GNU Trove: High performance collections for Java.

The GNU Trove library has two objectives:

   1. Provide "free" (as in "free speech" and "free beer"), fast,
   lightweight implementations of the java.util Collections API.
   These implementations are designed to be pluggable replacements
   for their JDK equivalents.
   
   2. Whenever possible, provide the same collections support for
   primitive types. This gap in the JDK is often addressed by using
   the "wrapper" classes (java.lang.Integer, java.lang.Float, etc.)
   with Object-based collections. For most applications, however,
   collections which store primitives directly will require less
   space and yield significant performance gains. 

WWW: http://trove4j.sourceforge.net/