The introduction of the Collections API by Sun in JDK 1.2
has been a boon to quick and effective Java programming.
Ready access to powerful data structures has accelerated
development by reducing the need for custom container
classes around each core object. Most Java2 APIs are
significantly easier to use because of the Collections API.
However, 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 Java2-style collections

- methods to test or create typical set theory properties
of collections such as union, intersection, and closure