Examples of 4 simple methods for calculating the number of days of date difference in java

public static void main(String[] args) {
		DateFormat dateFormat = new SimpleDateFormat("yyyy-MM-dd HH:mm:ss");
		 try {
		        Date startDate = ("2024-03-01 10:00:00");//Start time		        Date endDate = ("2024-03-02 14:00:00");//End time		        long msNum = ()-();//The number of milliseconds of the timestamp difference                long dayNum = msNum/(24*60*60*1000)//Divide by the milliseconds of a day to get the difference of days		        ("The difference of days is:"+ dayNum);
		 } catch (ParseException e) {
		        ();
		 }
}

public static void main(String[] args) {
		DateFormat dft = new SimpleDateFormat("yyyy-MM-dd");
	    try {
	        Date star = ("2020-02-03");//Start time	        Date endDay=("2025-03-02");//End time	        Date nextDay=star;
	        int i=0;
	        while((endDay)){// When tomorrow does not end time, it is to terminate the loop	        	Calendar cld = ();
	 	        (star);
	 	        (, 1);
	 	        star = ();
	 	        //Get the next day date string	 	        nextDay = star; 
	 	        i++;
	        }
	       ("The difference of days is:"+i);
	    } catch (ParseException e) {
	        ();
	    }
	}

public static void main(String[] args) {
		String star="2020-02-03";
		String end="2025-03-02";
		String[] star1=("-");
		String[] end1=("-");
		int days=0;
		if((star1[0])<(end1[0])){
			for(int i=(star1[0]);i<(end1[0]);i++){
				//Calculate whether it is Ruinian				if(i%4==0&&i%100!=0||i%400==0){
					days+=366;
				}else{
					days+=365;
				}
			}
		}
		//Get the date that has passed since the beginning of the year		int starday=days(star1[0],star1[1],star1[2]);
		//Get the date that ended that year has passed		int endday=days(end1[0],end1[1],end1[2]);
		//Subtract the date that has passed since the beginning of the year, plus the date that has passed when the end of the year.		days=days-starday+endday;
		("Date of difference:"+days);
	}
	public static int days(String year,String month,String day){
		int days=0;
		int nowyear=(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<(month);i++){
			if(flag){
				days+=monthday1[i];
			}else{
				days+=monthday[i];
			}
		}
		days+=(day);
		return days;
	}

int y;
	int m;
	int d;

	public test2(int y,int m,int d ){
		=y;
		=m;
		=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<;i++){
			if(i%4==0&& i%100!=0 || i%400==0){
				day+=366;
			}else{
				day+=365;
			}
		}
		if(%4==0&& %100!=0 || %400==0){
			x[2]=29;
		}
		for(int i=1;i<;i++){

			day+=x[i];	
		}
		day+=;
		(day);
		return day;

	}
	public int DiffDays(test2 d){//Member method for calculating the number of days apart between two dates		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); 
			("Date of difference:"+(d2)); 
		}catch(Exception e){ 
			("error"); 
		} 
	}

public int checkWeekendDay(int startDate, int endDate, int days){
        int weekEndCount = 0;
        if (days<1){
            if (startDate==6 || startDate==0){
                weekEndCount+=1;
            }
        } else {
            weekEndCount+=(days/7)*2;
            weekEndCount+=calculateWeekendDays(startDate,endDate);
        }

        return weekEndCount;
    }

public int calculateWeekendDays(int startDate, int endDate){
        int weekendCount=0;
        if (startDate==0&&endDate==6) {
            weekendCount += 2;
        }else if (startDate<endDate&&endDate==6){
            weekendCount+=1;
        }else if (startDate<endDate&&startDate==0){
            weekendCount+=1;
        }else if (startDate>endDate){
            weekendCount+=2;
        }
        if (startDate==endDate){
            if (startDate==6||endDate==0){
                weekendCount+=1;
            }
        }

        return weekendCount;
    }