### Question:
Month extends RegularTimePeriod implements Serializable { @Override public long getSerialIndex() { return this.year * 12L + this.month; } Month();  Month(int month, int year);  Month(int month, Year year);  Month(Date time);  Month(Date time, TimeZone zone, Locale locale); Year getYear(); int getYearValue(); int getMonth(); @Override long getFirstMillisecond(); @Override long getLastMillisecond(); @Override void peg(Calendar calendar); @Override RegularTimePeriod previous(); @Override RegularTimePeriod next(); @Override long getSerialIndex(); @Override String toString(); @Override boolean equals(Object obj); @Override int hashCode(); @Override int compareTo(TimePeriod o1); @Override long getFirstMillisecond(Calendar calendar); @Override long getLastMillisecond(Calendar calendar); static Month parseMonth(String s);  }### Answer:
@Test public void testGetSerialIndex() { Month m = new Month(1, 2000); assertEquals(24001L, m.getSerialIndex()); m = new Month(1, 1900); assertEquals(22801L, m.getSerialIndex()); }