Scala is an acronym for “Scalable Language”. This means that Scala grows with you. You can play with it by typing one-line expressions and observing the results. But you can also rely on it for large mission critical systems, as many companies, including Twitter, LinkedIn, or Intel do.
Object-Oriented Meets Functional
Have the best of both worlds. Construct elegant class hierarchies for maximum code reuse and extensibility, implement their behavior using higher-order functions. Or anything in-between.
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You can download Scala from Official Download.
If you are a user of OSX, you als can install Scala using brew:
$ brew install scala
$ scala
scala> println("Hello world")
Hello world
scala> 1 + 1
res1: Int = 2
scala> (1).+(1)
res2: Int = 2
scala> 1 + 1.0
res3: Double = 2.0
scala> 1 + 2 * 3
res4: Int = 7
scala> 1.+(1)
res5: Int = 2
scala> 1.+(2.*(3))
res6: Int = 7
scala> 5.+(4.*(3))
res7: Int = 17
scala> "hello".size
res8: Int = 5
scala> "hello" + 4
res9: String = hello4
scala> 4 + "hello"
res10: String = 4hello
scala> 4 + ".0"
res11: String = 4.0
scala> 4 * "1"
<console>:8: error: overloaded method value * with alternatives:
(x: Double)Double <and>
(x: Float)Float <and>
(x: Long)Long <and>
(x: Int)Int <and>
(x: Char)Int <and>
(x: Short)Int <and>
(x: Byte)Int
cannot be applied to (String)
4 * "1"
^
scala> 1 < 2
res13: Boolean = true
scala> 1 <= 2
res14: Boolean = true
scala> 2 <= 1
res15: Boolean = false
scala> 1 != 2
res16: Boolean = true
scala> a = 1
<console>:10: error: not found: value a
val $ires0 = a
^
<console>:7: error: not found: value a
a = 1
^
scala> val a = 1
a: Int = 1
scala> a = 2
<console>:8: error: reassignment to val
a = 2
^
scala> val b = 2
b: Int = 2
scala> if (b < a) {
| println("true")
| } else {
| println("false")
| }
false
scala> Nil
res18: scala.collection.immutable.Nil.type = List()
scala> if (0) println("true")
<console>:8: error: type mismatch;
found : Int(0)
required: Boolean
if (0) println("true")
^
scala> if (Nil) println("true")
<console>:8: error: type mismatch;
found : scala.collection.immutable.Nil.type
required: Boolean
if (Nil) println("true")
^
while.scala
def whileLoop {
var i = 1
while (i <= 3) {
println(i)
i += 1
}
}
whileLoop
$ scala while.scala
1
2
3
for_loop.scala
def forLoop {
println( "for loop using Java-style iteration" )
for (i <- 0 until args.length) {
println(args(i))
}
}
forLoop
$ scala for_loop.scala hello world
for loop using Java-style iteration
hello
world
ruby_for_loop.scala
def rubyStyleForLoop {
println( "for loop using Ruby-style iteration" )
args.foreach { arg =>
println(arg)
}
}
rubyStyleForLoop
$ scala ruby_for_loop.scala hello world
for loop using Ruby-style iteration
hello
world
scala> val range = 0 until 10
range: scala.collection.immutable.Range = Range(0, 1, 2, 3, 4, 5, 6, 7, 8, 9)
scala> range.start
res0: Int = 0
scala> range.end
res1: Int = 10
scala> range.step
res2: Int = 1
scala> (0 to 10) by 5
res3: scala.collection.immutable.Range = Range(0, 5, 10)
scala> (0 to 10) by 6
res4: scala.collection.immutable.Range = Range(0, 6)
scala> (0 until 10 by 5)
res5: scala.collection.immutable.Range = Range(0, 5)
scala> val range = (10 until 0) by -1
