Core Java · from your first line of code to the JVM
Learn Java properly.
From zero to how the JVM really works.
Start from zero: no programming experience needed, and every word is explained in plain English. Each topic goes all the way down, from an everyday analogy to what the compiler and the JVM really do, with examples you can edit and run right on the page, mistakes to make on purpose, and interview answers. Every feature is tagged with the Java version that introduced it (Java 8, 11, 17, 21, 25), so you always know what you can use where.
- Phases
- 17
- Topics
- 149
- Hours
- 74
- Diagrams
- 0
- Exercises
- 1172
By the end you can
What this course makes you able to do
- Write, compile and run Java programs, and read compiler errors and stack traces with confidence
- Explain what happens in memory: stack, heap, references, pass-by-value, garbage collection
- Design with classes, interfaces, records, enums and sealed types, and know when to use each
- Use generics, collections, lambdas and streams fluently, and know how HashMap and ArrayList work inside
- Write correct concurrent code with threads, executors, CompletableFuture and virtual threads
- Answer Core Java interview questions in depth, version by version from Java 8 to Java 25
Beginner → Advanced
The curriculum, by level
Beginner
Intermediate
Where should I start?
Pick a path for your goal
Complete beginner
Never programmed before. Start at the very first topic: every word is explained.
Job-ready Java developer
You know the basics and want the depth employers test.
Senior and interviews
You use Java daily and want internals and modern Java.