Java实现两个日期相减等于天数

      // 定义项目进行天数
      long Days = 0;
      SimpleDateFormat sdf = new SimpleDateFormat("yyyy-MM-dd");
      try {
          long time = sdf.parse("2021-01-19").getTime();
          long time1 = sdf.parse("2020-10-12")
              .getTime();
          Days = (int) ((time -time1) /(24
                        * 60 * 60 * 1000));
              } catch (ParseException e) {
          e.printStackTrace();
        }

import java.text.ParseException;
import java.text.SimpleDateFormat;
import java.time.LocalDateTime;
import java.util.Calendar;
public class TestDay {
    public static void main(String[] args) {
        String dateStr1 = "2020-09-30";
        String dateStr2 = "2021-01-12";
        SimpleDateFormat sdf = new SimpleDateFormat("yyyyMMdd");
        SimpleDateFormat sdf2 = new SimpleDateFormat("yyyy-MM-dd");
        try {
            dateStr1 = sdf.format(sdf2.parse(dateStr1));
            dateStr2 = sdf.format(sdf2.parse(dateStr2));
        } catch (ParseException e) {
            e.printStackTrace();
        }
        long time1 = time(dateStr1);
        long time2 = time(dateStr2);
        // 相减得出的天数mills
        long mills = time1> time2
                ? time1 - time2
                        : time2 - time1;
        System.out.println((int) (mills / 1000 / 3600 / 24));
    }
    // 封装截取字符串
    public  static long time(String times){
        int year = Integer.parseInt(times.substring(0, 4));
        int month = Integer.parseInt(times.substring(4, 6));
        int day = Integer.parseInt(times.substring(6, 8));
        Calendar c = Calendar.getInstance();
        c.set(Calendar.YEAR, year);
        c.set(Calendar.MONTH, month - 1);
        c.set(Calendar.DAY_OF_MONTH, day);
        return (c.getTimeInMillis());
    }
}

      SimpleDateFormat sdf = new SimpleDateFormat("yyyy-MM-dd");
      // 自己定义yyyy-mm-dd ,mm小写，导致出现负数的情况，M与m的区别 区分 月和分,如：yyyy-MM-dd HH:mm:ss;
      SimpleDateFormat sdf = new SimpleDateFormat("yyyy-mm-dd");