scala - en bedre java?

- en bedre Java?

Jesper Kamstrup Linnetjesper@linnet-data.dk

Community Day 201027. maj 2010

Om mig

•Freelancekonsulent

•Java- og .NET-udvikler/arkitekt

•Sprogbegejstret

Agenda

•Hvad er Scala?

•En bedre Java?

•Ready for prime time?

Er Java dødt som sprog?

Kilde: InfoQ.com

Hvis Java var en bil...

Hvad er Scala?

Kort om Scalas historie

•Startet i 2001

•Skabt af Martin Odersky

Kendetegn

•Statisk typet

•Hybridsprog

•Skalabilitet i højsædet

Java-kompatibelt

• Eksisterende Java API’er

• Afvikles på JVM’en

• Genererer .class-filer

Hvis Scala var en bil...

=Objektorienteret

+Funktionsorienteret

Hybridsprog

Objektorienteret

1.to(5) Range(1, 2, 3, 4, 5)

Funktionsorienteret

val a = 10

val f = (x: Int) => x + 5

Immutability

• Centralt i funktionsprogrammering

• Vigtigt for parallelisering

• Letter kodelæsning

Hvad gør Scala mere effektivt?

Image: Suat Eman / FreeDigitalPhotos.net

Syntaktisk sukker

Hello, world

println("Hello, world")

Kompakt syntaks (1)

public class Person { private final String name; private final String address;

public Person(String name, String address) { this.name = name; this.address = address; }

public String getName() { return name; }

public String getAddress() { return address; }

Javaclass Person( val name: String, val address: String);

Scala

Kompakt syntaks (2)

public class Person { private final String name; private final String address;

public Person(String name, String address) { this.name = name; this.address = address; }

public String getName() { return name; }

public String getAddress() { return address; }

@Override public int hashCode() { ... }

@Override public boolean equals(Object obj) { ... }

@Override public String toString() { ... }

Java Scalacase class Person( name: String, address: String);

Kompakt syntaks (3)

class Car { var driven = 0.0 def drive(distance: Double) = driven += distance def milesDriven = driven * 1.6}

...

val car = new Carcar drive 10

copy methodSca

la 2.8

val person = Person("Jesper", "Kbh")

Person(Jesper,Aarhus)

val newPerson = person.copy(address = "Aarhus")

Collections

val list = List(1,2,3)val map = Map("Jesper" -> 39,"Peter" -> 55)val set = Set(1, 2, 5, 2)val array = Array(1, 2, 3)

Hvad foretrækker du?

List<Integer> numbers = ...

List<Integer> result = new ArrayList<Integer>();for (Integer number : numbers) { if (isEven(number) { result.add(number); }}

Java Scalaval numbers = ...

val result = numbers filter isEven

Anonyme funktioner

val list = List(1,2,3,4)

List(2, 4)

list filter { _ % 2 == 0 }

list filter isEven

list filter { n => n % 2 == 0 }

Eksempler

val list = List(1,2,3,4)

list map (x => x * x) List(1, 4, 9, 16)

list sum 10

list mkString "," 1,2,3,4

list forall { _ < 5 } true

list partition isEven (List(2, 4),List(1, 3))

Pattern matching (1)

case "test" => println("Streng")

value match {case 1 => println("Tal")case i: Int => printf("Tallet %d", i)

case (x, y) => printf("Et par, x=%s, y=%s", x, y)case _ => println("Alt andet")

}

Pattern matching (2)

value match {

case List(1, rest @ _*) => println("1 og flere")case List(_, _) => println("To elementer")

}

Lister

Pattern matching (3)

val Danish = "Hej (.*)".rval English = "Hi, (.*)".r

greeting match { case Danish(name) => printf("Dansk: %s", name) case English(name) => printf("Engelsk: %s", name)}

Regulære udtryk

Pattern matching (4)

value match { case Person(_, "Kbh") => println("Københavner") case _ => println("Uden for København")}

Case classes

XML (1)

val personsXml = <persons> <person name="Jesper"><age>38</age></person> <person name="Ulla"><age>{age}</age></person> </persons>

XML (2)

val names = personsXml \\ "@name"

val persons = personsXml \ "person"

val name = person \ "@name"

XML (3)

node match { case <name>{name}</name> => println(name) case _ => println("Andet")}

Duck typing

“If it walks like a duck, and quacks like a duck, then it is a duck”

Duck typing

public class Text extends ... { public void setText (String string) {

public class Button extends ... { public void setText (String string) {

Duck typing m. Scala

def update(control: { def setText(text: String) }) = { control.setText("Hello, world")}

type ControlWithText = { def setText(text: String) }

def update(control: ControlWithText) = { control.setText("Hello, world")}

Traits (1)

trait Editable { def isEditable(): Boolean}

class EditablePerson extends Editable { def isEditable() = true}

Som interface

Traits (2)

Definition af mixin

trait Persistable { val entityManager: EntityManager = ...

def save = { entityManager.persist(this) }}

Traits (3)

Statisk brug af mixin

class Car extends Vehicle with Persistable { ...}

val car = new Carcar.save

Traits (4)

Dynamisk brug af mixin

class Bicycle extends Vehicle { ...}

val bicycle = new Bicycle with Persistablebicycle.save

Traits (5)

Overstyring trait LoggingCollection extends

java.util.Collection[String] {

abstract override def add(e: String) = { printf("Adding: %s", e) super.add(e) }}

val coll = new java.util.ArrayList[String] with LoggingCollection

Traits (6)

Eksempel: Observer trait Subject { type Observer = { def receiveUpdate(subject:Any) }

private var observers = List[Observer]()

def addObserver(observer:Observer) = observers ::= observer

def notifyObservers = observers foreach (_.receiveUpdate(this))}

Parallelisering

•Højere abstraktionsniveau

•Aktørmodel

•Beskedudveksling

•Share-nothing

Simpel aktør

import scala.actors.Actor._

actor { calculateStuff}

// stuff in main thread

Beskedudveksling

val parrot = actor { while (true) { receive { case msg => println("Msg: " + msg) } }}

parrot ! "Hello, Polly"

Ready for prime time?

Scala i den virkelige verden

Masser af information

•http://scala-lang.org

•Bøger

•Tutorials og artikler

Hvorfor ikke Scala?

•Ny syntaks

•“Ungt” sprog

•Værktøjsunderstøttelse

Hvorfor Scala?

•Kompatibilitet med Java

•Stærkere syntaks

•I fremgang

Hvorfor Scala?

“You only fully comprehend the awesomeness of #scala when after weeks of being pure scala you have to edit some Java again...”

James Strachan (@jstrachan)

En bedre Java?Java Scala

Java++ ?

Konklusion

En bedre og mere effektiv Java?

Spørgsmål?

Kontakt

•Slides: http://bit.ly/scala-cd10

• jesper@linnet-data.dk

• http://twitter.com/jesper_linnet

• http://blog.kamstrup-linnet.dk