快学Scala 第八课 （嵌套类）

嵌套类：

class Human {

  class Student{

    val age = 10

  }

}

object ClassDemo {

  def main(args: Array[String]): Unit = {

    val h = new Human

    val s = new h.Student

    println(s.age)

  }

}

有时会遇到这种情况：

class Human {

  class Student {

    def addS(s: Student) = {

      val ab = new ArrayBuffer[Student]()

      ab += s

    }

  }

}

object ClassDemo {

  def main(args: Array[String]): Unit = {

    val h = new Human

    val h2 = new Human

    val s = new h.Student

    val s2 = new h2.Student

    s.addS(s2)

  }

}

以上addS会报错，因为方法只能接收h.Student不能接收h2.Student。

解决方法有2个：

1. 类型投影

import scala.collection.mutable.ArrayBuffer

class Human {

  class Student {

    def addS(s: Human#Student) = {

      val ab = new ArrayBuffer[Human#Student]()

      ab += s

    }

  }

}

object ClassDemo {

  def main(args: Array[String]): Unit = {

    val h = new Human

    val h2 = new Human

    val s = new h.Student

    val s2 = new h2.Student

    s.addS(s2)

  }

}

2. 伴生对象

object Human {

  class Student {

  }

}

class Human {

    def addS(s: Human.Student) = {

      val ab = new ArrayBuffer[Human.Student]()

      ab += s

    }

}

object ClassDemo {

  def main(args: Array[String]): Unit = {

    val h = new Human

    val s = new Human.Student

    val s2 = new Human.Student

    h.addS(s)

    h.addS(s2)

  }

}

嵌套类要访问外部类有2种方式：

1. 外部类.this

class Human {

  val name = "Sky"

  class Student {

    println(Human.this.name)

    def addS(s: Student) = {

      val ab = new ArrayBuffer[Student]()

      ab += s

    }

  }

}

2. “自身类型”

class Human {

  outter =>

  class Student {

    println(outter.name)

    def addS(s: Student) = {

      val ab = new ArrayBuffer[Student]()

      ab += s

    }

  }

  val name = "Sky"

}