StringBuilder vs String concatenation in toString() in Java

Version 1 is preferable because it is shorter and the compiler will in fact turn it into version 2 - no performance difference whatsoever.

More importantly given we have only 3 properties it might not make a difference, but at what point do you switch from concat to builder?

At the point where you're concatenating in a loop - that's usually when the compiler can't substitute StringBuilder by itself.

The key is whether you are writing a single concatenation all in one place or accumulating it over time.

For the example you gave, there's no point in explicitly using StringBuilder. (Look at the compiled code for your first case.)

But if you are building a string e.g. inside a loop, use StringBuilder.

To clarify, assuming that hugeArray contains thousands of strings, code like this:

...
String result = "";
for (String s : hugeArray) {
    result = result + s;
}

is very time- and memory-wasteful compared with:

...
StringBuilder sb = new StringBuilder();
for (String s : hugeArray) {
    sb.append(s);
}
String result = sb.toString();