Introduction to Scala - Learn Java for Web Development - page 425

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")
}