public @interface Private
A class that is considered private to the internals of Spark -- there is a high-likelihood
they will be changed in future versions of Spark.
This should be used only when the standard Scala / Java means of protecting classes are
insufficient. In particular, Java has no equivalent of private[spark], so we use this annotation
in its place.
NOTE: If there exists a Scaladoc comment that immediately precedes this annotation, the first
line of the comment must be ":: Private ::" with no trailing blank line. This is because
of the known issue that Scaladoc displays only either the annotation or the comment, whichever