Java constant specific class body private variable access

Question

Why does this not compile, and (relatedly) why is it that CC cannot access what I would have thought (maybe I'm wrong) its own (private) member variable i, when AA and BB can indeed do so? How can CC access its own member variable?

Thank you.

enum TestEnum {
  AA(1000), BB(500), CC(100) {
    public int getI() {
      return i + 1;
    }
  };
  TestEnum(int i) {
    this.i = i;
  }

  private int i;
  public int getI() {
    return this.i;
  }
}

javac output:

TestEnum.java:6: error: non-static variable i cannot be referenced from a static context
                 public int getI() { return i + 1; }
                                            ^
1 error

why do you have `getI` twice? what's with the brackets around the first one ? the semicolon should come directly after `CC(100)` ... See: http://jdoodle.com/a/mQF — Nir Alfasi, Feb 14 '18 at 17:10
i is private, and technically you're making a subtype, would be my guess. Try super.getI instead of i. — Louis Wasserman, Feb 14 '18 at 17:14
That is probably the correct guess, but the output of of javac points to the fact that i is static, which does not makes sense at the moment. Another test could be making `i` `protected` instead of `private` — Luca Negrini, Feb 14 '18 at 17:17

Nikolas Charalambidis · Accepted Answer · 2018-02-14T17:24:07.173

3

Use super.getI() - 1 since you want to override the parent's method.

public enum TestEnum {
    AA(1000), BB(500), CC(100) {

        @Override
        public int getI() {
            return super.getI() - 1;
        }
    };

    private int i;

    TestEnum(int i) {
        this.i = i;
    }

    public int getI() {
        return this.i;
    }
}

Alternatively make the field protected to access it directly (return i - 1;) as @oleg cherednik suggests. However, I prefer the solution above.

edited Feb 14 '18 at 17:24

answered Feb 14 '18 at 17:17

Nikolas Charalambidis

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That was quick! Ah, of course. Thank you. That also suggests that each instance (or enum constant) of TestEnum is effectively a subclass, because subclasses also cannot access private variables of their superclass. Is that correct? – JL_SO Feb 14 '18 at 17:21
@HovercraftFullOfEels why? – JL_SO Feb 14 '18 at 17:35
@JL_SO: so you can 1) up-vote this answer and 2) probably accept it as well. – Hovercraft Full Of Eels Feb 14 '18 at 17:39
@HovercraftFullOfEels I have already tried to upvote it. I don't have enough points or whatever it is that they call it here. – JL_SO Feb 14 '18 at 17:43
Try again in 15 to 20 min – Hovercraft Full Of Eels Feb 14 '18 at 17:45

Oleg Cherednik · Answer 2 · 2018-02-14T17:35:10.470

You have two options: either do a protected field or call super.getId(). I prefer to do first one, it is easier to read. Note: think about enum body like parent class, and each constants like children, therefore your private field is not visible in children AA, BB, CC.

public enum TestEnum {
    AA(1000),
    BB(500),
    CC(100) {
        @Override
        public int getI() {
            return i + 1;
        }
    };

    protected final int i;

    TestEnum(int i) {
        this.i = i;
    }

    public int getI() {
        return i;
    }
}

P.S. It is preferable to have only final fields in the enum, because enum is like constant and should not have any variables.

I struggled to see what you'd changed here. You should add some text to your answer. — Michael, Feb 14 '18 at 17:27

Java constant specific class body private variable access

2 Answers2