Java
Core language depth: concurrency, the JVM, collections and the design judgment senior interviews test hardest.
1. Concurrency & Multithreading
Threads, locks, the memory model and thread pools — the topic most senior Java interviews live or die on.
2. JVM Internals & Garbage Collection
Memory areas, generational GC, collector selection, leak hunting and JIT — what actually happens under your code.
3. Collections Framework Internals
HashMap internals, the equals/hashCode contract, complexity trade-offs and concurrent collections.
4. Generics & the Type System
Type erasure, wildcards and PECS, variance, and designing APIs that are both flexible and safe.
5. Functional Programming & Streams
How streams really execute, parallel pitfalls, Optional discipline and the collector toolkit.
6. OO Design, SOLID & Patterns
SOLID at system scale, composition vs inheritance, immutability and knowing when patterns become noise.
7. Exceptions & Resource Management
Checked vs unchecked strategy, try-with-resources, and designing error handling for layered systems.
8. Modern Java (9 → 21+)
Virtual threads, records, sealed types and pattern matching — plus how to actually migrate a fleet.