Core Java: Multithreading, Collections Framework, Exception Handling, Java 8+ features
OOP Concepts: Inheritance, Polymorphism, Encapsulation, Abstraction with real examples
Spring Boot: Auto-configuration, Dependency Injection, Spring MVC, REST Controllers
Database: JPA/Hibernate, Transactions, Connection Pooling, Query Optimization
REST APIs: Design principles, HTTP methods, Status codes, Security (JWT/OAuth)
Problem-Solving: Algorithm challenges, System design scenarios, Debugging exercises