### Question:
HistogramDataset extends AbstractIntervalXYDataset implements IntervalXYDataset, Cloneable, PublicCloneable,
                   Serializable { @Override public Comparable getSeriesKey(int series) { Map<String, Object> map = this.list.get(series); return (Comparable) map.get("key"); } HistogramDataset(); HistogramType getType(); void setType(HistogramType type); void addSeries(Comparable key, double[] values, int bins); void addSeries(Comparable key, double[] values, int bins,
            double minimum, double maximum); @Override int getSeriesCount(); @Override Comparable getSeriesKey(int series); @Override int getItemCount(int series); @Override Number getX(int series, int item); @Override Number getY(int series, int item); @Override Number getStartX(int series, int item); @Override Number getEndX(int series, int item); @Override Number getStartY(int series, int item); @Override Number getEndY(int series, int item); @Override boolean equals(Object obj); @Override Object clone();  }### Answer:
@Test public void testGetSeriesKey() { double[] values = {1.0, 2.0, 3.0, 4.0, 6.0, 12.0, 5.0, 6.3, 4.5}; HistogramDataset d1 = new HistogramDataset(); d1.addSeries("Series 1", values, 5); assertEquals("Series 1", d1.getSeriesKey(0)); }