Simian (http://www.redhillconsulting.com.au/products/simian) identifies duplicated (copy and pasted) lines in Java source code.

Especially on large J2EE projects, it can be difficult for any one developer to keep track of all the features (classes, methods, etc.) of the system.

Simian is extremely fast. Modestly sized projects (20,000 to 50,000 lines of code) can take a few seconds. Running against the entire JDK 1.4.1_02 source base (488,169 lines of code in 2794 files) in under 50 seconds (on a P4 1.8GHz machine) identified 50,354 duplicate lines in 826 files!

Multiple execution methods:

Checkstyle plugin
Ant task
Command line interface
Runs under Java2 1.3 or higher.

Simian is available with licensing specific for either free or commercial use depending on your project.

Free evaluation version also available: http://www.redhillconsulting.com.au/products/simian/simian.zip