The document discusses Scala, a scalable programming language created by Martin Odersky, emphasizing its object-oriented and functional programming capabilities. It outlines Scala's differences from Java, including features like pattern matching, first-class functions, and mixins. Additionally, it mentions commercial users of Scala and provides resources and examples for getting started with the language, including installation and scripting demos.

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/