@PreviewFeature
.
A preview feature is a new feature of the Java language, Java Virtual Machine, or Java SE API that is fully specified, fully implemented, and yet impermanent. The notion of a preview feature is defined in JEP 12.
If a code depends on a preview feature it might stop compiling in the future JDK versions if the feature get no positive feedback and, hence, it either gets removed or changed.
It's enabled only if the language level of the current project is a preview one.
New in 2021.1