JDK 27 reaches first release candidate with nine new JEPs across four categories

JDK 27 finalizes nine JEPs, marking the feature set for this non-LTS release. The changes span four categories, with Core Java Library and HotSpot receiving the most updates. Engineers should note that these features are now locked in for the September release, though critical bug fixes may still be approved via the Fix-Request process. The absence of major last-minute additions suggests stability, but the non-LTS status means these features may evolve further before appearing in an LTS release.

The HotSpot updates introduce two defaults: G1 garbage collector and compact object headers. G1 becoming the default across all environments may improve memory management for applications previously using other collectors, but performance characteristics could shift. Compact object headers aim to reduce memory overhead, though the impact will vary by workload. Engineers should test these changes under realistic conditions, as defaults can expose edge cases not caught in earlier testing phases.

Security updates in JDK 27 include post-quantum hybrid key exchange for TLS 1.3 and PEM encodings for cryptographic objects. The post-quantum addition reflects growing industry concern about quantum computing threats, though its immediate utility depends on broader ecosystem adoption. PEM encodings, now in their third preview, simplify key and certificate handling but remain subject to change. Engineers working with cryptographic objects should evaluate these features for compatibility with existing tooling.

Preview and incubator features in JDK 27, such as Structured Concurrency and the Vector API, continue their iterative development. Structured Concurrency, now in its seventh preview, aims to simplify concurrent programming but remains experimental. The Vector API, in its twelfth incubator, still depends on Project Valhalla features before promotion. Engineers can experiment with these features but should avoid production use until they reach final status, as breaking changes are likely in future releases.