JRuntime AtlasJava platform fieldbook Enter fieldbook ↗

Java 25 LTS · language · JVM · production

Write the source.
Understand the machine.

A plain-language path from types and objects to virtual threads, bytecode, memory, security, observability, architecture, and safe delivery.

Start chapter 00 ↗Explore 100 concepts

SOURCE → JAVAC → BYTECODE → CLASS LOADER → JVM → JIT → MACHINE CODE

EXECUTION TRACE / LIVEJVM-25
Payment.java
record Payment(
  String id,
  BigDecimal amount
) {}

void reconcile(Payment p) {
  ledger.post(p);
}
01javaccompile + verify
→
02.classportable bytecode
→
03JIToptimize hot code
HEAPobjects
STACKSframes
METASPACEclasses
bytecode verifiedvirtual threads readyJFR recording
One learning system
20 detailed chapters
100 searchable concepts
30 retrieval drills
50 exam-style questions

Source to production

Learn Java as one connected runtime story.

Each chapter asks you to predict, run, inspect, and explain—not just memorize keywords.
  1. 01SpeakTypes, flow, methods, objects, records, and sealed modelsCh 00–04
  2. 02TransformGenerics, collections, lambdas, and stream pipelinesCh 05–08
  3. 03CoordinateResources, time, I/O, virtual threads, memory, GC, and JITCh 09–13
  4. 04ShipModules, security, tests, builds, performance, and observabilityCh 14–17
  5. 05ProveApply everything to LedgerStream and prepare for interviewsCh 18–19

Runtime mental model

A request enters.
Evidence comes out.

Open the JVM chapter →
  1. 01Class loader links trusted codeidentity + modules
  2. 02Virtual thread waits on I/Osimple blocking model
  3. 03Domain objects protect rulesrecords + sealed results
  4. 04JIT optimizes hot pathsprofile-guided machine code
  5. 05JFR records the evidencelatency + allocation + locks

Applied architecture

LedgerStream

Reconcile millions of financial records without losing a cent—or processing one twice.

Walk from requirements to domain model, file ingestion, exact money, virtual-thread concurrency, database limits, idempotency, checkpoints, JFR evidence, security, deployment, and disaster recovery.

Study the complete scenario ↗
INPUT FILE→VALIDATE→IDEMPOTENCY→LEDGER→RECONCILEBigDecimal · NIO · virtual threads · Semaphore · PostgreSQL · checkpoints · JFR

Retrieve and apply

Turn reading into engineering judgment.

Concept labSearch 100 Java concepts and practice 30 production decisions.Open workspace ↗ Full assessmentTake an original 50-question, two-hour OCP-style mock.Begin assessment ↗ Printable fieldbookRead the complete Feynman-style Java guide offline.Download PDF ↓

Do not stop at “it compiles.”

Know what your Java code makes the machine do.

Begin the fieldbook ↗