code: public void add(KType e1, KType e2) {
      ensureBufferSpace(2);
      buffer[elementsCount++] = e1;
      buffer[elementsCount++] = e2;
    }
docs: Appends two elements at the end of the list. To add more than two elements,
  use <code>add</code> (vararg-version) or access the buffer directly (tight
  loop).