The member `s' in class My is not `protected' at all;
it is package-private.  If you want it to be `protected',
you need to say so when you declare it.

Eric gave you the right answer, but to clarify a bit...

When you didn't declare "String s" as private, protected or public in
your parent class, it defaulted to private.  Make sure "s" is declared
as protected in the PARENT class.  Then, when you create your child
class, you don't need to create that protected "s" variable.  Instead,
all you need to do is...

public class Test extends My{
 public static void main(String[] args){
   My my = new My();
   System.out.println(my.s);
 }
}

Because "s" is now protected in the parent, it can be accessed this
way.  However, this really doesn't make too much sense (in terms of
use).  Instead, by extending "My" your Test class has its own "s"
variable (because Test is a My).  Try it...

public class Test extends My {
 public static void main(String[] args) {
   this.s = new String("Test has s");
   System.out.println(this.s);
 }
}

I'd recommend looking for inforamtion on Google for the differences
(especially with scope) in terms of public/protected/private modifiers.