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"
}
原文：http://www.cnblogs.com/AK47Sonic/p/7287198.html