range: scala.collection.immutable.Range = Range(10, 9, 8, 7, 6, 5, 4, 3, 2, 1)
scala> val range = (10 until 0)
range: scala.collection.immutable.Range = Range()
scala> val range = (0 to 10)
range: scala.collection.immutable.Range.Inclusive = Range(0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10)
scala> val range = 'a' to 'e'
range: scala.collection.immutable.NumericRange.Inclusive[Char] = NumericRange(a, b, c, d, e)
scala> person._1
res6: String = Elvis
scala> person._2
res7: String = Presley
scala> person._3
<console>:9: error: value _3 is not a member of (String, String)
person._3
^
scala> val (x, y) = (1, 2)
x: Int = 1
y: Int = 2
scala> val (a, b) = (1, 2, 3)
<console>:7: error: constructor cannot be instantiated to expected type;
found : (T1, T2)
required: (Int, Int, Int)
val (a, b) = (1, 2, 3)
^
scala> class Person(firstName: String, lastName: String)
defined class Person
scala> val jeoygin = new Person("Jeoygin", "Wang")
jeoygin: Person = Person@782830e
compass.scala
class Compass {
val directions = List("north", "east", "south", "west")
var bearing = 0
print("Initial bearing: ")
println(direction)
def direction() = directions(bearing)
def inform(turnDirection: String) {
println("Turning " + turnDirection + ". Now bearing " + direction)
}
def turnRight() {
bearing = (bearing + 1) % directions.size
inform("right" )
}
def turnLeft() {
bearing = (bearing + (directions.size - 1)) % directions.size
inform("left" )
}
}
val myCompass = new Compass
myCompass.turnRight
myCompass.turnRight
myCompass.turnLeft
myCompass.turnLeft
myCompass.turnLeft
$ scala compass.scala
Initial bearing: north
Turning right. Now bearing east
Turning right. Now bearing south
Turning left. Now bearing east
Turning left. Now bearing north
Turning left. Now bearing west
constructors.scala
class Person(first_name: String) {
println("Outer constructor")
def this(first_name: String, last_name: String) {
this(first_name)
println("Inner constructor")
}
def talk() = println("Hi")
}
val bob = new Person("Bob")
val bobTate = new Person("Bob", "Tate")
$ scala constructors.scala
Outer constructor
Outer constructor
Inner constructor
ring.scala
object TrueRing {
def rule = println("To rule them all")
}
TrueRing.rule
employee.scala
class Person(val name: String) {
def talk(message: String) = println(name + " says " + message)
def id(): String = name
}
class Employee(override val name: String,
val number: Int) extends Person(name) {
override def talk(message: String) {
println(name + " with number " + number + " says " + message)
}
override def id():String = number.toString
}
val employee = new Employee("Yoda", 4)
employee.talk("Extend or extend not. There is no try.")
nice.scala
class Person(val name:String)
trait Nice {
def greet() = println("Hello world!")
}
class Character(override val name:String) extends Person(name) with Nice
val flanders = new Character("Ned")
flanders.greet
$ scala nice.scala
Hello world!
scala> def double(x:Int):Int = x * 2
double: (x: Int)Int
scala> double(4)
res2: Int = 8
scala> def double(x:Int):Int = {
| x * 2
| }
double: (x: Int)Int
scala> double(6)
res3: Int = 12
scala> var mutable = "I am mutable"
mutable: String = I am mutable
scala> mutable = "Change me..."
mutable: String = Change me...
