code: private void walkDir(File dir) {
          walkDir(
                  dir,
                  new FileFilter() {
                      @Override
                      public boolean accept(File pathname) {
                          return ( pathname.isFile() && pathname.getName().endsWith( ".class" ) );
                      }
                  },
                  new FileFilter() {
                      @Override
                      public boolean accept(File pathname) {
                          return ( pathname.isDirectory() );
                      }
                  }
          );
      }
docs: Expects a directory.