Parse CSV using database and fieldFilter parameters

Question

I created a method using an ArrayList that is building a list from a CSV File. I am having trouble adding the String value of the field to the list. When I tried to use field.add() it gives me an error "The method add(String) is undefined for the type String". How do I fix this and make it so I can add the String value to the list and return the ArrayList?

 /**
   * This method begins by creating a new ArrayList of Strings. It then 
   *     attaches a Scanner to the provided File object and uses a while
   *     loop to process the file line-by-line. For each line, this method creates
   *     a new Scanner object with a comma "," delimiter to to enable access the
   *     individual fields within the line using a second, inner while loop. As each
   *     field is processed it is tracked using a counter variable starting with
   *     field 1. If the current field is equal to the specified fieldFilter, the
   *     String value of the field is added to the list.  Once all the lines in the 
   *     file have been processed, the ArrayList is returned to the caller.
   * 
   * If Scanner throws a FileNotFoundException when instantiating the new file 
   *     Scanner object, catch the expection, display an error message, and exit 
   *     the program immediately with an exit status of 1.
   * 
   * @param csvFile File object that contains the CSV database to process
   * @param fieldFilter Field number to use for building the list
   * @return ArrayList of strings that represents the desired column of data from the database.
   */
  public static ArrayList<String> buildListFromCSV(File database, int fieldFilter) {
    final int ERROR_CODE = 1;

    try {
        Scanner fileScanner = new Scanner(database);

        while (fileScanner.hasNextLine()) {
          String line = fileScanner.nextLine();

          Scanner lineScanner = new Scanner(line);
          lineScanner.useDelimiter(",");

          int fieldCounter = 1;
          while (lineScanner.hasNext()) {
            String field = lineScanner.next();
            if (fieldCounter == fieldFilter) {
              field.add();
            }
            fieldCounter++;
          }
          lineScanner.close();
        }
        fileScanner.close();
      } catch (FileNotFoundException e) {
        System.out.println("Unable to open file: " + database);
                System.exit(ERROR_CODE);
      }
      return field;
    }