Can't access protected members of a class from a subclass defined in a different package

Question

I am learning Java using the book Java: The Complete Reference. I am currently at chapter 9 and thus just inroduced to packages. On page 187, it says "If you want to allow an element to be seen outside your current package, but only to classes that subclass your class directly, then declare that element protected ". What I understand from this is, A subclass that resides in a package, say 'B', and extending a class that is defined as public inside another package 'A', having a member named "proc", then in order to make proc available in all subclasses, including subclasses defined outside the current package 'A', I have to mark it as protected. Now have a look at my implementation of the subclass defined inside package 'B':

package subapp;
import app.*;

public class Test extends App {

  public Test() { 
      App app = new App();
      System.out.println(app.proc); // error
   }
}

I am sure that all the packages (in both the class files) are loaded correctly, "direct" superclass of Test and its non-parameterized constructor, are publicly accessible, proc is marked as protected, and the main() function has no problem there. But I get a runtime exception when running subapp.Test that says "proc has protected access in /superclass path/. Am I getting the book statement wrong or the statement itself is wrong?

[Here](http://stackoverflow.com/a/33627846/276052) is a good table illustrating the basics of the `protected` access modifier. — aioobe, Jun 20 '16 at 10:06

Orin · Accepted Answer · 2016-06-01T17:33:41.030

0

You are already extending App, so you do not want to create a new App within the constructor. Instead, try something like this if the variable is protected.

public Test() {
   System.out.println(this.proc);
}

The reason it isn't working for you right now is you are making a new App within the constructor, and then trying to access that App's proc value directly, instead of through inheritance.

If the proc value is not correct through this, you might have to set it before the System.out.println(this.proc); Or you could call the super(); constructor before printing the value if the proc is getting initialized the the App constructor, such as:

public App() {
   proc = "test";
}

//.....

public Test() {
   super();
   System.out.println(this.proc);
}

edited Jun 01 '16 at 17:33

answered Jun 01 '16 at 17:28

Orin

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Thanks, that helped. But why can't I make use of the protected member the way I am doing in my code? I am still "inside" Test (a subclass) right? – Jun 01 '16 at 17:31
@Devashish You can call `super();` within the constructor if the parent constructor is initializing the variable `proc`. See my edit if that is the case. But the reason it doesn't work for the code you have right now is because even though you are inside `Test`(a subclass), you are trying to access the values of `App` outside of it's access modifier. `protected` values are only accessible to subclasses, so when you extend `App` you get direct access to all `protected` and `public` variables/methods without having to create a new instance of the object – Orin Jun 01 '16 at 17:37
Thanks...it's clear now :) – Jun 01 '16 at 17:38

Can't access protected members of a class from a subclass defined in a different package

1 Answers1