Scala - Core Scala - Functions(Converting, Strong to Double(toDouble method))

Learning Scala:
Practical Functional Programming for the JVM
(O'Reilly Media)
Jason Swartz (著)

開発環境

• OS X Yosemite - Apple (OS)
• Emacs (Text Editor)
• Scala (プログラミング言語)

Learning Scala: Practical Functional Programming for the JVM (Jason Swartz (著)、O'Reilly Media)のPart Ⅰ. (Core Scala)、Chapter 4.(Functions)、Exercises 2.(No. 1471)を解いてみる。

その他参考書籍

• Programming Scala: Scalability = Functional Programming + Objects

Exercises 2.(No. 1471)

コード(Emacs)

def areaOrCircle(radius: String): Double = {
  val r = radius.toDouble
  r * r * 3.14
}

println(areaOrCircle("1"))
println(areaOrCircle("10"))
println(areaOrCircle("")) // error

入出力結果(Terminal, REPL(Read, Eval, Print, Loop))

$ scala-2.11 sample2.scala
3.14
314.0
java.lang.NumberFormatException: empty String
 at sun.misc.FloatingDecimal.readJavaFormatString(FloatingDecimal.java:1842)
 at sun.misc.FloatingDecimal.parseDouble(FloatingDecimal.java:110)
 at java.lang.Double.parseDouble(Double.java:538)
 at scala.collection.immutable.StringLike$class.toDouble(StringLike.scala:284)
 at scala.collection.immutable.StringOps.toDouble(StringOps.scala:30)
 at Main$$anon$1.areaOrCircle(sample2.scala:2)
 at Main$$anon$1.<init>(sample2.scala:8)
 at Main$.main(sample2.scala:1)
 at Main.main(sample2.scala)
 at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
 at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
 at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
 at java.lang.reflect.Method.invoke(Method.java:483)
 at scala.reflect.internal.util.ScalaClassLoader$$anonfun$run$1.apply(ScalaClassLoader.scala:70)
 at scala.reflect.internal.util.ScalaClassLoader$class.asContext(ScalaClassLoader.scala:31)
 at scala.reflect.internal.util.ScalaClassLoader$URLClassLoader.asContext(ScalaClassLoader.scala:101)
 at scala.reflect.internal.util.ScalaClassLoader$class.run(ScalaClassLoader.scala:70)
 at scala.reflect.internal.util.ScalaClassLoader$URLClassLoader.run(ScalaClassLoader.scala:101)
 at scala.tools.nsc.CommonRunner$class.run(ObjectRunner.scala:22)
 at scala.tools.nsc.ObjectRunner$.run(ObjectRunner.scala:39)
 at scala.tools.nsc.CommonRunner$class.runAndCatch(ObjectRunner.scala:29)
 at scala.tools.nsc.ObjectRunner$.runAndCatch(ObjectRunner.scala:39)
 at scala.tools.nsc.ScriptRunner.scala$tools$nsc$ScriptRunner$$runCompiled(ScriptRunner.scala:175)
 at scala.tools.nsc.ScriptRunner$$anonfun$runScript$1.apply(ScriptRunner.scala:192)
 at scala.tools.nsc.ScriptRunner$$anonfun$runScript$1.apply(ScriptRunner.scala:192)
 at scala.tools.nsc.ScriptRunner$$anonfun$withCompiledScript$1$$anonfun$apply$mcZ$sp$1.apply(ScriptRunner.scala:161)
 at scala.tools.nsc.ScriptRunner$$anonfun$withCompiledScript$1.apply$mcZ$sp(ScriptRunner.scala:161)
 at scala.tools.nsc.ScriptRunner$$anonfun$withCompiledScript$1.apply(ScriptRunner.scala:129)
 at scala.tools.nsc.ScriptRunner$$anonfun$withCompiledScript$1.apply(ScriptRunner.scala:129)
 at scala.tools.nsc.util.package$.trackingThreads(package.scala:43)
 at scala.tools.nsc.util.package$.waitingForThreads(package.scala:27)
 at scala.tools.nsc.ScriptRunner.withCompiledScript(ScriptRunner.scala:128)
 at scala.tools.nsc.ScriptRunner.runScript(ScriptRunner.scala:192)
 at scala.tools.nsc.ScriptRunner.runScriptAndCatch(ScriptRunner.scala:205)
 at scala.tools.nsc.MainGenericRunner.runTarget$1(MainGenericRunner.scala:67)
 at scala.tools.nsc.MainGenericRunner.run$1(MainGenericRunner.scala:87)
 at scala.tools.nsc.MainGenericRunner.process(MainGenericRunner.scala:98)
 at scala.tools.nsc.MainGenericRunner$.main(MainGenericRunner.scala:103)
 at scala.tools.nsc.MainGenericRunner.main(MainGenericRunner.scala)
$