Scala 範例程式 - 屬性的錯誤處理 (Timeofday)

原始程式：timeofday.scala

object timeofday {
  class DateError extends Exception

  /** Simulating properties in Scala 
   *  (example 4.2.1 in ScalaReference.pdf) 
   */
  class TimeOfDayVar {
    private var h, m, s: Int = 0

    def hours = h

    /** A method 'ident_=' is a setter for 'ident'. 'code.ident = ...' will 
     *  be translated to a call to 'ident_=' 
     */
    def hours_= (h: Int) =
      if (0 <= h && h < 24) this.h = h
      else throw new DateError()

    def minutes = m
    def minutes_= (m: Int) =
      if (0 <= m && m < 60) this.m = m
      else throw new DateError()

    def seconds = s
    def seconds_= (s: Int) =
      if (0 <= s && s < 60) this.s = s
      else throw new DateError()
  }

  def main(args: Array[String]) {
    val d = new TimeOfDayVar
    d.hours = 8; d.minutes = 30; d.seconds = 0
    d.hours = 25 // throws a DateError exception
  }
}

執行結果：

D:\scala>scalac timeofday.scala

D:\scala>scala timeofday
timeofday$DateError
        at timeofday$TimeOfDayVar.hours_$eq(timeofday.scala:17)
        at timeofday$.main(timeofday.scala:33)
        at timeofday.main(timeofday.scala)
        at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
        at sun.reflect.NativeMethodAccessorImpl.invoke(Unknown Source)
        at sun.reflect.DelegatingMethodAccessorImpl.invoke(Unknown Source)
        at java.lang.reflect.Method.invoke(Unknown Source)
        at scala.tools.nsc.ObjectRunner$$anonfun$run$1.apply(ObjectRunner.scala:
75)
        at scala.tools.nsc.ObjectRunner$.withContextClassLoader(ObjectRunner.sca
la:49)
        at scala.tools.nsc.ObjectRunner$.run(ObjectRunner.scala:74)
        at scala.tools.nsc.MainGenericRunner$.main(MainGenericRunner.scala:154)
        at scala.tools.nsc.MainGenericRunner.main(MainGenericRunner.scala)