What You Should Know Now — and What's Next

What You Should Know Now

• Core syntax: variables, primitive types, control flow, arrays, methods
• Object-oriented programming: classes, inheritance, polymorphism, interfaces, and encapsulation done properly
• The Collections Framework, generics, lambdas, and streams
• Exception handling, file I/O, and basic multithreading
• Modern language features: records, sealed classes, and pattern matching
• Concurrency in depth, JVM fundamentals, JDBC, and building a REST API with Spring Boot
• How a production Java service is tested, packaged, and deployed

What Should You Learn Next?

• Spring Boot in depth — dependency injection, Spring Data JPA, and Spring Security, building directly on the REST API lesson above.
• Kotlin — a JVM language fully interoperable with Java, now the default choice for new Android development.
• A related language — C#, a close sibling with a very similar type system and OOP model, if working across the .NET ecosystem interests you.
• Distributed systems basics — once one service works well, learn how several communicate reliably (message queues, service discovery, observability).

Build Something

Pick a project idea that solves an actual problem you personally have — and build it as a small Spring Boot service backed by a real database, with a JUnit test suite alongside it from the start.