In Java, can a class access the protected attribute in the super class of its super class?

Question

For example,

public class Question {
protected String question, correctAnswer, type;
....

}

public class MultipleChoice extends Question{{
  ...
}

public class TrueFalse extends MultipleChoice{
public TrueFalse(){
    this.type = "TrueFalse";
    this.question = "Question is not assinged!";
    this.correctAnswer = "Correct Answer is not assinged!";
}
....
}

It is clear that class MultipleChoice can access the question, type, and correctAnswer in class Question. But when I try to access them in class TrueFalse bythis.a. I got an error. cannot be resolved or is not a field.

Thus, is the protected attribute in a class is only accessible in its subclass, but not sub-subclass? Three files are in the same package but different class file.

Just for the record: you are sure multiple choice does not redeclare those fields? — GhostCat, Apr 30 '17 at 05:34
@GhostCat I actually used them in MultipleChoice's constructor. — Allen Yang, Apr 30 '17 at 05:37
its basically the definition of protected, any subclass of a class that can access a protected property can itself access the property. — chiliNUT, Apr 30 '17 at 05:41
Again: put up an [mcve]. Something that we could try to compile run ourselves. — GhostCat, Apr 30 '17 at 05:58
@GhostCat Oh, I didn't redeclare them in MultipleChoice class. Should I do that ? — Allen Yang, Apr 30 '17 at 06:05

Softy · Answer 1 · 2017-04-30T06:10:09.877

1

Yes it can. It's private methods that you can't access.

edited Apr 30 '17 at 06:10

answered Apr 30 '17 at 04:58

Softy

23
1
5

What do you mean onCreate its normal java pc application and not android – 0xDEADBEEF Apr 30 '17 at 04:59

score 0 · Accepted Answer · edited Jun 20 '20 at 09:12

0

Well, I copy/pasted your code into an online compiler and tried it out. It worked, and you can find it here. That looks like a yes.

I mean, if those were private fields it would make sense, but with the rest there shouldn't be a problem (unless it is package-access only).

Are you declaring those classes in the same file? If one of those is a nested class, that might be the cause.

Reply to old version

Super-super field access, uh? Hmm...

How about ((A)this).a? If the field is protected, maybe this could work.

NOTE: If it still doesn't work for you, try using it inside a non-static method inside C.

edited Jun 20 '20 at 09:12

Community

1
1

answered Apr 30 '17 at 04:53

DragShot

341
2
10

@AllenYang where are you exactly writing the code to access field `a`? – DragShot Apr 30 '17 at 04:57
@AllenYang I just copy/pasted into a generic online compiler and ran it without warnings. – DragShot Apr 30 '17 at 05:30
it is wired. Actually I also used protected data in the constructor of MultipleChoice. Is that a reason? – Allen Yang Apr 30 '17 at 05:39

BHAR4T · Answer 3 · 2017-04-30T06:10:52.397

0

public class MultilevelVar {
public static void main(String[] args) {
new C().fun();
}
}

class A {
protected int x = 10;
}

class B extends A {
int x = 20;
}

class C extends B {
int x = 30;
void fun() {
System.out.println(((A) this).x);
System.out.println(((B) this).x);
System.out.println(((C) this).x);
}
}

edited Apr 30 '17 at 06:10

answered Apr 30 '17 at 05:39

BHAR4T

338
3
14

You can use variable from _n_ level of hierarchy. – BHAR4T Apr 30 '17 at 05:43
Yes, I'm declaring new x in each level. – BHAR4T Apr 30 '17 at 06:01
1

And that is not the point. A protected field is visible from subclasses by default. Your example is shadowing the inherented protected field by creating another field withe the same name! – GhostCat Apr 30 '17 at 06:48

In Java, can a class access the protected attribute in the super class of its super class?

3 Answers3

Reply to old version