code: void setGeometryUserIndex(int geom, int index, int value) {
  		AttributeStreamOfInt32 stream = m_geometry_indices.get(index);
  		int pindex = getGeometryIndex_(geom);
  		if (pindex >= stream.size())
  			stream.resize(Math.max((int) (pindex * 1.25), (int) 16), -1);
  		stream.write(pindex, value);
  	}
docs: Sets value to the given user index on a geometry.