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

There are certain holes left unfilled by Sun's implementations, and the
Jakarta-Commons Collections Component strives to fulfill them. Among the
features of this package are: 

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://jakarta.apache.org/commons/collections/