scala - java2days sofia

SCALAJava2Days 2013

Manuel Bernhardt

Dienstag, 03. Dezember 13

@elmanu

AGENDA

• History

• Why Scala?

• Scala in the wild

• The Code / Scala in practice

• Tools & more


@elmanu

YOUR SPEAKER

• Independent software consultant based in Vienna

• Web, web, web

• Scala & Java & Javascript

• Open-Source


@elmanu

AGENDA

• History

• Why Scala?



• Tools & more


@elmanu

HISTORY

• Martin Odersky, EPFL

• Espresso, Pizza, GJ, javac

• Funnel, Scala

• First Scala release in 2003


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AGENDA

• History

• Why Scala?




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SCALA DESIGN GOALS


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SCALA DESIGN GOALS

• Full interoperability with Java


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SCALA DESIGN GOALS


• Cut down boilerplate


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SCALA DESIGN GOALS



• Pure object orientation & functional programming


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SCALA DESIGN GOALS




• Move away from null


@elmanu

SCALA DESIGN GOALS




• Move away from null

• Multi-core programming


@elmanu

AGENDA

• History

• Why Scala?



• Tools & more


@elmanu

WHAT PEOPLE SAY

If I were to pick a language todayother than Java, it would be Scala.

James GoslingFather of Java


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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 StrachanCreator of Groovy

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




@elmanu

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


http://www.thoughtworks.com/radar

http://www.thoughtworks.com/radar

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SCALA IN THE WILD

etc.


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SCALA IN THE WILD


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SCALA IN THE WORLD

http://www.scala-tribes.org/Dienstag, 03. Dezember 13

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SCALA IN VIENNA

• Scala Vienna User Group

• 1 year old, 124+ members

• http://scala-vienna.org/


http://scala-vienna.org/

http://scala-vienna.org/

@elmanu

AGENDA

• History

• Why Scala?



• Tools & more


@elmanu

AVOIDING THE 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


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AVOIDING THE 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")


@elmanu

CONCISENESSpublic 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) {! ! this.surname = surname;! }

! public void setEmail(String email) {! ! this.email = email! }

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

! public String getSurname() {! ! return this.surname;! }

! public String getEmail() {! ! return this.surname;! }

}


@elmanu

CONCISENESSclass User( var name: String, var surname: String, var email: String)

val bob = new User("Bob", "Marley", "[email protected]")// bob: User = User@5c3f1224

bob.name // res0: String = Bob

bob.name = "Bobby" // bob.name: String = Bobby


@elmanu

CONCISENESSpublic 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.surname = surname;! ! this.email = email;! }

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

! public String getSurname() {! ! return this.surname;! }

! public String getEmail() {! ! return this.surname;! }

! @Override public int hashCode() {

! ! // yada yada yada! }

! @Override public boolean equals(Object that) {

! ! // yada yada yada

! }

}


@elmanu

CONCISENESScase class ImmutableUser( name: String, surname: String, email: String)

val bob = ImmutableUser("Bob", "Marley", "[email protected]")// 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)


mailto:[email protected]


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USEFUL TYPE INFERENCE


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USEFUL TYPE INFERENCEval 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 TYPINGval 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 STYLEusers.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

COLLECTION LIBRARY & FUNCTIONAL STYLE

def sortByAge(user1: User, user2: User) = user1.age > user2.age

users.sortWith(sortByAge)


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


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


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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


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


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


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• Minimal language, powerful library

• Language features for extensibility

EXTENSIBLE LANGUAGE


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DOMAIN SPECIFIC LANGUAGES

import collection.mutable.Stackimport 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 type checking

• Expanding the AST

• Experimental since Scala 2.10

http://scalamacros.org




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MACROSPLAY JSON DE/SERIALIZATION


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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


import play.api.json._

implicit val creatureFormat = Json.format[Creature] // format is a macro


@elmanu

AGENDA

• History

• Why Scala?



• Tools & more


@elmanu

IDE

• IntelliJ IDEA

• Eclipse

• SublimeText


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SIMPLE BUILD TOOLname := "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

• Predictable & scalable performance

• 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


REACTIVE

http://www.reactivemanifesto.org




@elmanu

THANK YOU!

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

[email protected]

@elmanu


http://manuel.bernhardt.io

http://manuel.bernhardt.io



@elmanu

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


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FRAMEWORKS: AKKA

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


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

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

@elmanu

FRAMEWORKS: AKKAclass 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)

! }}


@elmanu

FRAMEWORKS: AKKA

class Worker extends Actor {

! def receive = {

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

}


@elmanu

FRAMEWORKS: PLAY

• MVC framework à la Rails

• Everything is compiled

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


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FRAMEWORKS: PLAY

GET /users controllers.Users.listPOST /users controllers.Users.createPUT /users/:id/update controllers.Users.update(id: Long)DELETE /users/:id controllers.Users.delete(id: Long)


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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)) }

}200 OK

Content-Type: application/json


scala - java2days sofia

Technology

elmanu dienstag

private string surname

private string email

public string getname

public string getsurname

public string getemail

private final string

private final string