If I were to pick a language to use on the JVM today other than
Java, it would be Scala.
James Gosling, creator of
Javahttp://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
leadhttp://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
Groovyhttp://macstrac.blogspot.com/2009/04/scala-as-long-term-replacement-for.html
Agenda
Background and motivation
Intro to ScalaBasic syntax
Pattern matching
Functions
Classes and traits
Practical Scala
About us
Alf Kristian Style and Fredrik Vraalsen
Java developers with 6 and 9 years experience
Scala enthusiasts since 2008
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 persons = ... List adults = new LinkedList(); List kids =
new LinkedList();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
Statically typed
Java compatibleCompiles 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)// orangemap(2)// twoarray(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
"[email protected]" 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 even = new Predicate() {@Overridepublic boolean
apply(Integer i) {return i % 2 == 0;}};
List numbers = // 1, 2, 3, 4Iterable 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 even = new Predicate() {@Overridepublic 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 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 = 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 // trueperson1 = 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
Loudprintln(person)
=> MY NAME IS FREDRIK
Just scratching the surface...
Tuples
Singleton objects
Closures
For-comprehensions
Implicit conversions
Actors
Native XML data types
Parsers
Q & A
val xml =
Practical Scala
The downside
Tools
ScalaTest
Java interoperability
Learning curve
Your choiceFunctional programming
Implicit conversions
Higher order functions
IDE support
Netbeans - very good, but inferior in other areas
IntelliJ IDEA - very good, but slow compilation
Eclipse - bad, but very fast when working
Backward compatibility
Binary compatibility broken several times
Think twice before using a library
Tools demo
REPL - Read eval print loop
Maven
SBT - Simple Build Tool
IntelliJ IDEA
JRebel
"Complete Java projects 10-23 % faster"
Hotswap on steroids
Commercial, but free for Scala
ScalaTest demo
DSL for testing
Powerful assertions
Different test stylesJUnit
Functional tests
BDD test
The feel of Scala
http://parleys.com/#id=10&st=5&sl=1
Java interoperability demo
Scala using Java
Java using Scala
Mixed projects?
Learning curve
Syntax small smack in the face
Easy to write Java-ish Scala
The language scales with your understanding
Gradually migrate to more functional style
What would you like to hear?
Functional programmingWhat is it all about?
Implicit conversionWhy does "gnirtS.gnal.avaj".reverse work?
Higher order functionsHow does the using/resource handling
example work?
Functional programming
First class functions
Pattern matching
Higher order functions
Functional programming
Mathematical functions have no side effects
f(x) = 2x + 3
In practice
Only immutable objects (and object graphs)All field must be
immutable
No side-effects from method calls
All methods must return something
Example scala.List
head :: tail
val list = List(1, 2)val myList = 1 :: 2 :: Nil
// 0 :: 1 :: 2 :: Nilval myotherList = 0 :: myList
scala.collection.immutable
...or scala.collection.mutable
Pick your poison!
Strive to be pure
Concurrency
Easier to avoid errors
Easier to test
We have a lot to learn
Q & A
Resources
[email protected] (http://lister.java.no/mailman/listinfo/scala)
http://scala.java.no
http://www.slideshare.net/stoyle/scala-intro
http://github.com/stoyle/javaBin-demo
[email protected], [email protected]
