ConcurrentModificationException in Java — What It Means and How to Fix It

ConcurrentModificationException is thrown when a collection is structurally modified while it's being iterated over, outside of the iterator's own methods.

Key points

• Read the full stack trace from the top — it names the exact class, method, and line where the exception originated

Example

Common when calling list.remove() directly inside a for-each loop over that same list — use an Iterator's remove() method instead