Can't access protected inner class while inheriting

Question

Reading through "Thinking in Java" i stuck in ex:6 of Inner Classes chapter.

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Exercise 6: (2) Create an interface with at least one method, in its own package. Create a class in a separate package. Add a protected inner class that implements the interface. In a third package, inherit from your class and, inside a method, return an object of the protected inner class, upcasting to the interface during the return.

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This is my code:

IOne.java

interface

package intfpack;
public interface IOne{
        void    f();
}

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COne.java

Class with protected inner class that implements the interface

package classpack;
import intfpack.*;
public class COne{
        protected class Inner implements IOne{
                public void f(){System.out.println("Inner class of COne");}
        } 
}

---

CTwo.java

Inheriting from class with protected inner class

package thirdpack;
import classpack.*;
import intfpack.*;

public class CTwo extends COne{
        public IOne getInner(){
                IOne io = new Inner(); 
                return io;
        }
        public static void main(String[] args){
                CTwo ct = new CTwo();
                ct.getInner();
        }
}

Copmiler says next:

javac CTwo.java
CTwo.java:9: Inner() has protected access in classpack.COne.Inner
                IOne io = new Inner(); 
                          ^
1 error

But the book says that i can access protected inner classes in derived class. Where is mistake?

Answer 1

The error message is complaining about the constructor being protected, not the class. But you haven't explicitly defined a constructor in the code you posted. In this case, according to the JLS, the default constructor will be protected (the same as the class).