An introductory talk on Scala at the joint meeting of Java User Group Scotland and Scala Scotland in Edinburgh on 28 September 2010

1. Scala coated JVM
@ Joint meeting of Java User Group Scotland
and Scala Scotland
Stuart Roebuck
stuart.roebuck@proinnovate.com

2. The basics…
• Created by Martin Odersky (EPFL)
• JVM
• Object oriented and functional
• ‘scalable language’
• Scala 1.0—late 2003
• Scala 2.8.0—July 2010

3. “If I were to pick a language to
use today other than Java, it
would be Scala”
James Gosling

4. Commercial users of Scala
• Twitter—Scala back end Ruby front end
• LinkedIn
• Foursquare—Scala and Lift
• Siemens—Scala and Lift
• SAP
• EDF
• Sony Pictures (ImageWorks)
• Nature Magazine
• TomTom
• …and Google

5. Try this at home!
• Scala home: http://www.scala-lang.org/
• Downloadable for Mac, Linux & Windows
• Shell interpreter: scala
• Compilers: scalac and fsc
• Documentation generator scaladoc
• Plugins for Eclipse, Netbeans, IntelliJ
• Popular build tool “sbt” (simple-build-tool)

6. Demo 1
Scripting with Scala

7. Email extraction shell script
#! /bin/sh
exec scala "$0" "$@"
!#
import scala.io.Source
val email = """[a-zA-Z0-9._%+-]+@[a-zA-Z0-9.-]+.[a-zA-Z]{2,4}""".r
val filtered = Source.stdin.getLines.
flatMap( email.findAllIn(_)).
map(_.toLowerCase).toSet.toList.sortWith(_<_)
filtered.foreach{ println(_) }

8. How does Scala differ
from Java?
• Everything is an object • Pattern matching and
Extractors
• First-class functions
(‘closures’) • XML literals
• Singleton objects • Case classes
• Mixin composition • Lazy evaluation
with Traits • Tuples

9. Everything is an object
“Answer = ” + 6 * 4
“Answer = ”.+((6).*(4))

10. First class functions
def time(f: => Unit): Double = {
val start = System.nanoTime
f
val end = System.nanoTime
(end - start) / 1000000.0
}
val timeTaken = time {
Thread.sleep(100)
}

11. Singleton Objects (Java)
public class Singleton {
private Singleton() {
}
private static class SingletonHolder {
public static final Singleton INSTANCE = new Singleton();
}
public static Singleton getInstance() {
return SingletonHolder.INSTANCE;
}
}

12. Singleton Objects (Scala)
object Singleton {
val name = “This is a Singleton Object”
}

13. Traits / Mix-in Composition
class Executor(f: () => Unit) {
def exec() { f() }
}
trait Logging extends Executor {
override def exec() {
println("Executing...")
super.exec()
}
}
trait Timing extends Executor {
override def exec() {
val start = System.currentTimeMillis
super.exec()
val end = System.currentTimeMillis
printf("==> Time taken: %d ms%n", end-start)
}
}
val e = new Executor(() => println("Hello")) with Timing with Logging
e.exec
Executing...
Hello
==> Time taken: 0 ms

14. Pattern Matching
def intToString(value: Any) = value match {
case x:Int => x.toString
case (x:Int) :: y => x.toString
case Some(x:Int) => x.toString
case _ => ""
}
scala> intToString(23)
res1: java.lang.String = 23
scala> intToString(List(23,45))
res2: java.lang.String = 23
scala> intToString(Some(11))
res3: java.lang.String = 11
scala> intToString(Some("String"))
res4: java.lang.String =

15. Demo 2
e Scala REPL(Read Eval Print Loop)

16. BigInteger / BigInt Factorial
import java.math.BigInteger
def factorial(x: BigInteger): BigInteger =
if (x == BigInteger.ZERO)
BigInteger.ONE
else
x.multiply(factorial(x.subtract(BigInteger.ONE)))
def factorial(x: BigInt): BigInt =
if (x == 0) 1 else x * factorial(x - 1)

17. BigInt Definition
class BigInt(val bigInteger: BigInteger) extends java.lang.Number {
override def hashCode(): Int = this.bigInteger.hashCode()
override def equals (that: Any): Boolean = that match {
case that: BigInt => this equals that
case that: java.lang.Double => this.bigInteger.doubleValue == that.doubleValue
case that: java.lang.Float => this.bigInteger.floatValue == that.floatValue
case that: java.lang.Number => this equals BigInt(that.longValue)
case that: java.lang.Character => this equals BigInt(that.charValue.asInstanceOf[Int])
case _ => false
}
def equals (that: BigInt): Boolean = this.bigInteger.compareTo(that.bigInteger) == 0
def compare (that: BigInt): Int = this.bigInteger.compareTo(that.bigInteger)
def <= (that: BigInt): Boolean = this.bigInteger.compareTo(that.bigInteger) <= 0
def >= (that: BigInt): Boolean = this.bigInteger.compareTo(that.bigInteger) >= 0
def < (that: BigInt): Boolean = this.bigInteger.compareTo(that.bigInteger) < 0
def > (that: BigInt): Boolean = this.bigInteger.compareTo(that.bigInteger) > 0
def + (that: BigInt): BigInt = new BigInt(this.bigInteger.add(that.bigInteger))
…

18. Implicit conversion
scala> factorial(10)
res0: BigInt = 3628800
implicit def int2bigInt(i: Int): BigInt = BigInt(i)
def factorial(x: BigInt): BigInt = …
scala> factorial(int2bigInt(10))
res0: BigInt = 3628800

19. Pattern matching
scala> val Email = """([a-zA-Z0-9._%+-]+)@([a-zA-Z0-9.-]+.[a-zA-Z]
{2,4})""".r
Email: scala.util.matching.Regex = ([a-zA-Z0-9._%+-]+)@([a-zA-
Z0-9.-]+.[a-zA-Z]{2,4})
scala> val Email(name,address) = "stuart.roebuck@proinnovate.com"
name: String = stuart.roebuck
address: String = proinnovate.com

20. Demo 3
Building a Scala project with sbt

22. Questions?

24. Build tools +
• Maven Plugin (no endorsement implied)—http://
scala-tools.org/mvnsites/maven-scala-plugin/
• simple-build-tool—http://code.google.com/p/
simple-build-tool/
• Apache Ant tasks for Scala—http://www.scala-
lang.org/node/98
• Apache Buildr—http://buildr.apache.org/
• JavaRebel—http://www.zeroturnaround.com/
jrebel/