在scala中，类和它的伴生对象可以相互访问对方的私有对象
class Person {
private var _age = 2
def age_=(num: Int) = this._age = num
def age = _age
def printObj { println(s"I can see ${Person.obj}") }
}
object Person {
// access the private class field 'age'
def double(p: Person) = p._age * 2
private val obj = "Person's object"
}
object Driver extends App {
//伴生对象可以引用类的私有变量
val p = new Person
println(p.age)
p.age = 10
println(Person.double(p)) // prints 20
//类可以引用伴生对象的私有变量
p.printObj //prints I can see Person's object
}
