advanced~3h
Collections Interview Deep Dive
A capstone topic tying the Collections Framework together through the lens of the interview questions that actually get asked — implementing a simplified HashMap, explaining why String makes a good hash key, the real root cause of ConcurrentModificationException, fail-fast versus fail-safe iteration, and when a senior engineer would genuinely reach for a TreeMap in production.
Learning objectives
- Implement a simplified HashMap from scratch to demonstrate real understanding of buckets, hashing, and collision handling
- Explain precisely why String's immutability and cached hash code make it an excellent hash key
- Trace the exact mechanism behind ConcurrentModificationException down to the modCount field
- Distinguish fail-fast iteration (ArrayList, HashMap) from fail-safe iteration (CopyOnWriteArrayList, ConcurrentHashMap) and the trade-offs each implies
- Justify choosing a TreeMap over a HashMap in a real system design scenario, not just as a textbook fact
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Collections Interview Deep Dive