Guava is a suite of core and expanded libraries that include utility classes, google's collections, io classes, and much much more.
Functional extension of google collections
Trove of primitive collections with Apache 2.0 license, built for Java Java 8
Collections and utilities based on primitives types
Trove of primitive collections with Apache 2.0 license, built for Java Java 6 or 7
Java Common Library Collections Multimap
Library providing immutable/persistent collection classes for Java. While collections are immutable they provide methods for adding and removing values by creating new modified copies of themselves. Each copy shares almost all of its structure with other copies to minimize memory consumption.
In-memory, bounded-size queue data structure that aims at minimizing garbage collection overhead (especially latency)
It is the framework of lazy collections based on Iterator and Iterable interfaces