Introduction to Scala

SCALA
Java Klassentreffen 2013
Manuel Bernhardt

@elmanu Java Klassentreffen 2013 - javatraining.at
AGENDA
• History
• Why Scala?
• Scala in the wild
• The Code / Scala in practice
• Tools & more

YOUR SPEAKER
• Independent software
consultant
• Web, web, web
• Java & Scala & Javascript
• Open-Source
• Delving

HISTORY
• Martin Odersky, EPFL
• Espresso, Pizza, GJ, Javac
• Funnel, Scala
• First Scala release in
2003

AGENDA
• History
• Why Scala?
• The Code / Scala in practice

SCALA DESIGN GOALS

SCALA DESIGN GOALS
• Full interoperability with Java

SCALA DESIGN GOALS
• Cut down boilerplate

SCALA DESIGN GOALS
• Pure object orientation & functional programming

SCALA DESIGN GOALS
• Move away from null

SCALA DESIGN GOALS
• Move away from null
• Multi-core programming

WHAT PEOPLE SAY
If I were to pick a language today
other than Java, it would be Scala.
James Gosling
Father of Java

WHAT PEOPLE SAY
I can honestly say if someone had
shown me the Programming Scala
book by Martin Odersky, Lex Spoon
& Bill Venners back in 2003 I’d
probably have never created Groovy.
James Strachan
Creator of Groovy

ThoughtWorksTechRadar May 2013
http://www.thoughtworks.com/radar

SCALA INTHE WILD

SCALA INTHE WILD
etc.

SCALA INVIENNA
• openForce - http://openforce.com
• x-tradesoft - http://xtradesoft.com
• Delving - http://www.delving.eu
• dimocom - http://www.dimocom.com
• emarsys - http://www.emarsys.com
• Miavia - https://miavia.in

SCALA INVIENNA
• ScalaVienna User Group
• http://scala-vienna.org/
Next meeting: 26th
September 6 PM - Sektor 5

AGENDA
• History
• Why Scala?
• The Code / Scala in
practice
• Tools & more

AVOIDINGTHE BILLION-
DOLLAR MISTAKE
But I couldn't resist the
temptation to put in a null
reference, simply because it
was so easy to implement
Tony Hoare
Creator of ALGOL

AVOIDINGTHE BILLION-
DOLLAR MISTAKE
val maybeUser: Option[User] = User.findOneByName("bob")
// returns Some[User]
maybeUser == None // false
maybeUser.foreach { user =>
println(user.fullName)
// prints "Bob Marley" if there is a user!
}
val name = maybeUser.map(_.name).getOrElse("Unknown user")

CONCISENESS
public class User {
! private String name;
! private String surname;
! private String email;
! public User(String name, String surname, String email) {
! ! this.name = name;
! ! this.surname = surname;
! ! this.email = email;
! }
! public void setName(String name) {
! }
! public void setSurname(String surname) {
! }
! public void setEmail(String email) {
! ! this.email = email
! }
! public String getName() {
! ! return this.name;
! }
! public String getSurname() {
! ! return this.surname;
! }
! public String getEmail() {
! }
}

CONCISENESS
class User(
var name: String,
var surname: String,
var email: String)
val bob = new User("Bob", "Marley", "bob@marley.org")
// bob: User = User@5c3f1224
bob.name // res0: String = Bob
bob.name = "Bobby" // bob.name: String = Bobby

CONCISENESS
public class ImmutableUser {
! private final String name;
! private final String surname;
! private final String email;
! public ImmutableUser(String name, String surname, String email) {
! ! this.email = email;
! }
! public String getName() {
! ! return this.name;
! }
! public String getSurname() {
! }
! public String getEmail() {
! }
! @Override public int hashCode() {
! ! // yada yada yada
! }
! @Override public boolean equals(Object that) {
! ! // yada yada yada
! }
}

CONCISENESS
case class ImmutableUser(
name: String,
surname: String,
email: String)
val bob = ImmutableUser("Bob", "Marley", "bob@marley.org")
// hashcode and equals for free!
val namedBob = ImmutableUser(name = "Bob", surname = "Marley",
email = "email")
val bobby = bob.copy(name = "Bobby")
// returns a User with name Bobby
bob.toString // res0: String = ImmutableUser(Bob,Marley,email)

USEFULTYPE INFERENCE
val foo = "Bar" // foo: String = Bar
val answer = 42 // answer: Int = 42
val price = 9.99 // price: Double = 9.99
val nums = List(1, 2, 3) // nums: List[Int] = List(1, 2, 3)
val map = Map("abc" -> List(1, 2, 3))
// map: scala.collection.immutable.Map[String,List[Int]] =
Map(abc -> List(1, 2, 3))

EXPLICITTYPING
val foo: String = "Bar" // foo: String = Bar
val answer: Int = 42 // answer: Int = 42
val price: Double = 9.99 // price: Double = 9.99
val nums: List[Int] = List(1, 2, 3) // nums: List[Int] =
List(1, 2, 3)
val map: Map[String, List[Int]] = Map("abc" -> List(1, 2, 3))
// map: scala.collection.immutable.Map[String,List[Int]] =
Map(abc -> List(1, 2, 3))

