code: public static FastStr of(Collection<Character> col) {
          int sz = col.size();
          if (0 == sz) return EMPTY_STR;
          char[] buf = new char[sz];
          Iterator<Character> itr = col.iterator();
          int i = 0;
          while (itr.hasNext()) {
              buf[i++] = itr.next();
          }
          return new FastStr(buf, 0, sz);
      }
docs: Construct a FastStr instance from a collection of characters
  @param col the character collection
  @return a FastStr instance