Extends the the Java™ Collections Framework by providing type-specific maps, sets, lists and priority queues with a small memory footprint and fast access and insertion; provides also big (64-bit) arrays, sets and lists, and fast, practical I/O classes for binary and text files.

See: Description

Packages 
Package Description
it.unimi.dsi.fastutil  
it.unimi.dsi.fastutil.booleans
Provides type-specific classes for boolean elements or keys.
it.unimi.dsi.fastutil.bytes
Provides type-specific classes for byte elements or keys.
it.unimi.dsi.fastutil.chars
Provides type-specific classes for character elements or keys.
it.unimi.dsi.fastutil.doubles
Provides type-specific classes for double elements or keys.
it.unimi.dsi.fastutil.floats
Provides type-specific classes for float elements or keys.
it.unimi.dsi.fastutil.ints
Provides type-specific classes for integer elements or keys.
it.unimi.dsi.fastutil.io
Provides classes and static methods that make object and primitive-type I/O easier and faster.
it.unimi.dsi.fastutil.longs
Provides type-specific classes for long elements or keys.
it.unimi.dsi.fastutil.objects
Provides type-specific classes for object elements or keys.
it.unimi.dsi.fastutil.shorts
Provides type-specific classes for short elements or keys.