The GNU Trove library has two objectives:

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.

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.