False positive SonarQube violation on String concatenation in loop

Question

I have some code looking like this (I replaced my business variables with generic ones):

Map<String, String> map = new HashMap<String, String>();
for (int i = 1; i < 10; i++) {
    String suffix1 = retrieveValue1(i);
    String suffix2 = retrieveValue2(i);
    String tag = "prefix";
    if (suffix1 != null) {
      tag += suffix1;
    }
    else {
      tag += suffix2;
    }
    map.put(tag.toUpperCase(), "on");
}

What bugs me is that I receive the following SonarQube violation:

Performance - Method concatenates strings using + in a loop

In my opinion this is a false-positive (because there is no real loop on a String here) but I'd like to double check first.

I could not find any similar case with my friend Google.

Is it a false-positive, or is there a real performance loss in my loop please?

Answer 1

Yes, SonarQube is probably getting confused about the use of += inside the loop.

String tag = "prefix"; is created inside the loop so there is no String concatenation inside a for loop and, technically, the warning is a false positive.

Note that you could still use StringBuilder to append both part of the tag, but you'd have to measure if it's necessary or not.