The development repositories are open for bug fixes, small enhancements, and JEPs as proposed and tracked via the JEP Process.
What Is JEP?
This JEP is the index of all JDK Enhancement Proposals, known as JEPs. JDK 12 is the open-source reference implementation of version 12 of the Java SE Platform as specified by by JSR 386 in the Java Community Process.
The List of Added Features:-
1. JEP 189 - A Low-Pause-Time Garbage Collector
2. JEP 325 - Switch Expressions
3. JEP 326 - Raw String Literals is dropped from JDK 12 release
4. JEP 230 - Microbenchmark Suite
5. JEP 334 - JVM Constants API
6. JEP 340 - One AArch64 Port, Not Two
7. JEP 341 - Default CDS Archives
8. JEP 344 - Abortable Mixed Collections for G1
9. JEP 346 - Promptly Return Unused Committed Memory from G1
Source for detail - https://metebalci.com/blog/what-is-new-in-java-12/