方法1：long值相减（推荐）

public static void main(String[] args) {DateFormat dateFormat = new SimpleDateFormat("yyyy-MM-dd HH:mm:ss");try {Date startDate = dateFormat.parse("2024-03-01 10:00:00");//开始时间Date endDate = dateFormat.parse("2024-03-02 14:00:00");//结束时间long msNum = endDate.getTime()-startDate.getTime();//时间戳相差的毫秒数long dayNum = msNum/(24*60*60*1000)//除以一天的毫秒数，得到相差天数System.out.println("相差天数为："+ dayNum);} catch (ParseException e) {e.printStackTrace();}
}

方法2：

public static void main(String[] args) {DateFormat dft = new SimpleDateFormat("yyyy-MM-dd");try {Date star = dft.parse("2020-02-03");//开始时间Date endDay=dft.parse("2025-03-02");//结束时间Date nextDay=star;int i=0;while(nextDay.before(endDay)){//当明天不在结束时间之前是终止循环Calendar cld = Calendar.getInstance();cld.setTime(star);cld.add(Calendar.DATE, 1);star = cld.getTime();//获得下一天日期字符串nextDay = star; i++;}System.out.println("相差天数为："+i);} catch (ParseException e) {e.printStackTrace();}}

方法3：

public static void main(String[] args) {String star="2020-02-03";String end="2025-03-02";String[] star1=star.split("-");String[] end1=end.split("-");int days=0;if(Integer.parseInt(star1[0])<Integer.parseInt(end1[0])){for(int i=Integer.parseInt(star1[0]);i<Integer.parseInt(end1[0]);i++){//计算是否是瑞年if(i%4==0&&i%100!=0||i%400==0){days+=366;}else{days+=365;}}}//得到开始那一年已过去的日期int starday=days(star1[0],star1[1],star1[2]);//得到结束那一年已过去的日期int endday=days(end1[0],end1[1],end1[2]);//减去开始那一年已过去的日期，加上结束那一年已过去的日期days=days-starday+endday;System.out.println("相差的天数："+days);}public static int days(String year,String month,String day){int days=0;int nowyear=Integer.parseInt(year);int[] monthday={0,31,28,31,30,31,30,31,31,30,31,30,31};int[] monthday1={0,31,29,31,30,31,30,31,31,30,31,30,31};boolean flag=true;if(nowyear%4==0&&nowyear%100!=0||nowyear%400==0){}else{flag=false;}for(int i=0;i<Integer.parseInt(month);i++){if(flag){days+=monthday1[i];}else{days+=monthday[i];}}days+=Integer.parseInt(day);return days;}

方法4：

int y;int m;int d;public test2(int y,int m,int d ){this.y=y;this.m=m;this.d=d;}public int sum(test2 d){int day=0;int[] x={0,31,28,31,30,31,30,31,31,30,31,30,31};for(int i=1;i<d.y;i++){if(i%4==0&& i%100!=0 || i%400==0){day+=366;}else{day+=365;}}if(d.y%4==0&& d.y%100!=0 || d.y%400==0){x[2]=29;}for(int i=1;i<d.m;i++){day+=x[i];	}day+=d.d;System.out.println(day);return day;}public int DiffDays(test2 d){//计算两个日期之间的相距天数的成员方法 int s1=sum(this);int s2=sum(d);if(s1>s2){return s1-s2;}else{return s2-s1;}}public static void main(String args[]){ int a,b,c; test2 d1,d2; try{ d1=new test2(2020,02,03); d2=new test2(2025,03,02); System.out.println("相差的天数:"+d1.DiffDays(d2)); }catch(Exception e){ System.out.println("error"); } }