Beginning Scala 2nd Edition

1. Listing 3-10. Call by name
   
2. def nano() = {
   
3. println("Gettingnano")
   
4. System.nanoTime
   
5. }

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1. Listing 3-11. Call by name parameter
   
2. def delayed(t:=> Long) = {
   
3. println("Indelayed method")
   
4. println("Param:"+t)
   
5. t
   
6. }
   
7. Let’s see what happens when we call delayed with nano as a parameter:
   
8. scala> delayed(nano())
   
9. Indelayed method
   
10. Gettingnano
    
11. Param: 4475258994017
    
12. Gettingnano
    
13. res3:Long = 4475259694720

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1. Listing 3-12. Call by reference
   
2. def notDelayed(t:Long) = {
   
3. println("Innotdelayed method")
   
4. println("Param:"+t)
   
5. t
   
6. }
   
7. Let’s try calling notDelayed:
   
8. scala> notDelayed(nano())
   
9. Gettingnano
   
10. Innotdelayed method
    
11. Param: 4513758999378
    
12. res4:Long = 4513758999378

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1. Listing 3-13. Companion object
   
2. trait Shape {
   
3. def area :Double
   
4. }
   
5. object Shape {
   
6. private class Circle(radius: Double) extends Shape{
   
7. override val area = 3.14*radius*radius
   
8. }
   
9. private class Rectangle (height: Double, length: Double)extends Shape{
   
10. override val area = height * length
    
11. }
    
12. def apply(height :Double , length :Double ) : Shape = new Rectangle(height,length)
    
13. def apply(radius :Double) : Shape = new Circle(radius)
    
14. }

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1. Listing 3-14. Using import inside class body
   
2. classFrog {
   
3. importscala.xml._
   
4. defn:NodeSeq= NodeSeq.Empty
   
5. }

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1. Listing 3-15. Combining local scope import andimporting objects
   
2. scala> objectMoose{
   
3. defbark = "woof"
   
4. }
   
5. definedmodule Moose
   
6. scala> importMoose._
   
7. import Moose._
   
8. scala> bark

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1. Listing 3-16. Vehicle class
   
2. class Vehicle (speed : Int){
   
3. val mph :Int = speed
   
4. def race() = println("Racing")
   
5. }
   
6. The Vehicle class takes one argument, which is the speed of the vehicle. This argument must be passed
   
7. when creating an instance of class Vehicle, as follows: new Vehicle(100). The class contains one method,
   
8. called race.

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1. Listing 3-17. Overriding methods inherited from a super class
   
2. class Car (speed : Int) extends Vehicle(speed) {
   
3. override val mph: Int= speed
   
4. override def race() = println("Racing Car")
   
5. }
   
6. The class Car extends Vehicle class using the keyword extends. The field mph and the method race
   
7. needs to be overridden using the keyword override.
   
8. Listing 3-18 shows another class Bike that extends Vehicle.

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1. Listing 3-18. Vehicle hierarchy
   
2. class Vehicle (speed : Int){
   
3. val mph :Int = speed
   
4. def race() = println("Racing")
   
5. }
   
6. class Car (speed : Int) extends Vehicle(speed) {
   
7. override val mph: Int= speed
   
8. override def race() = println("Racing Car")
   
9. }
   
10. class Bike(speed : Int) extends Vehicle(speed) {
    
11. override val mph: Int = speed
    
12. override def race() = println("Racing Bike")
    
13. }

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1. Listing 3-20. Using with
   
2. class Batmobile(speed : Int) extends Vehicle(speed) with flying with gliding{
   
3. override val mph: Int = speed
   
4. override def race() = println("Racing Batmobile")
   
5. override def fly() = println("Flying Batmobile")
   
6. override def float() = println("Gliding Batmobile")
   
7. }
   
8. In Scala, traits can inherit classes. The keyword extends is also used when a class inherits a trait as its
   
9. parent. The keyword extends is also used even when the class mixes in other traits using the with keyword.
   
10. Also, extends is used when one trait is the child of another trait or class.
    
11. You can now create a Batmobile in the REPL as illustrated here:
    
12. scala> val vehicle3 = new Batmobile(300)
    
13. vehicle3: Batmobile = Batmobile@374ed5
    
14. Now

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