code: public StringBuffer format(Object pat, StringBuffer result, FieldPosition fpos) {
          String pattern = processPattern((String) pat);
          int lastOffset = 0;
  
          for (int i = 0; i <= maxOffset; ++i) {
              int offidx = offsets[i];
              result.append(pattern.substring(lastOffset, offsets[i]));
              lastOffset = offidx;
  
              String key = arguments[i];
              String obj;
              if (key.length() > 0) {
                  obj = formatObject(processKey(key));
              } else {
                  // else just copy the left and right braces
                  result.append(this.ldel);
                  result.append(this.rdel);
                  continue;
              }
  
              if (obj == null) {
                  // try less-greedy match; useful for e.g. PROP___PROPNAME__ where
                  // 'PROPNAME' is a key and delims are both '__'
                  // this does not solve all possible cases, surely, but it should catch
                  // the most common ones
                  String lessgreedy = ldel + key;
                  int fromright = lessgreedy.lastIndexOf(ldel);
  
                  if (fromright > 0) {
                      String newkey = lessgreedy.substring(fromright + ldel.length());
                      String newsubst = formatObject(processKey(newkey));
  
                      if (newsubst != null) {
                          obj = lessgreedy.substring(0, fromright) + newsubst;
                      }
                  }
              }
  
              if (obj == null) {
                  if (throwex) {
                      throw new IllegalArgumentException("ObjectForKey");
                  } else {
                      obj = ldel + key + rdel;
                  }
              }
  
              result.append(obj);
          }
  
          result.append(pattern.substring(lastOffset, pattern.length()));
  
          return result;
      }
docs: Formats the parsed string by inserting table's values.
  
  @param pat    a string pattern
  @param result Buffer to be used for result.
  @param fpos   position
  @return Formatted string