thecodex.expert · The Codex Family of Knowledge
Free Course

Learn Java

Three tracks — from your first class to generics, concurrency, and virtual threads. Java 21 LTS. Free forever. No account.

🕐 ~16 hours3 tracksJava 21 LTS
Track 1

Foundations

Your first Java programs

  • Java syntax, types, and operators
  • Control flow and methods
  • Classes and objects
  • Arrays and ArrayList
  • Basic I/O and exceptions
🕐 ~4 hours5 lessons + quiz
Start Foundations →
Track 2

Practitioner

Write real Java programs

  • OOP: inheritance and interfaces
  • Collections and generics
  • Stream API and lambdas
  • Exception handling
  • I/O and NIO.2
🕐 ~5 hours5 lessons + quiz
Start Practitioner →
Track 3

Advanced

Think like a Java engineer

  • Concurrency: threads and locks
  • CompletableFuture and virtual threads
  • Records, sealed classes, pattern matching
  • JVM internals and GC
  • Kotlin introduction
🕐 ~7 hours5 lessons + quiz
Start Advanced →

After Java

Kotlin runs on the JVM alongside Java — 100% interoperable, null-safe, concise.

Kotlin Reference →