Java 12 is a non-LTS feature release. It was the first Java release to include a preview language feature, enabled only with the –enable-preview compiler and JVM flag. Java 12 is end-of-life since September 2019.
| Release Date | March 19, 2019 |
| LTS | No |
| OpenJDK End-of-Life | September 17, 2019 |
| Notable for | First release with preview features (JEP 12) |
Java 12 is end-of-life. Organizations running it should upgrade to a current LTS release: Java 17, Java 21, or Java 25.
Switch Expressions (Preview, JEP 325)
The first preview language feature in Java. Switch can now be used as an expression that returns a value, with arrow syntax for single-line branches. This was the preview; switch expressions were finalized in Java 14 (JEP 361).
// Java 12 preview syntax (required –enable-preview)
int numLetters = switch (day) {
case MONDAY, FRIDAY, SUNDAY -> 6;
case TUESDAY -> 7;
case THURSDAY, SATURDAY -> 8;
default -> throw new IllegalStateException(“Unexpected: ” + day);
};
JVM Constants API (JEP 334)
A standard API for modeling nominal descriptors of class-file and runtime artifacts: classes, methods, fields, and constant pool entries. The java.lang.constant package provides types like ClassDesc, MethodTypeDesc, and MethodHandleDesc. Used internally by condy (dynamic constants, JEP 309, Java 11) and the java.lang.invoke API.
This API is primarily for compiler and runtime authors. Application developers rarely interact with it directly.
Shenandoah Garbage Collector (JEP 189)
Low-pause garbage collector from Red Hat. Shenandoah performs evacuation work concurrently with running application threads, targeting pause times independent of heap size. An application with a 100 GB heap sees similar pause times to one with a 1 GB heap.
Shenandoah was an experimental feature in Java 12. It became production-ready in Java 15 (JEP 379). In Java 25, it gained generational mode (JEP 521).
| Change | Description |
|---|---|
| Default CDS Archives | JVM ships with a default class-data-sharing archive, improving startup time without manual java -Xshare:dump |
| Microbenchmark Suite | Added JMH-based microbenchmark suite to the OpenJDK source tree for contributor use |
| Compact Number Formatting | java.text.NumberFormat supports compact representations like “1K” and “1M” via getCompactNumberInstance() |
| Teeing Collector | Collectors.teeing() forwards stream elements to two downstream collectors and merges their results |
Java 12 has been end-of-life since September 2019. No security patches or bug fixes are available. Recommended upgrade targets:
Run jdeps –jdk-internals against your Java 12 application to identify dependencies on encapsulated APIs before upgrading.
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