intermediate~2h
Collections: Mistakes That Pass Code Review But Fail in Production
A mistakes-and-fixes catalog of the collection bugs that compile cleanly, pass a quick glance in code review, and still cause ConcurrentModificationException, memory leaks, silent data corruption, or performance cliffs once real traffic and real data volumes show up.
Learning objectives
- Explain why modifying a collection during a for-each loop throws ConcurrentModificationException and how to fix it correctly
- Identify mutable-key bugs in HashMap/HashSet and explain why the entry becomes permanently unreachable
- Recognize static collections that only grow as a classic memory leak pattern and describe the fix
- Explain the performance cost of autoboxing inside collections of primitives
- Connect equals/hashCode mismatches to silent Set/Map misbehavior without re-deriving the full contract
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Collections: Mistakes That Pass Code Review But Fail in Production