StringBuilder vs StringBuffer: what's the difference and which is better to use in Java?

Hi everyone! I started learning Java and often encounter situations where I need to concatenate many strings, especially in loops. At first I used regular concatenation with `+`, but I read that it's inefficient and it's better to use `StringBuilder` or `StringBuffer`. However, I'm confused: what's the difference between them? They both seem to do the same thing — allow you to build a string without creating extra objects. I wrote a small example but don't understand which one to choose: ```java public class Test { public static void main(String[] args) { // Option 1 StringBuilder sb = new StringBuilder(); for (int i = 0; i < 1000; i++) { sb.append("number ").append(i).append(", "); } String result1 = sb.toString(); // Option 2 Stri