SDC - Einführung in Scala

Einführung in Scala SDC 2011 - Seitenbau Konstanz Christian Baranowski Dennis Braunsdorf

Scala Bazaar Scala = Bazaar Java = Cathedral “ The Cathedral and the Bazaar” - Eric S. Raymond

Variablen var msg = "Hello SDC!" // Java Code String msg = "Hello World" ; val msg = "Hello SDC!“ // Java Code final String msg = "Hello World" ;

Funktionen def max(x : Int, y : Int) : Int = { if (x > y) { return x; } else { return y; } }

Funktionen def max(x : Int, y : Int) : Int = { if (x > y) { x } else { y } }

Funktionen def max(x : Int, y : Int) : Int = { if (x > y) x else y }

Funktionen def max(x : Int, y : Int) = { if (x > y) x else y }

Procedure def printer(msg : String) { ... }

Funktionen Composition and Scoping def max(x : Int, y : Int) = { def xGreater() = { x > y } if (xGreater()) x else y }

Funktionen Composition and Scoping def max(x : Int, y : Int) = { def xGreater() = { x > y } if (xGreater) x else y }

Functions are objects def oncePerSecond(callback: () => Unit) { while ( true ) { callback(); Thread sleep 1000 } } def timeFlies() { println( "time flies like an arrow..." ) } oncePerSecond(timeFlies)

Anonymous Functions def oncePerSecond(callback: () => Unit) { while ( true ) { callback(); Thread sleep 1000 } } oncePerSecond(() => println( "time flies like an arrow..." ))

Arrays val names = new Array[String](2) names(0) = "Dennis" names(1) = "Christian"

Arrays val names = Array( "Dennis" , "Christian" )

Arrays val names = Array( "Dennis" , "Christian" , true , 0, 1.5) val names : Array[Any] = Array( "Dennis" , "Christian" , true , 0, 1.5)

Listen val oneTwo = List(1, 2) val threeFour = List(3, 4) val oneTwoThreeFour = oneTwo ::: threeFour val oneTwoThree = 1 :: 2 :: 3 :: Nil

Tuples val dennis = (1, "Dennis" ) val christian = (2, "Christian" ) val dennis = ( "Dennis" , "Braunsdorf" ) println(dennis._1) println(dennis._2)

Sets import scala.collection.mutable.HashSet val jetSet = new HashSet[String] jetSet += "Lear" jetSet += ( "Boeing" , "Airbus" ) println(jetSet.contains( "Cessna" ))

Sets val jetSet = Set( "AirBus" ) jetSet: scala.collection.immutable.Set[java.lang.String]

Maps import scala.collection.mutable.HashMap val treasureMap = new HashMap[Int, String] treasureMap += 1 -> "Go to island." treasureMap += 2 -> "Find big X on ground." treasureMap += 3 -> "Dig." println(treasureMap(2))

Maps val treasureMap = Map( (1, "Go to island." ), (2, "Find big X on ground." ), (3, "Dig." ) )

While Schleife val names = Array( "Dennis" , "Christian" ) var i = 0 while (i < names.length) { println(names(i)) i = i + 1 }

For Schleife val names = Array( "Dennis" , "Christian" ) for (name <- names) println(name)

Foreach Collection val names = Array( "Dennis" , "Christian" ) names.foreach(name => println(name))

Throw Exceptions def max(x : Int, y : Int) : Int = { if (x < 0) throw new Exception( "Negativ Int!" ) ... }

Catch Exceptions try { ... } catch { case ioe: IOException => println( "Fehler beim lesen auf dem Filesystem" ) case e: Exception => println( "Unbekannter Fehler" ) }

Numbers are Objects 1 + 2 * 3 / x = (1).+(((2).*(3))./(x))

Objekte object DemoService { def print(msg : String) { println(msg) } } DemoService.print( "Hello World" )

Klassen class Complex(real: Double, imaginary: Double) { def re() = real def im() = imaginary }

Klassen class Complex(real: Double, imaginary: Double) { def re = real def im = imaginary }

Abstrakte Klassen abstract class Complex(real: Double, imaginary: Double) { abstract def re() def im = imaginary }

Klassen protected class Complex(real: Double, imaginary: Double) { private def re() = real protected def im() = imaginary }

Auxiliary Constructors class Complex(real: Double, imaginary: Double) { def this () = this (0,0) def re() = real def im() = imaginary }

Packages und Imports package demo import javax._ import scala.collection.mutable.HashMap

Scala Live Demo Getting Started ….

