google-collections

The Google Collections Library is a suite of new collections and collection-related goodness for Java 5.0. This library is a natural extension of the Java Collections Framework. The major new types are: * BiMap. A Map that guarantees unique values, and supports an inverse view. * Multiset. A Collection that may contain duplicate values like a List, yet has order-independent equality like a Set. Often used to represent a histogram. * Multimap. Similar to Map, but may contain duplicate keys. Has subtypes SetMultimap and ListMultimap providing more specific behavior.