Return to chapter index

3 Next Steps in Scala

// In file next-steps-in-scala/Ex1.scala

  val big = new java.math.BigInteger("12345")


// In file next-steps-in-scala/Ex1.scala

  val greetStrings = new Array[String](3)
  
  greetStrings(0) = "Hello"
  greetStrings(1) = ", "
  greetStrings(2) = "world!\n"

  for (i <- 0 to 2)
    print(greetStrings(i))


// In file next-steps-in-scala/Ex2.scala

  val greetStrings: Array[String] = new Array[String](3)


// In file next-steps-in-scala/Ex2.scala

  greetStrings(0) = "Hello"
  greetStrings(1) = ", "
  greetStrings(2) = "world!\n"


// In file next-steps-in-scala/Ex2.scala

  for (i <- 0 to 2)
    print(greetStrings(i))


  greetStrings(0) = "Hello" 


  greetStrings.update(0, "Hello")


// In file next-steps-in-scala/Ex3.scala

  val greetStrings = new Array[String](3)

  greetStrings.update(0, "Hello")
  greetStrings.update(1, ", ")
  greetStrings.update(2, "world!\n")

  for (i <- 0.to(2))
    print(greetStrings.apply(i))


// In file next-steps-in-scala/Ex3.scala

  val numNames = Array("zero", "one", "two")


// In file next-steps-in-scala/Ex3.scala

  val numNames2 = Array.apply("zero", "one", "two")


  

Step 1. Use lists

// In file next-steps-in-scala/Ex3.scala

  val oneTwoThree = List(1, 2, 3)


// In file next-steps-in-scala/Ex3.scala

  val oneTwo = List(1, 2)
  val threeFour = List(3, 4)
  val oneTwoThreeFour = oneTwo ::: threeFour
  println(oneTwo + " and " + threeFour + " were not mutated.")
  println("Thus, " + oneTwoThreeFour + " is a new list.")


  List(1, 2) and List(3, 4) were not mutated.
  Thus, List(1, 2, 3, 4) is a new list.


// In file next-steps-in-scala/Ex3.scala

  val twoThree = List(2, 3)
  val oneTwoThree = 1 :: twoThree
  println(oneTwoThree)


  List(1, 2, 3)


// In file next-steps-in-scala/Ex3.scala

  val oneTwoThree = 1 :: 2 :: 3 :: Nil
  println(oneTwoThree)


  

Step 2. Use tuples

// In file next-steps-in-scala/Ex3.scala

  val pair = (99, "Luftballons")
  println(pair._1)
  println(pair._2)


  99
  Luftballons


  

Step 3. Use sets and maps

// In file next-steps-in-scala/Ex3.scala

  var jetSet = Set("Boeing", "Airbus")
  jetSet += "Lear"
  println(jetSet.contains("Cessna"))


// In file next-steps-in-scala/Ex3.scala

  jetSet = jetSet + "Lear"


// In file next-steps-in-scala/Ex3.scala

  import scala.collection.mutable

  val movieSet = mutable.Set("Hitch", "Poltergeist")
  movieSet += "Shrek"
  println(movieSet) 


// In file next-steps-in-scala/Ex3.scala

  import scala.collection.immutable.HashSet

  val hashSet = HashSet("Tomatoes", "Chilies")
  println(hashSet + "Coriander")


// In file next-steps-in-scala/Ex3.scala

  import scala.collection.mutable

  val treasureMap = mutable.Map[Int, String]()
  treasureMap += (1 -> "Go to island.")
  treasureMap += (2 -> "Find big X on ground.")
  treasureMap += (3 -> "Dig.")
  println(treasureMap(2))


  Find big X on ground.


// In file next-steps-in-scala/Ex3.scala

  val romanNumeral = Map(
    1 -> "I", 2 -> "II", 3 -> "III", 4 -> "IV", 5 -> "V"
  )
  println(romanNumeral(4))


  

Step 4. Learn to recognize the functional style

// In file next-steps-in-scala/Ex3.scala

  def printArgs(args: Array[String]): Unit = {
    var i = 0
    while (i < args.length) {
      println(args(i))
      i += 1
    }
  }


// In file next-steps-in-scala/Ex3.scala

  def printArgs(args: Array[String]): Unit = {
    for (arg <- args)
      println(arg)
  }


// In file next-steps-in-scala/Ex3.scala

  def printArgs(args: Array[String]): Unit = {
    args.foreach(println)
  }


// In file next-steps-in-scala/Ex3.scala

  def formatArgs(args: Array[String]) = args.mkString("\n")


// In file next-steps-in-scala/Ex3.scala

  println(formatArgs(args))


// In file next-steps-in-scala/Ex3.scala

  val res = formatArgs(Array("zero", "one", "two"))
  assert(res == "zero\none\ntwo")


  

Step 5. Read lines from a file

// In file next-steps-in-scala/countchars1.scala

  import scala.io.Source

  if (args.length > 0) {

    for (line <- Source.fromFile(args(0)).getLines())
      println(line.length + " " + line)
  }
  else
    Console.err.println("Please enter filename")


  $ scala countchars1.scala countchars1.scala


  22 import scala.io.Source
  0 
  22 if (args.length > 0) {
  0 
  51   for (line <- Source.fromFile(args(0)).getLines())
  37     println(line.length + " " + line)
  1 }
  4 else
  46   Console.err.println("Please enter filename")


  22 | import scala.io.Source
   0 | 
  22 | if (args.length > 0) {
   0 | 
  51 |   for (line <- Source.fromFile(args(0)).getLines())
  37 |     println(line.length + " " + line)
   1 | }
   4 | else
  46 |   Console.err.println("Please enter filename")


// In file next-steps-in-scala/Ex4.scala

  val lines = Source.fromFile(args(0)).getLines().toList


// In file next-steps-in-scala/Ex4.scala

  def widthOfLength(s: String) = s.length.toString.length


// In file next-steps-in-scala/Ex4.scala

  var maxWidth = 0
  for (line <- lines)
    maxWidth = maxWidth.max(widthOfLength(line))


// In file next-steps-in-scala/Ex5.scala

  val longestLine = lines.reduceLeft(
    (a, b) => if (a.length > b.length) a else b 
  ) 


// In file next-steps-in-scala/Ex5.scala

  val maxWidth = widthOfLength(longestLine)


// In file next-steps-in-scala/Ex5.scala

  for (line <- lines) {
    val numSpaces = maxWidth - widthOfLength(line)
    val padding = " " * numSpaces
    println(padding + line.length + " | " + line)
  }


// In file next-steps-in-scala/Ex6.scala

  import scala.io.Source

  def widthOfLength(s: String) = s.length.toString.length

  if (args.length > 0) {

    val lines = Source.fromFile(args(0)).getLines().toList

    val longestLine = lines.reduceLeft(
      (a, b) => if (a.length > b.length) a else b 
    ) 
    val maxWidth = widthOfLength(longestLine)

    for (line <- lines) {
      val numSpaces = maxWidth - widthOfLength(line)
      val padding = " " * numSpaces
      println(padding + line.length + " | " + line)
    }
  }
  else
    Console.err.println("Please enter filename")