### Question:
XYSeries extends Series implements Cloneable, Serializable { @Override public boolean equals(Object obj) { if (obj == this) { return true; } if (!(obj instanceof XYSeries)) { return false; } if (!super.equals(obj)) { return false; } XYSeries that = (XYSeries) obj; if (this.maximumItemCount != that.maximumItemCount) { return false; } if (this.autoSort != that.autoSort) { return false; } if (this.allowDuplicateXValues != that.allowDuplicateXValues) { return false; } if (!ObjectUtilities.equal(this.data, that.data)) { return false; } return true; } XYSeries(Comparable key);  XYSeries(Comparable key, boolean autoSort);  XYSeries(Comparable key, boolean autoSort,
            boolean allowDuplicateXValues); double getMinX(); double getMaxX(); double getMinY(); double getMaxY(); boolean getAutoSort(); boolean getAllowDuplicateXValues(); @Override int getItemCount(); List<XYDataItem> getItems(); int getMaximumItemCount(); void setMaximumItemCount(int maximum); void add(XYDataItem item); void add(double x, double y); void add(double x, double y, boolean notify); void add(double x, Number y); void add(double x, Number y, boolean notify); void add(Number x, Number y); void add(Number x, Number y, boolean notify); void add(XYDataItem item, boolean notify); void delete(int start, int end); XYDataItem remove(int index); XYDataItem remove(Number x); void clear(); XYDataItem getDataItem(int index); Number getX(int index); Number getY(int index); void updateByIndex(int index, Number y); void update(Number x, Number y); XYDataItem addOrUpdate(double x, double y); XYDataItem addOrUpdate(Number x, Number y); XYDataItem addOrUpdate(XYDataItem item); int indexOf(Number x); double[][] toArray(); @Override Object clone(); XYSeries createCopy(int start, int end); @Override boolean equals(Object obj); @Override int hashCode();  }### Answer:
@Test public void testEquals() { XYSeries s1 = new XYSeries("Series"); s1.add(1.0, 1.1); XYSeries s2 = new XYSeries("Series"); s2.add(1.0, 1.1); assertEquals(s1, s2); assertEquals(s2, s1); s1.setKey("Series X"); assertFalse(s1.equals(s2)); s2.setKey("Series X"); assertEquals(s1, s2); s1.add(2.0, 2.2); assertFalse(s1.equals(s2)); s2.add(2.0, 2.2); assertEquals(s1, s2); }