fastutil extends the Java Collections Framework by providing type-specific maps, sets, lists, and queues with a small memory footprint and fast access and insertion; it provides also big (64-bit) arrays, sets and lists, sorting algorithms, fast, ...

Types that extend and augment the Java Collections Framework.

Java implementation of a concurrent trie hash map from Scala collections library

The Apache Commons Collections package contains types that extend and augment the Java Collections Framework.

Highly Scalable Java

feature-rich collections framework for Java, offering alternatives to standard Java Collections.

The API module of Eclipse Collections, offering rich and efficient data structures for Java.

The Trove library provides high speed regular and primitive collections for Java.

Google Collections Library is a suite of new collections and collection-related goodness for Java 5.0

MapDB provides concurrent Maps, Sets and Queues backed by disk storage or off-heap memory. It is a fast, scalable and easy to use embedded Java database.