Open Source Collections Libraries in Java

Extends the JDK with new interfaces and implementations: Bag, Buffer, BidiMap, MapIterator, ordered maps/sets, type-checking and transforming decorators, composite collections, reference map, comparators and iterators, set-theory utilities.

Extends the Java Collections Framework with type-specific maps, sets, lists and queues; small memory footprint and fast access. Big arrays and 64-bit indices; binary and text I/O utilities. Apache 2.

Suite of new collection types and utilities for Java: BiMap, Multiset, Multimap (SetMultimap, ListMultimap), immutable collections, graph library, and concurrency and I/O helpers. Now developed as Guava.

Fast, lightweight implementations of the java. util Collections API as pluggable replacements for JDK equivalents. Primitive collections (int, long, etc.

High-performance adaptive histogram for Java: accepts large datasets with any distribution, small memory footprint, no pre- or post-processing. Cumulative density and percentile statistics.

Java library of iterators, algorithms and functions inspired by the C++ STL: transform, chain, zip, tee; functional-style composition over collections.

Collections and utilities for Java primitive types (boolean, byte, char, double, float, int, long, short). Smaller and faster than Object-based alternatives; avoids auto-boxing overhead.

Collection classes for primitive types (int, boolean, double, etc. ) as an efficient alternative to the JCF. Symmetrical interface hierarchy per primitive; JCF adapters; specialized implementations and benchmarks.

Free graph library for Java under LGPL; commercial use allowed. Provides graph data structures and algorithms.

Type-specific collections library for Java; framework for collections keyed or valued by primitive or specific types.