Scala - Java2Days Sofia

SCALA
Java2Days 2013
Manuel Bernhardt

Dienstag, 03. Dezember 13

AGENDA
• History
• Why

Scala?

• Scala

in the wild

• The

Code / Scala in
practice

• Tools
@elmanu

& more

YOUR SPEAKER
• Independent

software
consultant based in Vienna

• Web, web, web
• Scala

& Java & Javascript

• Open-Source

@elmanu

HISTORY
• Martin

Odersky, EPFL

• Espresso, Pizza, GJ,

javac

• Funnel, Scala
• First

Scala release in
2003

@elmanu

AGENDA
• History
• Why
• Scala
• The

Scala?

in the wild

Code / Scala in
practice

@elmanu

SCALA DESIGN GOALS

@elmanu

SCALA DESIGN GOALS
• Full

interoperability with Java

@elmanu

SCALA DESIGN GOALS
• Full


• Cut

down boilerplate

@elmanu

SCALA DESIGN GOALS
• Full


• Cut

down boilerplate

• Pure

@elmanu

object orientation & functional programming

SCALA DESIGN GOALS
• Full


• Cut

down boilerplate

• Pure


• Move

@elmanu

away from null

SCALA DESIGN GOALS
• Full


• Cut

down boilerplate

• Pure


• Move

away from null

• Multi-core
@elmanu

programming

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

@elmanu

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

http://macstrac.blogspot.co.at/2009/04/scala-as-long-term-replacement-for.html
@elmanu

@elmanu

ThoughtWorks TechRadar May 2013
http://www.thoughtworks.com/radar

SCALA IN THE WILD

etc.
@elmanu

SCALA IN THE WILD

@elmanu

SCALA IN THE WORLD

http://www.scala-tribes.org/
@elmanu

SCALA IN VIENNA
• Scala Vienna
•1

User Group

year old, 124+ members

• http://scala-vienna.org/

@elmanu

AVOIDING THE BILLIONDOLLAR 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

@elmanu

AVOIDING THE BILLIONDOLLAR 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")

@elmanu

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) {
!
this.name = 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() {
!
}

}

@elmanu

CONCISENESS
class
var
var
var

User(
name: String,
surname: String,
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

@elmanu

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.name = name;
!
!
this.email = email;
}

!
!
!

public String getName() {
!
return this.name;
}

!
!
!

public String getSurname() {
!
}

!
!
!

public String getEmail() {
!
}

!

@Override public int hashCode() {

!
!

!
}

!

@Override public boolean equals(Object that) {

!

!

!

}

}

@elmanu

// yada yada yada

// 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)

@elmanu

USEFUL TYPE INFERENCE

@elmanu

USEFUL TYPE 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))

@elmanu

EXPLICIT TYPING
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))

@elmanu

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;
! ! }
! }
});

@elmanu

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

@elmanu

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

@elmanu

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

@elmanu

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);
! }
}

@elmanu

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

@elmanu

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

@elmanu

EXTENSIBLE LANGUAGE

• Minimal

language, powerful library

• Language

@elmanu

features for extensibility

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()
}
}
}
@elmanu

MACROS

• Compile-time, during
• Expanding

type checking

the AST

• Experimental

since Scala 2.10

http://scalamacros.org
@elmanu

MACROS
PLAY JSON DE/SERIALIZATION

@elmanu

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))

@elmanu

MACROS

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

@elmanu

IDE

• IntelliJ

IDEA

• Eclipse
• SublimeText

@elmanu

SIMPLE BUILD TOOL
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

@elmanu

PLAY! FRAMEWORK
• MVC

web framework,
inspired by RoR and Django

• Java, Scala
• Everything

is compiled

& scalable
performance

• Predictable

• Fun

to work with!

@elmanu

AKKA
• Toolkit

for building
concurrent & distributed
applications more easily

• Actors

as concurrency
model, simpler to reason
with than threads

• Remoting

and
clustering support
@elmanu


REACTIVE

http://www.reactivemanifesto.org


THANK YOU!

Questions, comments ?
http://manuel.bernhardt.io
manuel@bernhardt.io
@elmanu

@elmanu

FRAMEWORKS: AKKA
• Actor

concurrency model based on Erlang

• “Human” design: actors

hierarchies

• Much, much, much

threads

@elmanu

talk to eachother and form

simpler to work and reason with than

FRAMEWORKS: AKKA

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

@elmanu

FRAMEWORKS: AKKA
class Master extends Actor {
!

val workers = context.actorOf(Props[Worker].withRouter(
! RoundRobinRouter(nrOfInstances = 5))
! )
!
!
!
!
!

case Start =>
! getDocumentsFromDb.foreach { document =>
! ! workers ! Process(document)
! }

!
!

case Result(processed) =>
! writeResult(processed)

!
!

!
!

case Stop =>
! children.foreach(stop)

!
}


!
!
!
!

!
!

@elmanu

def receive = {

}

FRAMEWORKS: AKKA
class Worker extends Actor {
! def receive = {
!
!
!
!
}

@elmanu

! case Process(doc: Document) =>
! ! val processed = doSomeHardWork(doc)
! ! sender ! Result(processed)
}

FRAMEWORKS: PLAY

• MVC

framework à la Rails

• Everything
•I

is compiled

mean everything: CSS, JavaScripts, Templates, URLs, JSON, ...

@elmanu

FRAMEWORKS: PLAY
GET
POST
PUT
DELETE

@elmanu

/users
/users
/users/:id/update
/users/:id

controllers.Users.list
controllers.Users.create
controllers.Users.update(id: Long)
controllers.Users.delete(id: Long)

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

@elmanu

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

@elmanu

200 OK
Content-Type: application/json

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