code: public void openListing(File listingFile) {
          if (listingFile != null) {
              try {
                  listing = new PrintWriter(new FileWriter(listingFile));
              } catch (IOException e) {
                  error(listingFile.getName(), "can't open listing file - listing disabled");
                  listing = null;
              }
          } else {
              listing = null;
          }
      }
docs: -- listing