Why this code is wrong and Java in a Nutshell said so? -

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i read java in nutshell now, , met question java in nutshell. example come book. see: e.g.: 

package de; public class {     protected string x; }  package uk; import de.*;  class b extends  { //first 1     public string getx(a a)     {         return "getx works" + a.x;//error: x has protected access in     }   //second 1     public string getx(b b)     {         return "getx works" + b.x; // works!     }    }

the author means because instances of b not have access arbitary instances of a. , if change code second one, compiler happy, because instances of same exact type can see each other’s protected fields. can not understand author's meaning, actually?

b extends a. x protected in a. b can access x's in b's.

b can not access x's in a's (that not b's).

consider class c extends a.

can see reasoning (objecte oriented principle) behind b's can't access c's x's.


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