JDK 27 delivers nine JEPs including G1 as universal default GC, compact object headers cutting heap usage by 25%, post-quantum TLS 1.3 enabled by default, plus preview features like lazy constants, primitive pattern matching, structured concurrency, and Vector API for AI workloads.
Java 27's preview feature extends switch expressions to all primitive types (long, float, double, boolean) and adds pattern matching with 'when' guards, enabling concise range-based business rules instead of if-else chains, though it remains a preview feature requiring explicit enablement.
Java 27 introduces four final features: G1 becomes the universal default garbage collector, compact object headers reduce memory overhead by 4 bytes per object, TLS 1.3 adds post-quantum hybrid key exchange by default, and JFR automatically redacts sensitive data like passwords and tokens before recording.
Java 27 introduces JFR in-process data redaction (JEP 536) that automatically masks sensitive values like passwords, tokens, and API keys in environment variables, system properties, and JVM arguments within flight recordings, using default glob patterns and allowing custom rules via FlightRecorderOptions, though custom JFR events and child processes remain unprotected.
The author explores Java 27's Structured Concurrency (StructuredTaskScope) for parallel service aggregation, showing how it replaces CompletableFuture with clearer lifecycle, automatic cancellation on failure, scope-level timeouts, and virtual threads, while noting it remains a preview API requiring --enable-preview.
