code: public static String join(List<?> things, String delim) {
          StringBuilder builder = new StringBuilder();
          boolean first = true;
          for (Object thing : things) {
              if (first) {
                  first = false;
              } else {
                  builder.append(delim);
              }
              builder.append(thing.toString());
          }
          return builder.toString();
      }
docs: Returns a list joined together by the provided delimiter, for example,
  ["a", "b", "c"] could be joined into "a,b,c"
  
  @param things the things to join together
  @param delim  the delimiter to use
  @return a string contained the things joined together