Question

I am reading Thinking In Java at the moment and I encountered one small problem. I am doing exercise 12 from chapter 8.

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.

So I created these .java files:

A.java

    package c08;
    public interface A
    {
        void one();
    }

Pr2.java

    package c082;
    import c08.*;
    public class Pr2 
    {
        protected class InPr2 implements A
        {
           public void one() {System.out.println("Pr2.InPr2.one");}
           protected InPr2() {}
        }
    }

Ex.java

    package c083;
    import c082.*;
    import c08.*;
    class Cl extends Pr2
    {
        A foo() 
        {
            InPr2 bar=new InPr2();
            return bar;
        } 
    }

And my NetBeans IDE underlines

    InPr2();

and says that:InPr2() has protected access in C082.Pr2.InPr2 and I am wondering why.
If I didn’t explicitly state that constructor in InPr2 should be protected it would be only accessible in C082 package, but when I am inheriting class Pr2 shoudn’t it be available in class Cl, because InPr2 is protected? Everything is fine when I change constructor to public.

Answer 1

It should work just fine as you have it, except changing the protected InPr2() {} to public InPr2() { }. In other words “Anyone can instantiate this class IF they can see the class to begin with.”