1.深度拷贝，使用clone()方法。
4.2.2 LocalDate Class
使用工厂方法创建对象
LocalDate now=LocalDate.now();
LOcalDate new YearsEve=LocalDate.of(1999,12,31)
;
调用方法获得年月日
int year=newYearsEve.getYear();
int month=newYearsEve.getMonthValue();
int year=newYearsEve.getDayOfMonth();
LocalDate aThousandDaysLater=newYearEve.plusDays(1000);
year=aThousandDaysLater.getYear();
