intermediate~4h
Java 21: The Modern LTS Baseline
Java 21, the third LTS since Java 8, is where nearly everything previewed since Java 14 finally locks in at once: record patterns, finalized pattern matching for switch, and Sequenced Collections -- a genuinely new collection abstraction with real depth of its own -- plus virtual threads and structured concurrency shipping as finished features, covered in full elsewhere in this platform.
Learning objectives
- Explain why Java 21 is treated as the current practical baseline for new Java projects
- Use record patterns to destructure nested records directly in pattern matches
- Write exhaustive switch expressions over sealed hierarchies with no default branch required
- Use the SequencedCollection, SequencedSet, and SequencedMap interfaces and their first()/last()/reversed() operations
- Explain why Sequenced Collections were needed even though List already had an order
- Identify virtual threads and structured concurrency as Java 21 features and know they're covered in depth in the concurrency category
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Java 21: The Modern LTS Baseline