JAVA计算两日期之间相差的天数

public class BetweenOfToday {
    
    public static void main(String[] args) {

        Calendar cal3 = Calendar.getInstance();
        TimeToZero(cal3);//时间都归为0点，保证差值准确
        cal3.set(2022,3,20);//4月20号，因为月份0-11
        long t3 = cal3.getTime().getTime();//先用getTime转成Date对象，再获取毫秒数

        Calendar cal4 = Calendar.getInstance();
        TimeToZero(cal4);
        cal4.set(2022,3,24);
        long t4 = cal4.getTime().getTime();

        long day_between = (t4-t3)/1000/3600/24;//毫秒数之差除以1000，再除以60秒，再除以60分钟，再除以24小时
        System.out.println(day_between);
    }
    
    public static void TimeToZero(Calendar cal){
        cal.set(Calendar.HOUR_OF_DAY,0);
        cal.set(Calendar.MINUTE,0);
        cal.set(Calendar.SECOND,0);
        cal.set(Calendar.MILLISECOND,0);
    }
}