If you want to master Java fast? Stop “learning Java” and start shipping small things daily.
1. Core syntax OOP: classes, interfaces, generics, immutability
2. Collections: List/Map/Set, equals/hashCode, iterators, Big-O basics
3. JVM basics: memory, GC, stack vs heap, classloading (at least conceptually)
4. Concurrency: threads, executors, synchronized/locks, CompletableFuture
5. I/O: files, streams, NIO, serialization pitfalls
6. Testing: JUnit, mocking, writing tests for bugs you just fixed
7. Build/tools: Maven or Gradle, logging (SLF4J), debugging in IDE
8. Modern Java: streams, Optional, records, sealed classes (know when not to use them)
Rule: 60 mins reading, 120 mins coding, 30 mins debugging every day.
Pick one backend project (REST API DB) and use it to practice every topic.