XYSeriesCollection data = new XYSeriesCollection(); XYSeries series = new XYSeries("Test"); data.addSeries(series); series.add(1, 42); System.out.println(data.getSeries(0).getY(0)); XYSeriesCollection dataCopy = (XYSeriesCollection) data.clone(); series.updateByIndex(0, 21.0); System.out.println(data.getSeries(0).getY(0)); System.out.println(dataCopy.getSeries(0).getY(0));