It is the framework of lazy collections based on Iterator and Iterable interfaces
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.
Trove of primitive collections with Apache 2.0 license, built for Java Java 6 or 7
Trove of primitive collections with Apache 2.0 license, built for Java Java 8
Custom Collection Implementations
In-memory, bounded-size queue data structure that aims at minimizing garbage collection overhead (especially latency)