[Solved] What is the cost of + operation on a String in Java?

Java strings are immutable. Every time you do:

s+=c;

You’re really saying:

s = new String(s + c);

new String(s + c) must allocate a string of length s + 1, or:

1
2
3
4
5
6
7
8
9
…
etc.

Since Sum(1..N) == (n + 1) (n / 2), this is O(n^2).

One of the cases where StringBuilder is a definite advantage.