code: private static MessageBuffer newMessageBuffer(byte[] arr, int off, int len)
      {
          checkNotNull(arr);
          if (mbArrConstructor != null) {
              return newInstance(mbArrConstructor, arr, off, len);
          }
          return new MessageBuffer(arr, off, len);
      }
docs: Creates a new MessageBuffer instance backed by a java heap array
  
  @param arr
  @return