 5) yield Person(i) // Person(20), Person(25), Person(30), Person(35)
  15. 15. Pattern matching case class Person(name: String, age: Int) val p1 = Person("thomas", 29) val p2 = Person("dominik", 32) p2 match { case Person("thomas", 29) => "exactly that person" case Person(_, age) if age > 30 => "anyone over 30" case p : Person => s"just binding to a variable (${p.name})" }
  16. 16. Pattern matching val list = List(1, 2, 3) list match { case 1 :: 2 :: rest => "list starts with 1,2 and has " + rest.length + " more" }
  17. 17. Everything is a value val bool = true val yepNope = if (bool) "yep" else "nope" case class AuthUser(email: String, roles: Set[String]) val currentUser = AuthUser(”user", Set("ADMIN")) val isAuthorized = currentUser match { case AuthUser(_, roles) if roles.contains("ADMIN") => true case _ => false }
  18. 18. Everything is a value def russianRoulette() = if (Random.nextInt(6) == 0) throw new RuntimeException(“bang“) else "phew“ val dangerousResult: String = try { russianRoulette() } catch { case RuntimeException => "dead :(“ }
  19. 19. Implicit conversions val hello: String = "hello" hello.emphasize // Error:(32, 8) value emphasize is not a member of String „Pimp my library pattern“ implicit class PimpedString(base: String) { def emphasize = base + "!!!11" } import PimpedString val pimpedString = hello.emphasize // hello!!!11
  20. 20. Implicit conversions for (i <- 1 to 7) <=> 1.to(7) <=> val r: Range = new RichInt(1).to(7)
  21. 21. DSLs class HelloWorldSpec extends Specification { "Hello world" should { val hw = "Hello world" “be 11 chars long" in { hw should have size 11 } "start with hello" in { hw should startWith "hello“ } } }
  22. 22. DSLs "show off some mocking DSL" in { val m = mock[List[String]] m.get(0) returns “0" // .. code under test ... there was one(m).get(0) }
  23. 23. DSLs val messageFlow = filter { payload: String => payload == "World" } --> transform { payload: String => "Hello " + payload } --> handle { payload: String => println(payload) } messageFlow.send("World") // "Hello World"
  24. 24. Implicit conversions for (i <- 1 to 7) <=> 1.to(7) <=> val r: Range = new RichInt(1).to(7) Map(1 -> "one") <=> 1.->("one") <=> val entry : (Int, String) = new ArrowAssoc[Int](1).->("one”) val x = Future { ... } Await.result(x, 5 seconds) <=> new DurationInt(5)
  25. 25. Pitfalls • Implicits can be confusing • Many different codestyles in the wild • Hard to understand libraries • Yet another build tool (SBT)
  26. 26. Take away • Just do it! • You can always go back or mix Java and Scala code • ... But you won‘t • Be wary of advanced language features • Don‘t be scared, you don‘t have to use anything • Use it as a very expressive, fun, supercharged Java • ... And you won‘t look back • „Scalable language“
  27. 27. Resources • http://scala-lang.org/ • http://docs.scala-lang.org/cheatsheets/ • List of links (!!) • Learning functional programming without growing a neckbeard • https://github.com/pocorall/scaloid (Scala4Android, super cool)

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