Learn Java for Web Development

APPENDIX C: Introduction to Scala 429

Classes

Classes in Scala are declared very much like Java classes. One difference is that Scala classes can
have parameters, as illustrated in Listing C-10.

Listing C-10. Scala Class with Parameters

class Vehicle (speed : Int){
val mph :Int = speed
def race() = println("Racing")
}

The Vehicle class takes one argument, which is the speed of the vehicle. This argument must
be passed when creating an instance of class Vehicle, as follows: new Vehicle(100). The class
contains one method, called race().

Extending a Class

It is possible to override methods inherited from a superclass in Scala, as illustrated in Listing C-11.

Listing C-11. Extending a Scala Class

1. class Car (speed : Int) extends Vehicle(speed) {


2. override val mph: Int= speed


3. override def race() = println("Racing Car")


4. }

   Line 1: The Car class extends the Vehicle class using the keyword extends.

   Lines 2 to 3: The field mph and the method race() need to be overridden using

the keyword override.

Listing C-12 illustrates another class called Bike that extends Vehicle.

Listing C-12. Extending a Scala Class

class Vehicle (speed : Int){
val mph :Int = speed
def race() = println("Racing")
}
class Car (speed : Int) extends Vehicle(speed) {
override val mph: Int= speed
override def race() = println("Racing Car")

}
class Bike(speed : Int) extends Vehicle(speed) {
override val mph: Int = speed
override def race() = println("Racing Bike")

}