java - 为什么 protected 子类的不同包中的其他类私有(private)

Question

为什么 protected 对子类的不同包中的其他类私有(private)。但它仍然在父类(super class)的同一个包中受到保护。

package a;
class A
{
  protected a;
}

package b;
class B extends A
{
  B()
{
  System.out.println(a);
}
}

class C
{
  C()
  {
    System.out.println(new B().a);//error
   }

}

Answer 1

因为包是非相关类的protected访问修饰符的“可见性限制”。请在此处查看文档:http://docs.oracle.com/javase/tutorial/java/javaOO/accesscontrol.html :

The protected modifier specifies that the member can only be accessed within its own package (as with package-private) and, in addition, by a subclass of its class in another package.

从上面可以看出，你既不是子类的情况，也不是同包的情况。