We present the design and implementation of Tax- TOOLJ, Taxonomy Tool for Object-Oriented Language Java TaxTOOLJ is a reverse engineering tool that catalogs the classes of a Java software application using the taxonomy of object oriented classes TaxTOOLJ is entirely implemented in Java, which makes it very reliable, portable, and maintainable It represents a scalable tool that performs efficiently during introspection of large scale Java applications and enables support for program understanding, software metrics, testing, reengineering and reuse of the systems.