Strings, Regex & Java 8+ Features — quiz

You're building a long error message by concatenating values inside a loop with `msg += line;`. Why might a reviewer push you toward StringBuilder?

• Plain `+=` doesn't compile inside loops
• String is immutable, so each `+=` allocates and copies a new String — O(n²) for the whole loop. StringBuilder mutates a backing buffer, making the same work O(n)
• StringBuilder is required for thread-safety
• `+=` only works for numeric types