Home – Apache Commons Collections
Apache Commons Collections ™
Last Published: 19 Apr 2025
Version: 4.5.0
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Commons Collections
The
Java Collections Framework
was a major addition in Java 1.2.
It added many powerful data structures that accelerate development of most significant Java applications.
Since that time it has become the recognised standard for collection handling in Java.
Commons-Collections seek to build upon the JDK classes by providing new interfaces, implementations and utilities.
There are many features, including:
Bag interface for collections that have a number of copies of each object
BidiMap interface for maps that can be looked up from value to key as well and key to value
Bloom filter
classes and interfaces
MapIterator interface to provide simple and quick iteration over maps
Transforming decorators that alter each object as it is added to the collection
Composite collections that make multiple collections look like one
Ordered maps and sets that retain the order elements are added in, including an LRU based map
Reference map that allows keys and/or values to be garbage collected under close control
Many comparator implementations
Many iterator implementations
Adapter classes from array and enumerations to collections
Utilities to test or create typical set-theory properties of collections such as union, intersection, and closure
Documentation
A getting started
User's Guide
is available
as are various
project reports
The Javadoc API documents are available online:
The
current release
The latest 3.x release -
version 3.2.2
The latest 2.x release -
version 2.1.1
The
source repository
can be
browsed
, and we have a mirror
on
GitHub
Releases
The latest version is available:
Download now!
This requires Java 8 or later, see also the
release notes
For previous releases, see the
Apache Archive
Support
The
commons mailing lists
act as the main support forum.
The user list is suitable for most library usage queries.
The dev list is intended for the development discussion.
Please remember that the lists are shared between all commons components,
so prefix your email by [collections].
Issues may be reported via
ASF JIRA
Please read the instructions carefully to submit a useful bug report or enhancement request.
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The Apache Software Foundation