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First Introduction to Scala

A brief tour of the major features of the next big JVM language

Alan Raison

on 29 January 2013

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Transcript of First Introduction to Scala

Scala What is Scala? Object Oriented
Strongly, Statically typed
Compiled to JVM bytecode
"Scalable" Alan Raison a first introduction Start it Up! > scala Scala IDE IntelliJ val x = 4 def incr(x: Int) =
x + 1 def test = {
if (incr(x) == 5) {
} else {
} Classes class LockManager extends MyBaseClass {
var locksInUse = 0
def take = {
locksInUse = locksInUse + 1
def release = {
locksInUse = locksInUse - 1
println("LockManager ready")
} (not functional style) A Java Bean public class PersonImpl implements Person {
private String firstname;
private String surname;
public PersonImpl(String firstname, String surname) {
this.firstname = firstname;
this.surname = surname;
public String getFirstname() {
return this.firstname;
public void setFirstname(String firstname) {
this.firstname = firstname;
public String getSurname() {
return this.surname;
public void setSurname(String surname) {
this.surname = surname;
} A Scala "Bean" class Person(firstname: String, surname: String) Case Classes A class definition with some added extras:
Generated toString, equals, hashcode methods
Generated companion object
Can be used in match expressions case class Person(firstname: String, surname: String) (try it!) val alan = new Person("Alan", "Raison") Companion Objects Singleton objects, often providing factory or utility methods to the companion class object Person {
def teenager = // construct a teenager
def adult = // construct an adult
} like Java's class variables and methods (some) core language elements Traits Feature-rich Interfaces Question: What can Java interfaces contain? public interface MyInterface extends Superinterface1, Superinterface2 {
static String CONSTANT = "1234567890";
void providesBehaviour(String name, Object argument);
} What if they could have default implementations? <T> int compareTo(T other) {
//return <0 if other is less than this
//return 0 if equal
//return >0 if other is more
} trait ComparableTrait[T] {
def compare(other: T): Int } def >=(that: T): Boolean = this > that || this == that def <=(other: T): Boolean = this.<(other) || this.==(other) def ==(other: T): Boolean = compare(other) == 0
def <(other: T): Boolean = compare(other) < 0
def >(other: T): Boolean = compare(other) > 0 class Rational(numer: Int, denom: Int) extends ComparableTrait[Rational] {
def compare(other: Rational) =
(this.numer * other.denom) - (other.numer * this.denom)
} new Rational(3, 4) < new Rational(2, 3)
new Rational(2,3) == new Rational(4,6) Pattern Matching Case classes can be used in match expressions: case class Person(firstname: String, surname: String)

e match {
case Person("Alan", _) => println("What a great name!")
case Person("Philip", surname) => println("Hi Phillys " + surname)
case Person(first, sur) => println("Hi " + first + " " + sur)
case _ => println("Not a person")
} Options Used to distinguish between Something and Nothing! abstract class Option[T]
case class Some[T](val: T)
case object None def mightReturnInt(): Option[Int]

mightReturnInt() match {
case Some(i) => println("found " + i)
case None => println("nothing")
} No NullPointerExceptions here! Integrating With Java Since it's a JVM language, it's easy! import javax.swing.{JButton, WindowConstants, JFrame}

object Application {
def main() {
val frame = new JFrame("Swing in Scala!")
frame.add(new JButton("Button"))
} An Example var y = 5
y = y + x
// x = 3 : not possible A Car Showroom Create a Car class with suitable properties
Create some single object instances of the class Create a "CarShowroom" object,
provide a method to list all Cars Create methods which filter the list to certain criteria Function Literals Functions can be passed as arguments, or assigned to variables (x: Class1, y: Class2, ...) => expression (x: Int, y: Int) => x + y List.apply("One", "Two", "Three") // or simply
List("One", "Two", "Three") case class Car(make: String, model: String, doors: Int) object CarShowroom {
def allCars = List(HondaCivic, FordFocus, PorscheBoxter)

def minDoors(number: Int) = allCars.filter( c =>
c.doors >= number) Created by Martin Odersky
Also responsible for current javac,
Java Generics
Created to make Functional Programming practical
Now owned by Typesafe who also develop Akka and the Play! Framework
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