PMD is a Java source code analyzer - it finds unused variables, questionable design decisions, empty catch blocks, and so forth. You can read much more about PMD here - http://pmd.sf.net/.
There's a new 'PMD' menu item in the Plugins menu. This checks your currently displayed Java code and puts the results in the ErrorList.
There's also a new section in the Global Options configuration panel that lets you pick rule sets.
The PMD-JEdit plugin is free software released under the Apache license.