Scala
Meine Scala Notizen
Contents
Konsolentools
scala Konsole
scala Konsole aufstarten:
scala
scala compiler
Scala Compiler:
scalac WorldlyApp.scala WorldlyGreeter.scala
Scala Compiler Daemon:
fsc WorldlyApp.scala WorldlyGreeter.scala
Ausführen kann man Programme wie folgt:
scala classpath . HelloWorld
var und val
Wichtige Keywords:
- var: Variable, wie ref.
- val: Value, nicht mutierbar.
Methoden
Methode definieren:
scala> def max(x: Int, y: Int): Int = if (x < y) y else x
max: (Int,Int)Int
scala> max(4,55)
res5: Int = 55
scala>
singletons
WorldlyGreeter ist als Klasse und Object definiert. worldify ist statisch (im Bytecode).
// The WorldlyGreeter class
class WorldlyGreeter(greeting: String) {
def greet() = {
val worldlyGreeting = WorldlyGreeter.worldify(greeting)
println(worldlyGreeting)
}
}
// The WorldlyGreeter companion object
object WorldlyGreeter {
def worldify(s: String) = s + ", world!"
}
var x = new WorldlyGreeter("Hello testmaster.ch") x.greet()
imports
- _: Ist analog zu Javas *
- {Date, Locale}: Mehrere Klassen werden auf einer Zeile importiert.
import java.util.{Date, Locale}
import java.text.DateFormat
import java.text.DateFormat._
object FrenchDate {
def main(args: Array[String]) {
val now = new Date
val df = getDateInstance(LONG, Locale.FRANCE)
println(df format now)
}
}
Closures, Delegates
Uint ist wie void.
object Timer {
def oncePerSecond(callback: () => Unit) {
while (true) { callback(); Thread sleep 1000 }
}
def timeFlies() {
println("time flies like an arrow...")
}
def main(args: Array[String]) {
oncePerSecond(timeFlies)
}
}
Anonyme Methoden:
object TimerAnonymous {
def oncePerSecond(callback: () => Unit) {
while (true) { callback(); Thread sleep 1000 }
}
def main(args: Array[String]) {
oncePerSecond(() =>
println("time flies like an arrow..."))
}
}
traits, mixins
simple
trait Friendly {
def greet() = "Hi"
}
class Dog extends Friendly {
override def greet() = "Woof"
}
class HungryCat extends Friendly {
override def greet() = "Meow"
}
class HungryDog extends Dog {
override def greet() = "I'd like to eat my own dog food"
}
trait ExclamatoryGreeter extends Friendly {
override def greet() = super.greet() + "!"
}
var pet: Friendly = new Dog
println(pet.greet())
pet = new HungryCat
println(pet.greet())
pet = new HungryDog
println(pet.greet())
pet = new Dog with ExclamatoryGreeter
println(pet.greet())
pet = new HungryCat with ExclamatoryGreeter
println(pet.greet())
pet = new HungryDog with ExclamatoryGreeter
println(pet.greet())
Mixin mit Nutzen
Demonstriert Mixins. Das Mixin Ord enthält Implementationen und Deklarationen. Eine Klasse, welches das Mixin implementiert, muss nur eine Methode implementieren und hat die anderen gratis.
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)
}
class Person extends Ord {
var age = 0
def < (that: Any): Boolean = {
var p: Person = that.asInstanceOf[Person];
if(p.age > this.age)
true
else
false
}
}
var simone: Person = new Person
var steff: Person = new Person
simone.age = 17
steff.age = 16
println(simone > steff)
println(steff >= simone)
