Interview Prep · Phase 3
What is actually inside the collection you picked: array growth and copying, hash buckets and treeification, red-black trees, the difference between a fail-fast and a fail-safe iterator, and the memory each structure really costs per element.
The interface hierarchy and what each contract promises, why some methods throw UnsupportedOperationException by design, and the differences between Arrays.asList, List.of and List.copyOf.
Read tutorialWhat each one stores in memory, the 1.5x growth and array copy, why LinkedList loses even at insertion in the middle, and the per-element overhead that makes cache locality decide the winner.
Read tutorialHow HashMap stores entries, why the hash is XORed with its own high bits, what happens during a resize, when a bucket becomes a red-black tree, and the Java 7 race that caused infinite loops.
Read tutorialHow ConcurrentHashMap achieves concurrency without a global lock, why segments disappeared in Java 8, the computeIfAbsent deadlock, and why size() is only an estimate.
Read tutorialHow TreeMap uses a red-black tree for sorted keys and range queries, how LinkedHashMap adds a doubly-linked list for ordering, and building an LRU cache in ten lines with removeEldestEntry.
Read tutorialWhy every Set is a Map underneath, how iteration order differs, the TreeSet comparator-equality trap, EnumSet as a bit vector, and choosing a Set for concurrent access.
Read tutorialThe three method families and why Queue has three ways to insert, choosing between ArrayBlockingQueue and LinkedBlockingQueue, PriorityQueue as a binary heap, and the SynchronousQueue handoff.
Read tutorialHow modCount makes an iterator fail fast, why removing inside a for-each throws, the four correct ways to remove while iterating, and what weakly consistent iteration actually promises.
Read tutorialA complete Big-O table for every common collection, what each one actually costs per element in bytes, why boxing dominates numeric collections, and a decision procedure that fits on one page.
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