计算两个日期之间的天数

//计算两个日期之间的天数
public class CalendarTest {
    public static void main(String[] args) {
        Calendar instance = Calendar.getInstance();
        instance.set(2010, 9, 7);
        //以毫秒为单位返回此日历的时间值
        long d1 = instance.getTimeInMillis();
        instance.set(2020, 9, 7);
        long d2 = instance.getTimeInMillis();
        //1秒=1000毫秒
        long days = (d2 - d1) / (1000 * 60 * 60 * 24);
        System.out.println(days);
    }
}