Scala Classes Examples

Classes.scala

object Classes {

  class MyFirstClass

  val myFirstClass = new MyFirstClass

  //---------------------------------------------//

  class Vehicle(
      var passengers: Int, //number of passengers
      var speed: Int,      //speed value
      val unit: String     //speed unit 
  ) {
    override def toString: String = s"(passengers: $passengers, speed: $speed $unit)"
  }

  val bicycle = new Vehicle(1, 30, "km")
  bicycle.passengers // 1
  bicycle.passengers = 2
  bicycle.passengers // 2
  println(bicycle)   // (passengers: 2, speed: 30 km)

  //---------------------------------------------//

  class Vehicle1(
      var passengers: Int,
      private val speed: Int,
      private val unit: String = "km"
  ) {
    val speedDescription: String  = s"$speed $unit"
    override def toString: String = s"(passengers: $passengers, speed: $speedDescription)"
  }

  object Vehicle1 {
    def speed220km(passengers: Int): Vehicle1 = new Vehicle1(passengers, 220, "km")
  }

  val motorcycle = new Vehicle1(2, 100)
  motorcycle.passengers       // 2
  motorcycle.speed            // don't compile because the attribute is private
  motorcycle.speedDescription // 100 km
  println(motorcycle)         // (passengers: 2, speed: 100 km)

  val car: Vehicle1 = Vehicle1.speed220km(5)
  println(car) // (passengers: 5, speed: 220 km)

  //---------------------------------------------//

  case class Vehicle2(passengers: Int, speed: Int, unit: String) {
    val speedDescription: String = s"$speed $unit"
  }

  // Normal constructor and the most used
  val myCar  = Vehicle2(5, 200, "km")
  // Using apply explicitly
  val myCar1 = Vehicle2.apply(5, 200, "km")
  // By "tuple" of values
  val myCar2 = Vehicle2.tupled((5, 200, "km"))
  // Through currying mode parameters
  val myCar3 = Vehicle2.curried(5)(200)("km")

  // use the automatically generated methods
  myCar.passengers     // 5
  myCar.speed          // 200
  myCar.speed = 300    // don't compile -> error: reassignment to val
  myCar.unit           // km
  println(myCar)       // Vehicle2(5,200,km)

  val myFastCar = myCar.copy(passengers = 2, speed = 320)
  println(myFastCar) // Vehicle2(2,320,km)

  // compare by structure and not by reference
  myCar == myCar1    // true
  myCar == myCar2    // true
  myCar == myCar3    // true
  myCar == myFastCar // false


  // use the unapply in match expressions
  def recognizeVehicle(x: Vehicle2): String = x match {
  case Vehicle2(10, speed, unit) =>
    s"10 passenger minivan with speed of $speed $unit"
  case Vehicle2(2, speed, _) if speed > 300 =>
    s"High speed sports car ${x.speedDescription}"
  case _ =>
    "Any non-minivan or sports car: " + x
  }

  val minivan = Vehicle2(10, 100, "km")
  println(recognizeVehicle(minivan))
  // 10 passenger minivan with speed of 100 km

  println(recognizeVehicle(myFastCar))
  // High speed sports car 320 km

  println(recognizeVehicle(myCar))
  // Any non-minivan or sports car: Vehicle2(5,200,km)

  //--------------------------------------------------//

  sealed trait Animal {
  def name: String
  }

  case class Dog(name: String, owner: String) extends Animal
  case class Cat(name: String, color: String) extends Animal

  def recognizeAnimal(a: Animal): String = a match {
    case Dog(name, owner) => s"The dog $name belongs to $owner."
    case Cat(name, color) => s"${name.capitalize} is a very beautiful $color cat."
  }

  val bony = Dog("Bony", "Pedrito")
  val tom  = Cat("tom", "negro")

  println(recognizeAnimal(bony))
  // The dog Bony belongs to Pedrito.

  println(recognizeAnimal(tom))
  // Tom is a very beautiful black cat.