java - 为什么 GregorianCalendar.getTimeInMillis() 和 GregorianCalendargetTimeInMillis(1970.01.01) 之间存在差异

Question

我尝试将出生日期和当前日期进行比较 然后我试图了解年龄。 但当前日期函数以给定日期之外的另一个日期开始 我的代码:

GregorianCalendar birthdate = new GregorianCalendar(2001,06,20);
long ms = System.currentTimeMillis() - birthdate.getTimeInMillis();
double years = (((double)ms / 1000)/31536000) ;
System.out.print(years);
// years Shoud be 18 here but it returns 17.3
if (years > 18) {
  // Code Block
}
else{
  System.out.print("to Jung");
}

Answer 1

检查Constructor on GregorianCalendar.

public GregorianCalendar(int year, int month, int dayOfMonth)

Constructs a GregorianCalendar with the given date set in the default time zone with the default locale.

year - the value used to set the YEAR calendar field in the calendar.

month - the value used to set the MONTH calendar field in the calendar. Month value is 0-based. e.g., 0 for January.

dayOfMonth - the value used to set the DAY_OF_MONTH calendar field in the calendar.

您正在创建 7 月 20 日的日期，该日期恰好偏移了一个月，即大约 0.08 年。