code: private void enlargeOffset() {
  	if (offset == 0) {
  	    offCount = offCount == 0 ? 1 : offCount * 2;
  	    offset = offCount;
  	    Object[] narr = new Object[arr.length + offset];
  	    for (int i = 0; i < size; i++) {
  		narr[offset + i] = arr[i];
  	    }
  	    arr = narr;
  	}
      }
docs: !!! all methods that use this method must be sync enlarge the offset if 0