Scala example source code file (iterators.scala)

This example Scala source code file (iterators.scala) is included in the DevDaily.com "Java Source Code Warehouse" project. The intent of this project is to help you "Learn Java by Example" ^TM.

Java - Scala tags/keywords

a, a, array, int, int, list, list, string, string, test, throwable

The Scala iterators.scala source code

//############################################################################
// Iterators
//############################################################################

//############################################################################

object Test {

  def check_from: Int = {
    val it1 = Iterator.from(-1)
    val it2 = Iterator.from(0, -1)
    it1.next + it2.next
  }

  def check_range: Int = {
    val xs1 = Iterator.range(0, 10,  2) toList;
    val xs2 = Iterator.range(0, 10, -2) toList;
    val xs3 = Iterator.range(10, 0, -2) toList;
    val xs4 = Iterator.range(10, 0,  2) toList;
    val xs5 = Iterator.range(0, 10, 11) toList;
    xs1.length + xs2.length + xs3.length + xs4.length + xs5.length
  }

  def check_range2: Int = {
    val r1start = 0
    val r1end = 10
    val r1step = 1
    val r1 = Iterator.range(r1start, r1end, r1step) toList;
    val r2 = Iterator.range(r1start, r1end, r1step + 1) toList;
    val r3 = Iterator.range(r1end, r1start, -r1step) toList;
    val r4 = Iterator.range(0, 10, 11) toList;
    // 10 + 5 + 10 + 1
    r1.length + r2.length + r3.length + r4.length
  }

  def check_range3: Int = {
    def trues(xs: List[Boolean]) = xs.foldLeft(0)((a, b) => if (b) a+1 else a)
    val r1 = Iterator.range(0, 10)
    val xs1 = List(r1 contains 5, r1 contains 6)
    val r2a = Iterator.range(0, 10, 2)
    val r2b = Iterator.range(0, 10, 2)
    val xs2 = List(r2a contains 5, r2b contains 6)
    val r3 = Iterator.range(0, 10, 11)
    val xs3 = List(r3 contains 5, r3 contains 6)
    // 2 + 1 + 0
    trues(xs1) + trues(xs2) + trues(xs3)
  }

  def check_take: Int = {
    val it1 = Iterator.from(0)
    val xs1 = it1 take 10 toList;
    xs1.length
  }

  def check_drop: Int = {
    val it1 = Iterator.from(0)
    val it2 = it1 map { 2 * _ }
    val n1 = it1 drop 2 next
    val n2 = it2 drop 2 next;
    n1 + n2
  }

  def check_foreach: Int = {
    val it1 = Iterator.from(0) take 20
    var n = 0
    it1 foreach { n += _ }
    n
  }

  def check_forall: Int = {
    val it1 = Iterator.from(0)
    val it2 = Iterator.from(1)
    0
  }

  def check_fromArray: Int = {  // ticket #429
    val a = List(1, 2, 3, 4).toArray
    var xs0 = Iterator.fromArray(a).toList;
    var xs1 = Iterator.fromArray(a, 0, 1).toList;
    var xs2 = Iterator.fromArray(a, 0, 2).toList;
    var xs3 = Iterator.fromArray(a, 0, 3).toList;
    var xs4 = Iterator.fromArray(a, 0, 4).toList;
    xs0.length + xs1.length + xs2.length + xs3.length + xs4.length
  }
  
  def check_toSeq: String =
    List(1, 2, 3, 4, 5).iterator.toSeq.mkString("x")
  
  def check_indexOf: String = {
    val i = List(1, 2, 3, 4, 5).indexOf(4)
    val j = List(1, 2, 3, 4, 5).indexOf(16)
    "" + i + "x" + j
  }
  
  def check_findIndexOf: String = {
    val i = List(1, 2, 3, 4, 5).indexWhere { x: Int => x >= 4 }
    val j = List(1, 2, 3, 4, 5).indexWhere { x: Int => x >= 16 }
    "" + i + "x" + j
  }

  def check_success[A](name: String, closure: => A, expected: A) {
    print("test " + name)
    try {
      val actual: A = closure
      if (actual == expected)
        print(" was successful")
      else
        print(" failed: expected "+ expected +", found "+ actual)
    }
    catch {
      case exception: Throwable =>
        print(" raised exception " + exception)
    }
    println()
  }

  def main(args: Array[String]) {
    check_success("check_from",     check_from,      -1)
    check_success("check_range",    check_range,     11)
    check_success("check_range2",   check_range2,    26)
    check_success("check_range3",   check_range3,     3)
    check_success("check_take",     check_take,      10)
    check_success("check_drop",     check_drop,      12)
    check_success("check_foreach",  check_foreach,  190)
    check_success("check_forall",   check_forall,     0)
    check_success("check_fromArray",check_fromArray, 14)
    check_success("check_toSeq",  check_toSeq, "1x2x3x4x5")
    check_success("check_indexOf",     check_indexOf,     "3x-1")
    check_success("check_findIndexOf", check_findIndexOf, "3x-1")
    println()
  }
}

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