scala> val immutable = "I am not mutable"
immutable: String = I am not mutable
scala> immutable = "Can't touch this"
<console>:8: error: reassignment to val
immutable = "Can't touch this"
^
scala> List(1, 2, 3)
res0: List[Int] = List(1, 2, 3)
scala> List("one", "two", "three")
res1: List[String] = List(one, two, three)
scala> List("one", "two", 3)
res2: List[Any] = List(one, two, 3)
scala> List("one", "two", 3)(2)
res3: Any = 3
scala> List("one", "two", 3)(4)
java.lang.IndexOutOfBoundsException: 4
at scala.collection.LinearSeqOptimized$class.apply(LinearSeqOptimized.scala:51)
at scala.collection.immutable.List.apply(List.scala:83)
... 33 elided
scala> List("one", "two", 3)(-1)
java.lang.IndexOutOfBoundsException: -1
at scala.collection.LinearSeqOptimized$class.apply(LinearSeqOptimized.scala:51)
at scala.collection.immutable.List.apply(List.scala:83)
... 33 elided
scala> Nil
res6: scala.collection.immutable.Nil.type = List()
scala> val colors = Set("red", "green", "blue")
colors: scala.collection.immutable.Set[String] = Set(red, green, blue)
scala> colors + "yellow"
res7: scala.collection.immutable.Set[String] = Set(red, green, blue, yellow)
scala> colors - "green"
res8: scala.collection.immutable.Set[String] = Set(red, blue)
scala> colors + Set("black", "white")
<console>:9: error: type mismatch;
found : scala.collection.immutable.Set[String]
required: String
colors + Set("black", "white")
^
scala> colors ++ Set("black", "white")
res10: scala.collection.immutable.Set[String] = Set(blue, green, black, white, red)
scala> colors -- Set("red", "green")
res11: scala.collection.immutable.Set[String] = Set(blue)
scala> Set(1, 2, 3) == Set(3, 2, 1)
res14: Boolean = true
scala> List(1, 2, 3) == List(3, 2, 1)
res15: Boolean = false
scala> val ordinals = Map(0 -> "zero", 1 -> "one", 2 -> "two")
ordinals: scala.collection.immutable.Map[Int,String] = Map(0 -> zero, 1 -> one, 2 -> two)
scala> ordinals(2)
res16: String = two
scala> import scala.collection.mutable.HashMap
import scala.collection.mutable.HashMap
scala> val map = new HashMap[Int, String]
map: scala.collection.mutable.HashMap[Int,String] = Map()
scala> map += 4 -> "four"
res17: map.type = Map(4 -> four)
scala> map += 8 -> "eight"
res18: map.type = Map(8 -> eight, 4 -> four)
scala> map
res19: scala.collection.mutable.HashMap[Int,String] = Map(8 -> eight, 4 -> four)
scala> map += "zero" -> 0
<console>:10: error: type mismatch;
found : (String, Int)
required: (Int, String)
map += "zero" -> 0
^
scala> val list = List("tiger", "cat", "dog")
list: List[String] = List(tiger, cat, dog)
scala> list.foreach(animal => println(animal))
tiger
cat
dog
scala> val animals = Set("tiger", "cat", "dog")
animals: scala.collection.immutable.Set[String] = Set(tiger, cat, dog)
scala> animals.foreach(animal => println(animal))
tiger
cat
dog
scala> val animals = Map("tiger" -> "animal", "cat" -> "animal", "dog" -> "animal")
animals: scala.collection.immutable.Map[String,String] = Map(tiger -> animal, cat -> animal, dog -> animal)
scala> animals.foreach(animal => println(animal))
(tiger,animal)
(cat,animal)
(dog,animal)
scala> animals.foreach(animal => println(animal._1))
tiger
cat
dog
scala> animals.foreach(animal => println(animal._2))
animal
animal
animal
scala> list
res26: List[String] = List(tiger, cat, dog)
scala> list.isEmpty
res27: Boolean = false
scala> Nil.isEmpty
res28: Boolean = true
scala> list.length
res29: Int = 3
scala> list.size
res30: Int = 3
scala> list.head
res31: String = tiger
scala> list.tail
res32: List[String] = List(cat, dog)
scala> list.last
res33: String = dog
scala> list.init
res34: List[String] = List(tiger, cat)
scala> list.reverse
res35: List[String] = List(dog, cat, tiger)
scala> list.drop(1)
res36: List[String] = List(cat, dog)
scala> list
res37: List[String] = List(tiger, cat, dog)
scala> list.drop(2)
res38: List[String] = List(dog)
scala> val words = List("train", "plane", "car", "bike")
words: List[String] = List(train, plane, car, bike)
scala> words.count(word => word.size > 3)
res39: Int = 3
scala> words.filter(word => word.size > 3)
res40: List[String] = List(train, plane, bike)
