javademos/lazy-constants

lazy-constants — Lazy Constants (JEP 531, third preview in JDK 27)

Companion code for the ankurm.com article Lazy Constants in JDK 27 (JEP 531): Replacing Double-Checked Locking. The explanation lives in the article; this folder holds the runnable sources and the transcripts they produced.

JDK25=/path/to/jdk-25 JDK26=/path/to/jdk-26 JDK27=/path/to/jdk-27 [JDK21=/path/to/jdk-21] ./run.sh    # regenerates output/*.txt
RUN_JMH=0 ./run.sh                                                                                      # skip the 3-minute benchmark

• src/ — OldWays (holder idiom and double-checked locking, plain Java), Basics, ToStringStates, Service, Failures, LazyCollections (JDK 27, --enable-preview), StableValue25 (the JDK 25 API).
• broken/ — code that fails to compile on purpose: the old StableValue name, the two methods removed in 27, no --enable-preview, a set that does not exist.
• jmh/ — a JMH 1.37 benchmark of the read path. ./jmh/fetch.sh downloads the jars from Maven Central and checks their sha1; they are not committed. ./jmh/run-jmh.sh writes output/07-jmh.txt.

Everything except the JMH numbers is byte-stable. The JMH numbers are machine dependent: treat them as shape, not results.

Tested on Temurin 25.0.4.1+1, 26.0.2.1+1 and 27+35, and OpenJDK 21.0.10 for the plain-Java baseline.