KITFORMA · EDITORIAL ANSWER
Why does deleting rows inside an enhanced for loop trigger ConcurrentModificationException?
KitForma editorial guide. The iterator and the collection can disagree about structural changes even when only one thread is involved. The exception name does not prove a race between threads.
Step-by-step answer
The iterator and the collection can disagree about structural changes even when only one thread is involved. The exception name does not prove a race between threads.
For a simple predicate, use
rows.removeIf(row -> row.isExpired()) on a mutable collection. If the algorithm needs iterator state, use an explicit iterator and its remove method after next. Do not modify the same collection independently while that iterator is active.
Test adjacent removable rows and a list where every row is removed; index-based fixes often skip neighbors. A fail-fast iterator is a diagnostic aid, not a synchronization mechanism. Shared access still needs a suitable concurrency design, and immutable collections cannot be made editable by switching loop syntax.Sources and verification
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