以下代码显示Jack在建筑行业受雇,但Jane是经济不景气的又一受害者:
为什么比赛无法将Jane识别为学生?
abstract class Person(name: String) {
case class Student(name: String, major: String) extends Person(name)
override def toString(): String = this match {
case Student(name, major) => name + " studies " + major
case Worker(name, occupation) => name + " does " + occupation
case _ => name + " is unemployed"
}
}
case class Worker(name: String, job: String) extends Person(name)
object Narrator extends Person("Jake") {
def main(args: Array[String]) {
var friend: Person = new Student("Jane", "biology")
println("My friend " + friend) //outputs "Jane is unemployed"
friend = new Worker("Jack", "construction")
println("My friend " + friend) //outputs "Jack does construction"
}
}
为什么比赛无法将Jane识别为学生?
friend
是一个Narrator.Person
,但不是一个friend.Person
。 - Alexey Romanov