The following were some of the important additions and updates in Java SE 12 and JDK 12:

• JVM Constants API was introduced to model nominal descriptions of key class-file and run-time artifacts, in particular constants that were loadable from the constant pool. See JVM Constant API.
• The switch statement was extended so that it can be used either as a statement or an expression. This is a preview language feature. See JEP 325: Switch Expressions (Preview) and JEP 12: Preview Language and VM Features.
• Support for Unicode 11.0. See Unicode 11.0.
• Square character support was provided for the Japanese Reiwa Era, which began on May, 2019. See Square character support.
• The NumberFormat added support for formatting a number in its compact form. See Compact Number Formatting Support .