Skip to content
JVM Atlas

Start here · the first lesson

What happens when you run a Java program?

Follow one small program from the text you type to the processor that runs it: the compiler, the class file, the JVM, memory, execution and garbage collection.

7 short chapters · about 21 minutes · no programming knowledge needed

Start chapter 1

Already know Java? Jump to any chapter, or explore the whole JVM.

  1. 1Your first Java programWhat is a Java program, before anything runs?
  2. 2The compilerHow does Hello.java become something the JVM can run?
  3. 3The JVMWhat is the JVM, and why does Java need one?
  4. 4Loading classesHow does the JVM get Hello.class ready to run?
  5. 5MemoryWhen your program creates an object, where does it go?
  6. 6ExecutionHow does the JVM actually run the bytecode?
  7. 7Garbage collectionWhat happens to objects your program no longer uses?
  8. What you now knowThe whole journey, in your own words, and a short check.
JVM Atlas

Explore the machine behind Java programs. A free, open-source atlas of the Java Virtual Machine. Specification baseline: Java SE 25. Implementation details: OpenJDK HotSpot, JDK 25.

MIT licensed · no accounts, no tracking, no backend · your progress stays in your browser.

JVM Atlas is an independent educational project and is not affiliated with or endorsed by Oracle. Java and OpenJDK are trademarks or registered trademarks of Oracle and/or its affiliates.