====== Scala ======


**Sca**lable **la**nguage

===== Start =====


  * No primitive types, everything is an object
  * No semicolon
  * Object is a singleton
  * Methods can be defined private or protected. If no modifer is given, method is public.
  * No static methods


==== Hello World ====
<code scala>
object HelloWorld {
  def main(args: Array[String]) {
    println("Hello, world!")
  }
}
</code>

===== Control structures =====

if/else-Constructs have a return value

==== for loop ====
<code scala>
for (i <- 1 to 10) println(i)
</code>


<code scala>

// different steps
for (i <- 4 to (17,3)) println(i)
// other data types than int
for (s <- myList) println(s)

// multiple generators
for (i <- 0 to 2; j <- 3 to 4) println(i+" "+j)

// filter
    for {i <- 1 to 6         
         j <- 1 to 6
         if (i % 2 == 0)
         if (j % 2 != 0)} println(i+" "+j)
// yield
    val list: List[Int] = List(1,2,3,4)
    val result = for (i <- list) yield i * 2
    println(result)
</code>
==== match ====
Implizites break

<code scala>
val iValue = 3
iValue match{
  case 1 => println("one")
  case _ => println("empty")
}
</code>

===== Singleton objects =====

There are no static methods/vars in scala and singleton objects can't be constructed using a constructor with new.
<code scala>
object ScalaObject {

  val b = 5
  
  def test(a: Double) : Double = {
    3.* + b 
  }
}
</code>

===== Companion object =====

Prerequisite: object and class have the same name and are defined in the same file. Companion objects can access their private variables. Singleton objects without companion clases are standalone objects.

===== Case classes =====

  * Use a factory method for construction
  * All passed parameters are a val-variable of the class
  * Can be used for pattern matching
  * Implement toString, hashCode, equals and have a copy method

<code scala>
case class Person (firstName : String, lastName : String, age : Int){
  def isAdult : Boolean = if (age >= 18) true else false
}
</code>

===== Inheritance =====

Scala doesn't support multiple inheritance.

class B(arg:Int) extends A {}

Functions can be overridden with overide before func definition.

Overridding classes, functions or variables can be forbidden with prefix final.


==== Abstract classes ====

Difference to Traits: Abstract classes can have constructors. A class which inherits from an abstract class can't inherit from another.

The usage of override is optional.

==== Packages object ====

Objects which are visible in a whole package.



===== Identity and equality =====

==-Operator checks equality (identity in Java)
eq-Operator checks identity

eq and ne are only defined for clases of type scala.AnyRef.



===== Learning sources =====

http://www.scalatutorial.de/topic143.html