### Question:
XIntervalSeries extends ComparableObjectSeries { public double getXHighValue(int index) { XIntervalDataItem item = (XIntervalDataItem) getDataItem(index); return item.getXHighValue(); } XIntervalSeries(Comparable key);  XIntervalSeries(Comparable key, boolean autoSort,
            boolean allowDuplicateXValues); void add(double x, double xLow, double xHigh, double y); Number getX(int index); double getXLowValue(int index); double getXHighValue(int index); double getYValue(int index); @Override ComparableObjectItem getDataItem(int index);  }### Answer:
@Test public void testGetXHighValue() { XIntervalSeries s1 = new XIntervalSeries("S1"); s1.add(1.0, 2.0, 3.0, 4.0); assertEquals(3.0, s1.getXHighValue(0), EPSILON); s1.add(2.0, 1.0, 4.0, 2.5); assertEquals(4.0, s1.getXHighValue(1), EPSILON); }