Easy Protected Member Question

[Edisandro Bessa]

Hi,

This question is from Complete Java 2 Certification Study Guide 5th Edition :

True or false: If class Y extends class X, the two classes are in different packages, and class X has a protected method called abby(), then any instance of Y may call the abby() method of any other instance of Y.

A. True
B. False

I chose true but the book states the correct answer as B.

Here's the explanation given by the author :

"An object that inherits a protected method from a superclass in a different package may call that method on itself but not on other instances of the same class."

I think the author is partially correct. The below code shows the opposite and compile and runs fine.

// File 1
package p1;
 
public class MyProtected {
    protected void doSomethingInParent(){
         System.out.println("Parent class");
    }
}
 

// File 2
 
package p2;
 
public class MyProtectedTest extends p1.MyProtected {
    p1.MyProtected m1 = new MyProtectedTest();
    MyProtectedTest m2 = new MyProtectedTest();
    
    void doSomethingInChild(){
       [B]//Does not compile. Cannot access a protected member outside
          // the package by using the super class instance.
          // Here the author is correct[/B]
        m1.doSomethingInParent(); 
 
        //[B]Compiles fine. It proves the opposite explained by the 
        //author. I can access a protected member within the subclass by
        //using another instance of the same class[/B]
 
        m2.doSomethingInParent();
 
       //[B]Also compiles fine. Confirmed by the author[/B]
        doSomethingInParent();     
    }
}

I think the author is partially correct or I'm missing something really important.

Any comments would be highly appreciated.

[Vijay Gade]

I think you are right too. From what I know, if class Super and Sub are in different packages, and Sub extends Super, then of course, you CANNOT access Super's protected members from Sub by using Super's references. But, you CAN use that Super's protected member by (1) directly calling that member, or (2) using a sub class reference.

-V

[Joerg Waldmann]

I think, you can even invoke private methods on a reference of the own class. So you can invoke protected methods as well.
But the point is, that you can not invoke private or protected methods on a reference of the parent class.