如何从另一个 package 访问受保护的内部 class？

Question

How do I access inner class "Inner" in "file1" in package "secret" from "file2" in package "test". Here is the code for it:

package secret;

public class file1 {
    protected class Inner {
        public int x = 8;
    }
}

package test;
import secret.file1;

public class file2 {
    public static void main(String[] args) {
        // code
    }
}

I am aware that there is a similar question on this topic ( How to access protected inner class outside package? ) but I didn't seem to understand the answers. Here is what I have tried so far (from reading the answers):

First attempt:

public class file2 extends file1 {
    public static void main(String[] args) {
        file1 outer = new file1();
        file1.Inner inner = outer.new Inner();
    }
}

Second attempt:

public class file2 extends file1 {
    public static class file3 extends file1.Inner {
        public static void main(String[] args) {
            file1 outer = new file1();
            file1.Inner inner = outer.new Inner();
        }
    }
}

Attempt 3:

public class file2 extends file1 {
    public static class file3 extends file1.Inner {
        public static void main(String[] args) {
            file2 outer = new file2();
            file2.file3 outerinner = outer.new file3();
            file2.file3.Inner inner = outerinner.new Inner();
        }
    }
}

There definitely seems like I'm missing something, guiding me in the right direction would be much apricated.

Answer 1

There's a workaround by using third class:

package secret;

public class file3 extends file1 {
    public Inner createInner(){
        return new Inner();
    }
}

then simply:

public class file2 extends file1 {
    public static void main(String[] args) {
        file3 outer = new file3();
        file1.Inner inner = outer.createInner();
    }
}

Answer 2

check your class hierarchy design whether it cannot be simplified.put your main focus on the difference between inner and static nested classes. or come up with something like this file1 x = new inner();

Answer 3

Change the visibility to public. Inner classes are mostly for interacting with private fields in its parent class anyway.

Other way you can use a protected inner class is if the class you want to use it on is a sub class. That is,the parent class of the inner class is being inherited by the class you want to use it on. in your case

    package secret;
    
    public class file1 {
        protected class Inner {
            public int x = 8;
        }
    }

    package test;
    import secret.file1;
    
    public class file2 extends file1 {
        public static void main(String[] args) {
            File1 f = new File1();
            File1.Inner g = f.new Inner();
            System.out.println(g.x);
        }
    }