A suite of classes that extend or augment the Java Collections Framework.

Commons-Collections seek to build upon the JDK classes by providing new interfaces, implementations and utilities. There are many features,
including:

Special-purpose implementations of Lists and Maps for fast access Adapter
classes from Java1-style containers (arrays, enumerations) to Java 2-style
collections. Methods to test or create typical set-theory properties of
collections such as union, intersection, and closure.

WWW: http://commons.apache.org/proper/commons-collections/
