Java Programming Deep Dives 1. ConcurrentHashMap Internals Explain segment locking, CAS operations, and Java 8+ optimizations (treeify buckets). Compare with HashMap/Hashtable. 2. Thread-Safe Singleton Implementations Compare eager initialization, double-checked locking, and enum singleton. Discuss broken pre-Java 5 implementations. 3. Java Memory Model (JMM) Explain visibility guarantees, reordering rules, and how volatile/synchronized enforce memory barriers. 4. Garbage Collection Algorithms Contrast G1, CMS, and Serial GC. Discuss pause times, throughput, and use cases (low-latency vs. batch processing). 5. Immutable Object Design Implement immutability for complex objects. Discuss final fields, defensive copying, and thread-safety benefits. 6. HashMap vs. ConcurrentHashMap Compare synchronization strategies (entire map vs. segmented locks), null handling, and performance trade-offs. 7. Autoboxing Pitfalls Explain Integer cache behavior (e.g., == vs. equals()). Discuss performance penalties for frequent unboxing. 8. Class Loading & Custom Class Loaders Describe bootstrap/extension/application class loader hierarchy. Write a basic custom class loader to load classes from non-standard sources. 9. Fork/Join Framework Implement parallel computation for tasks like array sum. Compare with ExecutorService and discuss work-stealing efficiency. 10. Phantom/Soft/Weak References Explain reference types, JVM retention policies, and use cases (caching, memory-sensitive apps).