Foundations

Collections

Collections keep related values together and let code read values by index.

array index Array indexes start at zero, so `scores(0)` reads the first value.

Collections

bonus
Collections.scala
Replay: real traced execution (multi-file project)
object Main {
  def main(args: Array[String]): Unit = {
    val scores = Array(82, 91, 76)
    val bonus = 5
    val firstScore = scores(0)
    val adjustedScore = scores(1) + bonus

    println("first=" + firstScore)
    println("adjusted=" + adjustedScore)
  }
}

object Main {
  def main(args: Array[String]): Unit = {
    val scores = Array(82, 91, 76)
    val bonus = 0
    val firstScore = scores(0)
    val adjustedScore = scores(1) + bonus

    println("first=" + firstScore)
    println("adjusted=" + adjustedScore)
  }
}

object Main {
  def main(args: Array[String]): Unit = {
    val scores = Array(82, 91, 76)
    val bonus = 10
    val firstScore = scores(0)
    val adjustedScore = scores(1) + bonus

    println("first=" + firstScore)
    println("adjusted=" + adjustedScore)
  }
}

  1. bonus ← 5, firstScore ← 82, adjustedScore ← 96

    1object Main {2  def main(args: Array[String]): Unit = {3    val scores = Array(82, 91, 76)4    val bonus→ 5 = 5 //@bonus=0, 105    val firstScore→ 82 = scores(0)826    val adjustedScore→ 96 = scores(1)91 + bonus578    println("first=" + firstScore82)9    println("adjusted=" + adjustedScore96)10  }11}
    outputfirst=82
adjusted=96

  1. bonus ← 0, firstScore ← 82, adjustedScore ← 91

    1object Main {2  def main(args: Array[String]): Unit = {3    val scores = Array(82, 91, 76)4    val bonus→ 0 = 05    val firstScore→ 82 = scores(0)826    val adjustedScore→ 91 = scores(1)91 + bonus078    println("first=" + firstScore82)9    println("adjusted=" + adjustedScore91)10  }11}
    outputfirst=82
adjusted=91

  1. bonus ← 10, firstScore ← 82, adjustedScore ← 101

    1object Main {2  def main(args: Array[String]): Unit = {3    val scores = Array(82, 91, 76)4    val bonus→ 10 = 105    val firstScore→ 82 = scores(0)826    val adjustedScore→ 101 = scores(1)91 + bonus1078    println("first=" + firstScore82)9    println("adjusted=" + adjustedScore101)10  }11}
    outputfirst=82
adjusted=101

What Happens

  1. scores starts as 82, 91, and 76.
  2. bonus starts at 5.
  3. scores(0) reads 82.
  4. scores(1) + bonus adds 91 + 5.
  5. The program prints first=82 and adjusted=96.

Collection Picture

| bonus | first value | adjusted value | | --- | --- | --- | | 0 | 82 | 91 | | 5 | 82 | 96 | | 10 | 82 | 101 |

Exercise: Collections.scala

Reproduce first=82 and adjusted=96, then use the pinned bonuses 0 and 10 to predict each adjusted value.