Is it always a bad idea to use + to concatenate strings

Question

I have code as follows :

String s = "";
for (My my : myList) {
    s += my.getX();
}

Findbugs always reports error when I do this.

Answer 1

I would use + if you are manually concatenating,

String word = "Hello";
word += " World!";

However, if you are iterating and concatenating I would suggest StringBuilder,

StringBuilder sb = new StringBuilder();
for (My my : myList) {
    sb.append(my.getX());
}