Scala introduction

If I were to pick a language to use on the JVM today other than Java, it would be Scala. – James Gosling, creator of Java http://www.adam-bien.com/roller/abien/entry/java_net_javaone_which_programming Scala, it must be stated, is the current heir apparent to the Java throne. No other language on the JVM seems as capable of being a "replacement for Java" as Scala, and the momentum behind Scala is now unquestionable. – Charlies Nutter, JRuby lead http://blog.headius.com/2009/04/future-part-one.html My tip though for the long term replacement of javac is Scala. I'm very impressed with it! I can honestly say if someone had shown me the Programming in Scala book […] back in 2003 I'd probably have never created Groovy. – James Strachan, creator of Groovy http://macstrac.blogspot.com/2009/04/scala-as-long-term-replacement-for.html

Agenda Background and motivation

About us Alf Kristian Støyle and Fredrik Vraalsen

Java developers with 6 and 9 years experience

Developed SubmitIT for JavaZone

Alf worked on Scala application for Kommuneforlaget

Held 4 Scala training courses for 60+ participants

public class Person { private int age ; private String name ; public Person( int age, String name) { this . age = age; this . name = name; } public int getAge() { return this . age ; } public void setAge( int age) { this . age = age; } public String getName() { return this . name ; } public void setName(String name) { this . name = name; } } class Person ( var age : Int , var name : String )

List<Person> persons = ... List<Person> adults = new LinkedList<Person>(); List<Person> kids = new LinkedList<Person>(); for (Person person : persons) { if (person.getAge() < 18) { kids.add(person); } else { adults.add(person); } } val persons : List [ Person ] = ... val ( kids , adults ) = persons . partition (_. age < 18)

using ( new BufferedReader ( new FileReader ( "f.txt" ))) { reader => println ( reader . readLine() ) } BufferedReader reader = null ; try { reader = new BufferedReader( new FileReader( "f.txt" )); System. out .println(reader.readLine()); } finally { if (reader != null ) { try { reader.close(); } catch (IOException e) { // Exception on close, ignore } } }

Scala Object oriented and functional

Java compatible Compiles to Java bytecode

Existing libraries/frameworks Better Java

public class Person { private int age ; private String name ; public Person( int age, String name) { this . age = age; this . name = name; } public int getAge() { return this . age ; } public void setAge( int age) { this . age = age; } public String getName() { return this . name ; } public void setName(String name) { this . name = name; } }

public class Person { private int age private String name public Person( int age, String name) { this . age = age this . name = name } public int getAge() { return this . age } public void setAge( int age) { this . age = age } public String getName() { return this . name } public void setName(String name) { this . name = name } }

Variables var i : Int = 42

Variables var i = 42 i = 3 i = "Hello world!" // compile error

Values val i = 42 i = 3 // compile error

Methods def sum ( a : Int , b : Int ): Int = { return a + b }

Methods def sum ( a : Int , b : Int ): Int = { a + b }

Methods def sum ( a : Int , b : Int ) = { a + b }

Methods def sum ( a : Int , b : Int ) = a + b

Methods def sayHello ( name : String ) { println ( "Hello, " + name ) }

Methods "apple" . charAt (0) "apple" charAt 0 1.0.+(2.0) 1.0 + 2.0

Collections val list = List ( "apple" , "orange" , "banana" ) val map = Map (1 -> "one" , 2 -> "two" ) val array = Array (1, 2, 3, 4, 5) list (1) // orange map (2) // two array (3) // 4

myObject match { case 1 => println ( "First" ) case 2 => println ( "Second" ) case _ => println ( "Unknown" ) } Pattern matching

myObject match { case i : Int => println ( "Found number " + i ) case s : String => println ( "Found text " + s ) case _ => println ( "Unknown" ) } Pattern matching

val email = """ (.+) @ (.+) """ . r " scala @ java.no " match { case email ( name , domain ) => println ( "User " + name + " at " + domain ) case x => println ( x + " is not an email" ) } Pattern matching

val numbers = List (1, 2, 3) val secondNumber = numbers match { case List (_, i , _*) => Some ( i ) case _ => None } => secondNumber : Option [ Int ] = Some (2) Pattern matching

Functions Predicate <Integer> even = new Predicate <Integer>() { @ Override public boolean apply(Integer i) { return i % 2 == 0; } }; List<Integer> numbers = … // 1, 2, 3, 4 Iterable<Integer> evenNums = Iterables .filter(numbers, even); => [2, 4] Google collections:

Functions val even = ( i : Int ) => i % 2 == 0 val numbers = List (1, 2, 3, 4) val evenNums = numbers . filter ( even ) => List(2, 4) Scala collections:

Functions val numbers = List (1, 2, 3, 4) val evenNums = numbers . filter (( i : Int ) => i % 2 == 0) => List(2, 4) Scala collections:

Functions val numbers = List (1, 2, 3, 4) val evenNums = numbers . filter ( i => i % 2 == 0) => List(2, 4) Scala collections:

Functions val numbers = List (1, 2, 3, 4) val evenNums = numbers . filter (_ % 2 == 0) => List(2, 4) Scala collections:

Functions Predicate <Integer> even = new Predicate <Integer>() { @ Override public boolean apply(Integer i) { return i % 2 == 0; } }; val numbers = List (1, 2, 3, 4) val evenNums = numbers . filter (_ % 2 == 0) => List(2, 4) Scala collections:

Functions #boolean(int) even = #(int i)(i % 2 == 0) JDK7 lambda expressions: val even = ( i : Int ) => i % 2 == 0 Scala functions:

Functions Iterables.filter(numbers, #(int i)(i % 2 == 0)) JDK7 lambda expressions: numbers . filter (_ % 2 == 0) Scala functions:

Control structures return values val numbers = for ( i <- 1 to 10) yield i val res = if ( cond ) x else y val res2 = try { x } catch { … y } finally { … }

Classes and constructors class Person ( val age : Int )

Classes and constructors class Person ( val age : Int ) { def this () = this (42) var name : String = _ override def toString = "My name is " + name }

Traits (= Interface + Mixin) “Multiple inheritance done right”

Call to super -> strict semantics

scala.Ordered trait trait Ordered [ A ] { def compare ( that : A ): Int def < ( that : A ): Boolean = ( this compare that ) < 0 def > ( that : A ): Boolean = ( this compare that ) > 0 def <= ( that : A ): Boolean = ( this compare that ) <= 0 def >= ( that : A ): Boolean = ( this compare that ) >= 0 }

The Ordered trait class Person ( val age : Int ) extends Ordered [ Person ] { def compare ( other : Person ) = this . age - other . age } val person1 = new Person (21) val person2 = new Person (31) person1 < person2 // true person1 <= person2 // true person1 >= person2 // false

“Dynamic mixins” class Person ( val name : String, val age : Int ) { override def toString = "My name is " + name } trait Loud { override def toString = super . toString . toUpperCase } val person = new Person ( "Fredrik" , 18) with Loud println ( person ) => MY NAME IS FREDRIK

Just scratching the surface... Tuples

Scala introduction

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