Classes.scala

object Trond {
  val age = 25 // value - immutable variable - final in java
  def sayHi = println(s"My name is Trond and I'm $age years old!") // definition - method 
}

// Trond.age = 27 does not compile as age is immutable (val)
Trond.sayHi

object Eli { // singleton object - only one of these in the JVM
  var age = 22 // variable (mutable) 
  def sayHi = println(s"My name is Eli and I'm $age years old!") 
}

Eli.age = 27 // compiles as age is mutable (var)

class Person(val name: String, val age: Int) { // adding the val will promote the class parameter to a field
  def sayHi = println(s"My name is $name and I'm $age years old!") // string interpolation - use $ or ${} to access variables
}

val elisabeth = new Person("Elisabeth", 22) // the type is infered by the compiler 
val trond : Person = new Person("Trond", 25) // we can also explicitly specify the type

// Let's make everyone say hi
def introduceAll(persons: List[Person]) = {
  for (p <- persons) p.sayHi
}

introduceAll(List(elisabeth, trond))

// a tiny bit of inheritance 
class Organiser(name: String, age: Int, task: String) extends Person(name, age) {
  override def sayHi = println(s"My name is $name ($age) and today I will $task.") // we specialise the sayHi for the Organiser
}

introduceAll(List(elisabeth, trond, new Organiser("Antoine", 24, "present Spray")))