What is "java-12"

The Java 12 was released on March 19, 2019.

Below are the Features included in this version, in addition to the respective number of JEP:

• 189: Shenandoah: A Low-Pause-Time Garbage Collector (Experimental)
• 230: Microbenchmark Suite
• 325: Switch Expressions (Preview)
• 334: JVM Constants API
• 340: One Aarch64 Port, Not Two
• 341: Default CDS Archives
• 344: Abortable Mixed Collections for G1
• 346: Promptly Return Unused Committed Memory from G1

See also the Release Notes on the Oracle website.