Core Java OOP Concepts Java Basics & Keywords Strings & Immutable Objects Collections Framework Generics Exception Handling Multithreading & Concurrency Java 8+ Features (Lambdas, Streams, Optional, Date/Time API) JVM & Memory Management Advanced Java JDBC Servlets & JSP (basics) JMS (basics) Spring & Frameworks Spring Core (IoC, DI) Spring Boot (Auto-configuration, REST APIs) Spring Data JPA (Repositories, Relationships) Spring Security (Authentication, JWT) Microservices (Eureka, Config Server, API Gateway, Feign, Circuit Breaker) Database & SQL Joins & Aggregations Window Functions Indexing & Normalization Transactions & Isolation Levels Tools & Extras Maven/Gradle Git JUnit & Mockito Logging (SLF4J, Log4j, ELK basics) Design Patterns System Design Basics