从“Scala第三版编程”第10章中获得StackOverFlowError

Question

我正在处理"scala第三版编程“第10章中的类元素和螺旋示例。现在我尝试使用”Scala螺旋8“运行它，并得到了错误：

线程"main“java.lang.StackOverflowError中的异常

 at java.base/java.lang.String.(String.java:250)

 at java.base/java.lang.String.valueOf(String.java:2802)

 at java.base/java.lang.Character.toString(Character.java:7563)

 at Element$UniformElement.(Element.scala:9)

 at Element$.elem(Element.scala:24)

 at Element.heighten(Element.scala:66)

 at Element.beside(Element.scala:46)

 at Element.widen(Element.scala:59)

等等..。

我对Scala还不熟悉，为了不感到沮丧和改进，所以如果您想清楚了，请尽可能地描述一下您是如何发现这个错误的，以及它是什么。谢谢!

下面是代码：

object Element {
  private class ArrayElement(val contents: Array[String]) extends Element

  private class UniformElement(
                                ch: Char,
                                override val height: Int,
                                override val width: Int
                              ) extends Element {
    private val line = ch.toString * width
    def contents: Array[String] = Array.fill(height)(line)
  }

  private class LineElement(s: String) extends Element {
    val contents = Array(s)
    override def width: Int = s.length
    override def height = 1
  }

  def elem(contents: Array[String]): Element = {
    new ArrayElement(contents)
  }

  def elem(ch: Char, height: Int, width: Int): Element = {
    new UniformElement(ch, height, width)
  }

  def elem(line: String): Element = {
    new LineElement(line)
  }
}

import Element.elem
abstract class Element {
  def contents: Array[String]

  def width: Int = contents(0).length
  def height: Int = contents.length

  def above(that: Element): Element = {
    val this1 = this widen that.width
    val that1 = that widen this.width
    elem(this1.contents ++ that1.contents)
  }

  def beside(that: Element): Element = {
    val this1 = this heighten that.height
    val that1 = that heighten this.height
    elem(
      for ((line1, line2) <- this1.contents zip that1.contents)
        yield line1 + line2
    )
  }

  def widen(w: Int): Element = {
    if (w <= width) this
    else {
      val left = elem(' ', (w - width) / 2, height)
      val right = elem(' ', w - width - left.width, height)
      left beside this beside right
    }
  }

  def heighten(h: Int): Element = {
    if (h <= height) this
    else {
      val top = elem(' ', width, (h - height) / 2)
      val bot = elem(' ', width, h - height - top.height)
      top above this above bot
    }
  }

  override def toString: String = contents mkString "\n"
}

import Element.elem
object Spiral {
  val space: Element = elem(" ")
  val corner: Element = elem("+")

  def spiral(nEdges: Int, direction: Int): Element = {
    if (nEdges == 1)
      elem("+")
    else {
      val sp = spiral(nEdges -1, (direction + 3) % 4)
      def verticalBar = elem('|', 1, sp.height)
      def horizontalBar = elem('-', sp.width, 1)
      if (direction == 0)
        (corner beside horizontalBar) above (sp beside space)
      else if (direction == 1)
        (sp above space) beside (corner above verticalBar)
      else if (direction == 2)
        (space beside sp) above (horizontalBar beside corner)
      else
        (verticalBar above corner) beside (space above sp)
    }
  }

  def main(args: Array[String]): Unit = {
    val nSides = args(0).toInt
    println(spiral(nSides, 0))
  }
}

Answer 1

您刚刚在width，elem中倒置了UniformElement和height参数的顺序。因此，当您从elem和widen调用heighten时，您传递了高度的宽度，反之亦然。