code: public String join(List<?> list, String separator) {
          int size = list.size();
          StringBuilder buffer = new StringBuilder(512);
          for (int i = 0; i < size; i++) {
              Object item = list.get(i);
              if (i > 0) { buffer.append(separator); }
              buffer.append(item.toString());
          }
          
          return buffer.toString();
      }
docs: Join the contents of the given list separated by the given separator.
  For example, the list [a, b, c] with separator ' ' would result in:
  <code>a b c</code>.
  
  @param list  The list to join
  @param separator The separator between values
  
  @return The resulting string