Traits trait Ord { def < (that: Any): Boolean def <=(that: Any): Boolean = ( this < that) || ( this == that) def > (that: Any): Boolean = !( this <= that) def >=(that: Any): Boolean = !( this < that) } trait Service class MyOrd extends Ord with Service { def < (that: Any): Boolean = false }

Operators + * - / class Demo { def + (x : Int) = 1 + x } var o1 = new MyOrd println(o1 + 1)

Methoden Overloading class Demo { def + (x : Int) = 1 + x def + (x : Demo) = 1 + 1 }

Methoden Überschreiben class Complex(real: Double, imaginary: Double) { def re = real def im = imaginary override def toString() = "" + re + ( if (im < 0) "" else "+" ) + im + "i„ }

Case Klassen abstract class Tree case class Sum(l: Tree, r: Tree) extends Tree case class Var(n: String) extends Tree case class Const(v: Int) extends Tree

Pattern Matching def eval(t: Tree, env: Environment): Int = t match { case Sum(l, r) => eval(l, env) + eval(r, env) case Var(n) => env(n) case Const(v) => v } def derive(t: Tree, v: String): Tree = t match { case Sum(l, r) => Sum(derive(l, v), derive(r, v)) case Var(n) if (v == n) => Const(1) case _ => Const(0) } val exp: Tree = Sum(Sum(Var( "x" ),Var( "x" )),Sum(Const(7),Var( "y" ))) val env: Environment = { case "x" => 5 case "y" => 7 } println( "Expression: " + exp) println( "Evaluation with x=5, y=7: " + eval(exp, env)) println( "Derivative relative to x:\n " + derive(exp, "x" )) println( "Derivative relative to y:\n " + derive(exp, "y" ))

For-Comprehensions for (p <- persons if p.age > 20) yield p.name def queens(n: Int): List[List[Int]] = { def placeQueens(k: Int): List[List[Int]] = if (k == 0) List(List()) else for { queens <- placeQueens(k - 1) column <- List.range(1, n + 1) if isSafe(column, queens, 1) } yield column :: queens placeQueens(n) } def isSafe(col: Int, queens: List[Int], delta: Int): Boolean for (b <- books; a <- b.authors if a startsWith "Ullman" ) yield b.title

Genericity class Reference[T] { private var contents: T = _ def set(value: T) { contents = value } def get: T = contents } object IntegerReference { def main(args: Array[String]) { val cell = new Reference[Int] cell.set(13) println( "Reference contains the half of " + (cell.get * 2)) } }

Generic Stack abstract class Stack[A] { def push(x: A): Stack[A] = new NonEmptyStack[A](x, this ) def isEmpty: Boolean def top: A def pop: Stack[A] } class EmptyStack[A] extends Stack[A] { def isEmpty = true def top = error( "EmptyStack.top" ) def pop = error( "EmptyStack.pop" ) } class NonEmptyStack[A](elem: A, rest: Stack[A]) extends Stack[A] { def isEmpty = false def top = elem def pop = rest }

Lazy Values case class Employee(id: Int, name: String, managerId: Int) { lazy val manager: Employee = Db.get(managerId) lazy val team: List[Employee] = Db.team(id) }

Implicit Parameters implicit object stringMonoid extends Monoid[String] { def add(x: String, y: String): String = x.concat(y) def unit: String = "" } implicit object intMonoid extends Monoid[Int] { def add(x: Int, y: Int): Int = x + y def unit: Int = 0 }

Implicit Conversions implicit def int2ordered(x: Int): Ordered[Int] = new Ordered[Int] { def compare(y: Int): Int = if (x < y) -1 else if (x > y) 1 else 0 }

Annotations @field class BeanProperty extends annotation.StaticAnnotation

Scala Java Integration // Java public class MainJava { public static void main(String[] args) { Point point = new Point(); point.name(); } } // Scala class Point(x : Int, y : Int) { var name = "Bin ein Point" def this () = this (0, 0) override def toString = name + " : x=" + x + " : y=" + y }

Package Objects package object demo { implicit def toPoint(name: String) = new Point }

Java Beans mit Scala class PersonBean { @scala.reflect.BeanProperty var name : String = "" }

JUnit Tests with Scala import org.junit._ import org.junit.Assert._; class MaxTest { var max : MathUtils = null ; @Before def setup(){ max = new MathUtils } @Test def max_fiveGreaterThenFour() { assertEquals(5, max.max(5, 4)); } }

Robot DSL object DemoRobot extends RobotProgram with Application { 000 PRINT "Lunar Mars Program starts." 001 MOVE(1, 10) 002 SLEEP2000 003 MOVE(10, 10) 004 PRINT "POSITION Now 10, 10" 005 MOVE(20, 20) 006 END RUN }

References Scala – http://www.scala-lang.org/ Scala IDE - http://www.scala-ide.org/ Scala Code Snippets http://www.scala-lang.org/node/220 Scala By Example http://www.scala-lang.org/docu/files/ScalaByExample.pdf Scala Tutorial http://www.scala-lang.org/docu/files/ScalaTutorial.pdf Scala Actors - http://www.scala-lang.org/node/242 Lift http://liftweb.net

SDC - Einführung in Scala

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