Java 多级继承 - 一级类中 protected 实例变量

Question

我有一个问题属于 Java 中的多级继承。所有三个类都在同一个包中

我有 A 类:

public class A {
   protected int x;
}

public class B extends A {
   public void doSomething {
      // x is visible.agreed, as it is a direct subclass of A
   }  
}


public class C extends B {
   public void doSomething {
      // x is still visible, how come? I mean it is at the 2nd level 
     //  I am confused why?
   }  
}

喜欢有什么意义吗？或者这是我们必须默认采取的行为？

Answer 1

用 protected 修饰符标记的变量/方法对同一包中的所有类可见，并且仅对不同包中的子类可见。 以下是示例。

package a;
class A{
protected int x;
}
class B extends A{
//x can be accessed from this class
} 

class C extends B {
//x can be accessed from this class
}
class D{
//x can be accesed this class but you will have to create A's instance 
}

package B 
class One {
//cannot access x from this class
}
class Two extends A {
//can access x from this class
}