COLLECTION LIBRARY &
FUNCTIONAL STYLE
users.sort(new Comparator {
public int compare(Object user1, Object user2) {
! int userAge1 = ((User) user1).getAge();
! int userAge2 = ((User) user2).getAge();
! if (userAge1 > userAge2) {
! ! return 1;
! } else if userAge1 < userAge2) {
! ! ! return -1;
! ! } else {
! ! ! return 0;
! ! }
! }
});

FUNCTIONAL STYLE
def sortByAge(user1: User, user2: User) = user1.age > user2.age
users.sortWith(sortByAge)

FUNCTIONAL STYLE
users.sortWith((user1, user2) => user1.age > user2.age)

FUNCTIONAL STYLE
users.sortWith(_.age > _.age)

FUNCTIONAL STYLE
List<User> minors = new ArrayList<User>();
List<User> majors = new ArrayList<User>();
for (User u : users) {
! if (u.getAge() < 18) {
! ! minors.add(u);
! } else {
! ! majors.add(u);
! }
}

FUNCTIONAL STYLE
val (minors, majors) = users.partition(_.age < 18)

FUNCTIONAL STYLE
val minors = users.filter(_.age < 18)

• Minimal language, powerful library
• Language features for extensibility
EXTENSIBLE LANGUAGE

DOMAIN SPECIFIC
LANGUAGES
import collection.mutable.Stack
import org.scalatest._
class ExampleSpec extends FlatSpec with Matchers {
"A Stack" should "pop values in last-in-first-out order" in {
val stack = new Stack[Int]
stack.push(1)
stack.push(2)
stack.pop() should be (2)
stack.pop() should be (1)
}
it should "throw NoSuchElementException if an empty stack is popped" in {
val emptyStack = new Stack[Int]
a [NoSuchElementException] should be thrownBy {
emptyStack.pop()
}
}
}

MACROS
PLAY JSON DE/SERIALIZATION

MACROS
case class Creature(name: String, isDead: Boolean, weight: Float)
implicit val creatureReads: Reads[Creature] = (
(__ "name").read[String] and
(__ "isDead").read[Boolean] and
(__ "weight").read[Float]
)(Creature)
implicit val creatureWrites: Writes[Creature] = (
(__ "name").write[String] and
(__ "isDead").write[Boolean] and
(__ "weight").write[Float]
)(unlift(Creature.unapply))

MACROS
import play.api.json._
implicit val creatureFormat = Json.format[Creature] // format is a macro

IDE
• IntelliJ IDEA
• Eclipse
• SublimeText

SIMPLE BUILDTOOL
name := "My Project"
version := "1.0"
organization := "org.myproject"
libraryDependencies += "org.scala-tools.testing" %% "scalacheck" %
"1.8" % "test"
libraryDependencies ++= Seq(
"net.databinder" %% "dispatch-meetup" % "0.7.8",
"net.databinder" %% "dispatch-twitter" % "0.7.8"
)
javaOptions += "-Xmx256m"
logLevel in compile := Level.Warn

FRAMEWORKS:AKKA
• Actor concurrency model based on Erlang
• “Human” design: actors talk to eachother and form hierarchies
• Much, much, much simpler to work and reason with than
threads

FRAMEWORKS:AKKA
Source: http://prabhubuzz.wordpress.com/2012/09/28/akka-really-mountains-of-concurrency/

FRAMEWORKS:AKKA
class Master extends Actor {
! val workers = context.actorOf(Props[Worker].withRouter(
! RoundRobinRouter(nrOfInstances = 5))
! )
! def receive = {
! ! case Start =>
! ! ! getDocumentsFromDb.foreach { document =>
! ! ! ! workers ! Process(document)
! ! ! }
! ! case Result(processed) => writeResult(processed)
! ! case Stop => children.foreach(stop)
! }
}

FRAMEWORKS:AKKA
class Worker extends Actor {
! def receive = {
! ! case Process(doc: Document) =>
! ! ! val processed = doSomeHardWork(doc)
! ! ! sender ! Result(processed)
! }
}

FRAMEWORKS: PLAY
• MVC framework à la Rails
• Real-time web, streams (WebSocket, ...)
• Everything is compiled
• I mean everything: CSS, JavaScripts,Templates, URLs, JSON, ...

FRAMEWORKS: PLAY
GET /users controllers.Users.list
POST /users controllers.Users.create
PUT /users/:id/update controllers.Users.update(id: Long)
DELETE /users/:id controllers.Users.delete(id: Long)

FRAMEWORKS: PLAY
class Users extends Controller {
def list = Action { request =>
val users = User.findAll
Ok(Json.toJson(users))
}
}

FRAMEWORKS: PLAY
class Users extends Controller {
def list = Action { request =>
val users = User.findAll
Ok(Json.toJson(users))
}
}
200 OK
Content-Type: application/json

THANKYOU!
• Questions, comments ?
• http://logician.eu
• manuel@bernhardt.io
• @elmanu

Introduction to Scala

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