In Java, there are only two categories of … always values of primitive types such as int; … of objects. Guava … extends the non-references to include user-defined classes [i.e., values] … [and] it partitions the references into [shared monitors and unshared objects]. … [Guava values may be mutable], but they are never shareable. … Values, monitors, and objects form disjoint class hierarchies. …
Google-1
Google-2
Copyright clearance needed for quotation.