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Scala for the Impatient: Chapter 6 exercises solutions
//1. Write an object Conversions with methods inchesToCentimeters, gallonsToLiters, and
//milesToKilometers.
object Conversions {
def inchesToCentimeters(inches: Double) = inches * 2.54
def gallonsToLiters(gallons: Double) = gallons * 3.78541
def milesToKilometers(miles: Double) = miles * 1.60934
}
//2. The preceding problem wasn't very object-oriented. Provide a general superclass
//UnitConversion and define objects InchesToCentimeters, GallonsToLiters, and
//MilesToKilometers that extend it.
class UnitConversion(val conversionFactor: Double) {
private def convert(value: Double) = value * conversionFactor
def apply(value: Double) = convert(value)
}
object InchesToCentimeters extends UnitConversion(2.54) {}
object GallonsToLiters extends UnitConversion(3.78541) {}
object MilesToKilometers extends UnitConversion(1.60934) {}
//3. Define an Origin object that extends java.awt.Point. Why is this not actually a
//good idea? (Have a close look at the methods of the Point class.)
// Maybe because Point class has a move() etc. methods and origin shouldn't move??
object Origin extends java.awt.Point {}
//4. Define a Point class with a companion object so that you can construct Point
//instances as Point(3, 4), without using new.
class Point(val x: Int, val y: Int) {
override def toString = "(" + x + ", " + y + ")"
}
object Point {
def apply(x: Int, y: Int) = new Point(x, y)
}
//5. Write a Scala application, using the App trait, that prints the command-line
//arguments in reverse order, separated by spaces. For example, scala Reverse
//Hello World should print World Hello.
object Reverse extends App {
for(s <- args.reverse) print(s + " ")
println()
}
//6. Write an enumeration describing the four playing card suits so that the toString
//method returns ♣, ♦, ♥, or ♠.
object CardSuite extends Enumeration {
type CardSuite = Value
val Club = Value("")
val Diamond = Value("")
val Heart = Value("")
val Spade = Value("")
}
//7. Implement a function that checks whether a card suit value from the preceding exercise is red.
import CardSuite._
def isRed(card: CardSuite) = card == Diamond || card == Heart
//8. Write an enumeration describing the eight corners of the RGB color cube. As
//IDs, use the color values (for example, 0xff0000 for Red).
object RGBCube extends Enumeration {
val Black = Value(0x000000, "Black")
val Red = Value(0xff0000, "Red")
val Green = Value(0x00ff00, "Green")
val Yellow = Value(0xffff00, "Yellow")
val Blue = Value(0x0000ff, "Blue")
val Cyan = Value(0x00ffff, "Cyan")
val Magenta = Value(0xff00ff, "Magenta")
val White = Value(0xffffff, "White")
}
@jg123

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@jg123 jg123 commented Jun 28, 2015

For answer 7, Spade should be Heart.

@sinedsem

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@sinedsem sinedsem commented Jun 16, 2016

My 6:

object Reverse extends App {
  print(args.reverse.mkString(" "))
}
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