[28] JEP 539: Strict Field Initialization in the JVM (Preview)

ref: https://openjdk.org/jeps/539

Summary
Introduce strictly-initialized fields in the Java Virtual Machine. Such fields must be initialized before they are read, thus default values such as 0 or null are never observed. For strictly-initialized fields that are final, the same value is always observed. This is a [preview VM feature](https://openjdk.org/jeps/12), available for use by compilers that emit class files.