Signifies that a public API (public class, method or field) is subject to
incompatible changes, or even removal, in a future release. An API bearing
this annotation is exempt from any compatibility guarantees made by its
containing library. Note that the presence of this annotation implies nothing
about the quality or performance of the API in question, only the fact that
it is not "API-frozen."
It is generally safe for applications to depend on beta APIs, at
the cost of some extra work during upgrades. However it is generally
inadvisable for libraries (which get included on users' CLASSPATHs,
outside the library developers' control) to do so.