code: public <T> TableFormatter header(Collection<? extends T> collection) {
        header.addAll(collection);
        longestCell = (int) Math.max(longestCell, collection.stream()
                                                            .mapToDouble(o -> o.toString().length() + 2)
                                                            .max()
                                                            .orElse(0));
        return this;
     }
docs: Header table formatter.
  
  @param collection the collection
  @return the table formatter