Does adding "final" makea class more thread safe

Question

I have a question about thread-safety. By adding final to the states variable, does it really make the class more thread safe? Since I am not doing anything with states but reading it I could as well forget about final?

class UnsafeStates {
  private String[] states = new String[] { "AK", "AL" /*...*/ };

  public String[] getStates() {
    return states;
  } 
}

It doesn't prevent anyone from doing `getStates()[0] = "i am evil"`. — Colonel Thirty Two, Dec 07 '15 at 14:03
It protects against `states = new...` not on the indexes however. — Emz, Dec 07 '15 at 14:33
http://stackoverflow.com/questions/7144915/final-fields-and-thread-safety — Dorus, Dec 07 '15 at 14:33
To answer the real question (see my link up here): Yes it does make it more thread safe. But no, as pointed out by all the answers below, it's not completely thread safe as the array itself can still be modified. — Dorus, Dec 07 '15 at 14:40

score 0 · Answer 1 · answered Dec 07 '15 at 14:04

0

Someone can still change the values with final. with states[1] = "something";

answered Dec 07 '15 at 14:04

Sean Powell

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score 0 · Answer 2 · answered Dec 07 '15 at 14:14

0

Even if you don't change the values of the array, it's not thread-safe because the array is not safely published. The final keyword is needed here to ensure that the initial value of the array is visible to other threads.

answered Dec 07 '15 at 14:14

fgb

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score 0 · Answer 3 · answered Dec 09 '15 at 10:34

So if i gave back another object with the same values like

    class UnsafeStates {
    private String[] states = new String[] { "AK", "AL" /*...*/ };

    public String[] getStates() {
    String[] states2 = new String[] { "AK", "AL" /*...*/ };
    return states2;
    } 
    }

it would be thread safe, right?

Does adding "final" makea class more thread safe

3 Answers3