Java
Core Java fundamentals through modern Java features.
Core Java
OOP, SOLID, Object class, equality, Strings, immutability, wrappers, enums, records, sealed classes, var and pass-by-value.
Collection Framework
List, Set, Queue, Deque and Map implementations, HashMap internals, ConcurrentHashMap, load factor and fail-fast vs fail-safe iterators.
Java 8 & Streams
Streams from basics to internals: filter, map, sorting, reduce, collectors, groupingBy, flatMap, Optional, primitive streams, functional interfaces, method references, parallel streams, custom collectors, Spliterator and the java.time API.
Exception Handling
Checked vs unchecked, try-with-resources, custom exceptions, finally, suppressed exceptions, propagation, overriding rules, best practices and Spring Boot error handling.
Reflection
The Class class, obtaining Class objects, class loading internals, inspecting classes, constructors, fields and methods, annotations and dynamic proxies (JDK vs CGLIB).
Multithreading
Java concurrency from first principles to production: thread lifecycle, race conditions, synchronized, the Java Memory Model and volatile, wait/notify, deadlocks, explicit locks, atomics and CAS, executors and ThreadPoolExecutor sizing, CompletableFuture, synchronizers, concurrent collections, ThreadLocal, Fork/Join, virtual threads and Spring @Async.