Interview, certification, and glossary
Oracle currently lists the Java SE 21 Developer Professional exam
1Z0-830. Oracle's learning path describes a two-hour online
exam, and the official practice exam uses 68% as its practice passing
target. Oracle describes the exam as multiple-choice with code snippets
that test output, compilation, and practical behavior.
This site's 50-question, 120-minute assessment is original OCP-style practice. It targets Java 21 certification concepts while the broader fieldbook teaches Java 25 LTS production engineering. Always verify Oracle's live exam page before purchasing because delivery details can change.
Interview frame: BYTECODE
- Business: users, invariants, throughput, security, recovery.
- Your types: records, classes, interfaces, generics, nullability.
- Tasks: algorithms, collections, streams, threads, cancellation.
- Errors: validation, exceptions, retries, partial failure.
- Concurrency: ownership, locks, visibility, virtual threads, limits.
- Operations: JVM, memory, GC, JFR, logs, metrics, packaging.
- Dependencies: modules, libraries, supply chain, external systems.
- Evidence: tests, benchmarks, profiles, restore and failure drills.
Essential terminology
| Term | Meaning |
|---|---|
| JDK / JVM | Development kit / virtual machine |
| JLS / JVMS | Language / virtual-machine specification |
| JAR | Java archive |
| JIT | Just-in-time compiler |
| GC | Garbage collection |
| JFR / JMC | Flight Recorder / Mission Control |
| JPMS | Java Platform Module System |
| API / SPI | Application / service-provider interface |
| NIO | New I/O APIs including Path, Files, channels, buffers |
| TWR | Try-with-resources |
| PECS | Producer Extends, Consumer Super |
| happens-before | Memory-model ordering and visibility guarantee |
| LTS | Long-term-support release |
| SBOM | Software bill of materials |
| SLI / SLO | Service measurement / reliability target |
| RPO / RTO | Tolerated data loss / restoration time |
Final Feynman challenge
Explain one LedgerStream transaction from input bytes to parsed record, domain validation, concurrent matching, checkpoint, report, metrics, and recovery. Then explain which memory is shared, which resource is bounded, which exception is recoverable, and which tool proves performance. Anything unclear is your next study target.