PMD scans Java source code and looks for potential problems like:

    * Possible bugs - empty try/catch/finally/switch statements
    * Dead code - unused local variables, parameters and private methods
    * Suboptimal code - wasteful String/StringBuffer usage
    * Overcomplicated expressions - unnecessary if statements, for loops 
      that could be while loops
    * Duplicate code - copied/pasted code means copied/pasted bugs

WWW: http://pmd.sourceforge.net/