scala

Question

我有一个字符串变量需要解析为双精度

代码:

val myString = "9d"
myString.toDouble // produces "9.0" which i don't want. this should throws an error

如何使我的字符串按字面解释以产生异常？

Answer 1

我找到了 scalaz 的解决方案：

import scalaz.Scalaz._

println("34b".parseDouble) // Failure(java.lang.NumberFormatException: For input string: "34b")

println("34.4".parseDouble) // Success(34.4)

Answer 2

所以，显然，Java 的 java.lang.Double#parseDouble 能够解析各种字符串，例如NaN、Infinity 等

你的问题的答案似乎是BigDecimal(myString).toDouble

出于好奇，下面是针对各种输入字符串的三种不同方法 return：

  def main(args: Array[String]): Unit = {
    val strings = Seq("Infinity", "NaN", "9.0d", "9d", "9f", "9.0", "9.1", "1.4e14")
    val parsers = Seq(
      ("Double", (s: String) => s.toDouble),
      ("BigDecimal", (s: String) => BigDecimal(s).toDouble),
      ("NumberFormat", (s: String) => NumberFormat.getNumberInstance.parse(s).doubleValue()),
    )

    for (string <- strings) {
      println(s"\n------------- $string ------------")
      for ((name, parser) <- parsers) {
        val result = Try(parser(string)) match {
          case scala.util.Success(value) => value
          case scala.util.Failure(ex) => ex.toString
        }
        println(name.reverse.padTo(20, " ").reverse.mkString + " -> " + result)
      }

    }
  }

结果：

------------- Infinity ------------
              Double -> Infinity
          BigDecimal -> java.lang.NumberFormatException
        NumberFormat -> java.text.ParseException: Unparseable number: "Infinity"

------------- NaN ------------
              Double -> NaN
          BigDecimal -> java.lang.NumberFormatException
        NumberFormat -> java.text.ParseException: Unparseable number: "NaN"

------------- 9.0d ------------
              Double -> 9.0
          BigDecimal -> java.lang.NumberFormatException
        NumberFormat -> 9.0

------------- 9d ------------
              Double -> 9.0
          BigDecimal -> java.lang.NumberFormatException
        NumberFormat -> 9.0

------------- 9f ------------
              Double -> 9.0
          BigDecimal -> java.lang.NumberFormatException
        NumberFormat -> 9.0

------------- 9.0 ------------
              Double -> 9.0
          BigDecimal -> 9.0
        NumberFormat -> 9.0

------------- 9.1 ------------
              Double -> 9.1
          BigDecimal -> 9.1
        NumberFormat -> 9.1

------------- 1.4e14 ------------
              Double -> 1.4E14
          BigDecimal -> 1.4E14
        NumberFormat -> 1.4

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scala - restricted way of converting string to number

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