The Java Memory Model - Java Concurrency in Practice - page 407

Initialization safety makes visibility guarantees only for the values that are reachable through
final fields as of the time the constructor finishes. For values reachable through nonfinal
fields, or values that may change after construction, you must use synchronization to ensure
visibility.
Summary
The Java Memory Model specifies when the actions of one thread on memory are guaranteed
to be visible to another. The specifics involve ensuring that operations are ordered by a partial
ordering called happens-before , which is specified at the level of individual memory and
synchronization operations. In the absence of sufficient synchronization, some very strange
things can happen when threads access shared data. However, the higher-level rules offered
in Chapters 2 and 3 , such as @GuardedBy and safe publication, can be used to ensure thread
safety without resorting to the low-level details of happens-before .