http://fastutil.di.unimi.it/: 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; provides also big (64-bit) arrays, sets and lists, sorting algorithms, and fast, practical I/O classes for binary and text files.
  • Sebastiano Vigna 
Type-specific classes for integer elements or keys.

/**
 * Type-specific classes for integer elements or keys.
 */
package it.unimi.dsi.fastutil.ints;