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必须覆盖scala中的val变量

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我在scala中遇到了一个奇怪的问题 . 以下是我的代码，类Employee扩展类Person

但是这段代码无法编译，我已经明确地将firstName和lastName定义为val变量 . 这是为什么 ？这是否意味着我必须覆盖基类中的val变量？目的是什么？

class Person( firstName: String,  lastName: String) {

}

class Employee(override val firstName: String, override val lastName: String, val depart: String)
    extends Person(firstName,lastName){

}
scala

4 回答

  • 6

    构造函数的输入参数不是val，除非你说它们 . 如果它们已经存在，为什么要覆盖它们呢？

    class Person(val firstName: String, val lastName: String) {}
class Strange(
  override val firstName: String, override val lastName: String
) extends Person("John","Doe") {}
class Employee(fn: String, ln: String, val depart: String) extends Person(fn,ln) {}

    如果它们不是val并且您想要制作val，则不需要覆盖：

    class Person(firstName: String, lastName: String) {}
class Employee(
  val firstName: String, val lastName: String, val depart: String
) extends Person(firstName,lastName) {}
    回复于
  • 10

    由于构造函数参数在Person中没有val / var声明，并且Person不是case类，因此参数不是Person类的成员，只是构造函数参数 . 编译器基本上告诉你：嘿，你说，firstName和lastName是成员，它覆盖/重新定义从基类继承的东西 - 但据我所知，没有任何东西......

    class Person(val firstName: String, val lastName: String)
class Employee(fn: String, ln: String, val salary: BigDecimal) extends Person(fn, ln)

    你不需要在这里声明firstName / lastName作为覆盖，顺便说一下 . 简单地将值转发到基类的构造函数就可以了 .

    回复于
  • 0

    您也可以考虑尽可能多地将超类重新设计为特征 . 例：

    trait Person {
  def firstName: String
  def lastName: String
}

class Employee(
  val firstName: String,
  val lastName: String,
  val department: String
) extends Person

    甚至

    trait Employee extends Person {
  def department: String
}

class SimpleEmployee(
  val firstName: String,
  val lastName: String,
  val department: String
) extends Employee
    回复于
  • 1

    除非我've misunderstood your intention, here' s如何扩展 Person .

    Welcome to Scala version 2.8.0.final (Java HotSpot(TM) Client VM, Java 1.6.0_21).
Type in expressions to have them evaluated.
Type :help for more information.

scala> class Person( firstName: String, lastName: String)
defined class Person

scala> class Employee(firstName: String, lastName: String, depart: String) extends Person(firstName, lastName)
defined class Employee
    回复于

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