Java Performance Update: From JDK 21 to JDK 25
summary
JDK 25 vs 21 lists 13 concrete wins: energy drops ~24% on a Spring Boot workload, JIT and GC changes lift SPECjbb scores ~10% without recompilation, and a new preview Stable Value gives field-level immutability performance shortcuts. Built-in tracing adds finer method timing via JFR view tools and JMH drives reproducible regressions. ZGC goes generational for large heaps, AOT caching (leaden) speeds startup, and Compact Object Headers cuts per-object header by ~4 bytes, reducing heap by up to ~22% and CPU by ~8% in examples.
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chapters (9)
- 0:00Java performance discussion
- 1:39JDK 21 to JDK 25 performance
- 4:08Java performance metrics
- 13:47Java performance factors
- 23:41JVM compiler optimizations
- 33:10JDK 25 performance improvements
- 40:11Garbage collection optimizations
- 44:23Compressed object headers in JDK 25
- 45:28Q&A on language features and ZGC
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