fastutil extends the Java Collections Framework by providing type-specific
maps, sets, lists and priority queues with a small memory footprint and
fast access and insertion; it also includes a fast I/O API for binary and
text files. The classes implement their standard counterpart interface
(e.g., Map for maps) and can be plugged into existing code. Moreover, they
provide additional features (such as bidirectional iterators) that are not
available in the standard classes.