The Google Collections Library 1.0 is a set of new collection types, implementations and related goodness for Java 5 and higher, brought to you by Google. It is a natural extension of the Java Collections Framework.

We have finally (Dec 30, 2009) released version 1.0-final! The API is now frozen: there will be no more source- or binary-incompatible changes, except those that can be performed via a minimum 18-month-long deprecation window. However, we reserve the right to make alterations to the serialized form of these objects, so do not depend on this form remaining stable.

Download Google Collections Library 1.0-final now

Note about Guava

We have created a project called Guava to house a plethora of important core libraries for Java. In the near future, that project will include the Google Collections Library, and the project you're looking at now will cease to exist as its own independent entity. We apologize in advance for confusion this will certainly cause.

What's in here?

• New Collection types: Multimap, Multiset, BiMap and others
• High-performance immutable implementations of the standard collection types, for example ImmutableSet
• MapMaker, a builder for concurrent hash maps with many advanced features
• Ordering, which can only be described as a "Comparator on steroids"
• Iterators and Iterables utility classes: element-based equality, cycle, concat, partition, filter with predicate, transform with function, and much more
• Lists, Sets and Maps utility classes: a plethora of convenient factory methods and much more
• Forwarding collections, such as ForwardingSet, allowing you to customize collection behavior without subclassing
• Implementation helpers like AbstractIterator
• and still more

This piece of art is worth looking into. It's Josh Bloch's vision and includes all the latest tips and tricks related to Generics and Data Structures.