scala> words.map(word => word.size)
res41: List[Int] = List(5, 5, 3, 4)
scala> words.forall(word => word.size > 2)
res42: Boolean = true
scala> words.exists(word => word.size > 4)
res43: Boolean = true
scala> words.exists(word => word.size > 5)
res44: Boolean = false
scala> words.sortWith((s, t) => s.charAt(0).toLower < t.charAt(0).toLower)
res49: List[String] = List(bike, car, plane, train)
scala> words.sortWith((s, t) => s.size < t.size)
res50: List[String] = List(car, bike, train, plane)
scala> val sum = (0 /: list) {(sum, i) => sum + i}
sum: Int = 6
scala> list.foldLeft(0)((sum, value) => sum + value)
res51: Int = 6
scala> val movies =
| <movies>
| <movie genre="action">Pirates of the Caribbean</movie>
| <movie genre="fairytale">Edward Scissorhands</movie>
| </movies>
movies: scala.xml.Elem =
<movies>
<movie genre="action">Pirates of the Caribbean</movie>
<movie genre="fairytale">Edward Scissorhands</movie>
</movies>
scala> movies.text
res0: String =
"
Pirates of the Caribbean
Edward Scissorhands
"
scala> val movieNodes = movies \ "movie"
movieNodes: scala.xml.NodeSeq = NodeSeq(<movie genre="action">Pirates of the Caribbean</movie>, <movie genre="fairytale">Edward Scissorhands</movie>)
scala> movieNodes(0)
res1: scala.xml.Node = <movie genre="action">Pirates of the Caribbean</movie>
scala> movieNodes(0) \ "@genre"
res2: scala.xml.NodeSeq = action
chores.scala
def doChore(chore: String): String = chore match {
case "clean dishes" => "scrub, dry"
case "cook dinner" => "chop, sizzle"
case _ => "whine, complain"
}
println(doChore("clean dishes"))
println(doChore("mow lawn"))
$ scala chores.scala scrub, dry
whine, complain
factorial.scala
def factorial(n: Int): Int = n match {
case 0 => 1
case x if x > 0 => factorial(n - 1) * n
}
println(factorial(3))
println(factorial(0))
scala> val reg = """^(F|f)\w*""".r
reg: scala.util.matching.Regex = ^(F|f)\w*
scala> println(reg.findFirstIn("Fantastic"))
Some(Fantastic)
scala> println(reg.findFirstIn("not Fantastic"))
None
scala> val reg = "the".r
reg: scala.util.matching.Regex = the
scala> reg.findAllIn("the way the scissors trim the hair and the shrubs")
res5: scala.util.matching.Regex.MatchIterator = non-empty iterator
movies.scala
val movies = <movies>
<movie>The Incredibles</movie>
<movie>WALL E</movie>
<short>Jack Jack Attack</short>
<short>Geri's Game</short>
</movies>
(movies \ "_").foreach { movie =>
movie match {
case <movie>{movieName}</movie> => println(movieName)
case <short>{shortName}</short> => println(shortName + " (short)")
}
}
kids.scala
import scala.actors._
import scala.actors.Actor._
case object Poke
case object Feed
class Kid() extends Actor {
def act() {
loop {
react {
case Poke => {
println("Ow..." )
println("Quit it...")
}
case Feed => {
println("Gurgle..." )
println("Burp..." )
}
}
}
}
}
val bart = new Kid().start
val lisa = new Kid().start
println("Ready to poke and feed...")
bart ! Poke
lisa ! Poke
bart ! Feed
lisa ! Feed
$ scala kids.scala
Ready to poke and feed...
Ow...
Quit it...
Ow...
Quit it...
Gurgle...
Burp...
Gurgle...
Burp...
$ scala kids.scala
Ready to poke and feed...
Ow...
Quit it...
Gurgle...
Burp...
Ow...
Quit it...
Gurgle...
Burp...
sizer.scala
import scala.io._
import scala.actors._
import Actor._
object PageLoader {
def getPageSize(url : String) = Source.fromURL(url).mkString.length
}
val urls = List("http://www.amazon.com/",
"http://www.twitter.com/",
"http://www.google.com/",
"http://www.cnn.com/" )
def timeMethod(method: () => Unit) = {
val start = System.nanoTime
method()
val end = System.nanoTime
println("Method took " + (end - start)/1000000000.0 + " seconds.")
}
def getPageSizeSequentially() = {
for(url <- urls) {
println("Size for " + url + ": " + PageLoader.getPageSize(url))
}
}
def getPageSizeConcurrently() = {
val caller = self
for(url <- urls) {
actor { caller ! (url, PageLoader.getPageSize(url)) }
}
for(i <- 1 to urls.size) {
receive {
case (url, size) =>
println("Size for " + url + ": " + size)
}
}
}
println("Sequential run:")
timeMethod { getPageSizeSequentially }
println("Concurrent run")
timeMethod { getPageSizeConcurrently }