Java剩余天数计算

Question

我已经实现了下面的代码来计算剩余的天数。我已经使用SimpleDateFormat将字符串转换为日期。如果输入10/02/1993（今天的日期）作为日期，则输出显示还剩0天。但如果我选择11/02/1993，它显示的输出与0天相同。但如果我改变月份，即1993年2月22日7月2日，它显示的是剩下160天，而不是原来的162天，这是原来的结果。我在这里做错了什么？非常感谢任何帮助。

private static void calculateNextBirthday() {
        Scanner in = new Scanner(System.in);
        System.out.println("Enter your birthday(dd/MM/yyyy)");
        user_input = in.nextLine();

        SimpleDateFormat formatter = new SimpleDateFormat("dd/MM/yyyy");

        Calendar user_selected_day = new GregorianCalendar();

        Calendar today = new GregorianCalendar();

        Date selected_date = null;
        try {
            selected_date = formatter.parse(user_input);
        } catch (ParseException e) {
            e.printStackTrace();
        }

        user_selected_day.setTime(selected_date);

        int user_selected_month = user_selected_day.get(Calendar.MONTH);
        int CMonth = today.get(Calendar.MONTH);

        int user_selected_date = user_selected_day.get(Calendar.DAY_OF_MONTH);
        int CDate = today.get(Calendar.DAY_OF_MONTH);

        user_selected_day.set(Calendar.YEAR, today.get(Calendar.YEAR));

        user_selected_day.set(Calendar.DAY_OF_WEEK,today.get(Calendar.DAY_OF_WEEK));

        if (user_selected_month < CMonth) {
            user_selected_day.set(Calendar.YEAR,today.get(Calendar.YEAR) + 1);
        }
        else if (user_selected_month == CMonth){
            if(user_selected_date < CDate){
                user_selected_day.set(Calendar.YEAR,today.get(Calendar.YEAR) + 1);  
            }
        }

        long millis = user_selected_day.getTimeInMillis() - today.getTimeInMillis();
        long days;
        days = (millis / (24 * 60 * 60 * 1000));

        System.out.println(String.valueOf(days) + " days left!!");
    }

更新：我已经更新了下面的代码，它工作良好。希望它对将来的人有所帮助。

`       SimpleDateFormat formatter = new SimpleDateFormat("dd/MM/yyyy");

        Calendar user_selected_day = new GregorianCalendar();

        Calendar today = new GregorianCalendar();

        Date selected_date = null;

        try {
            selected_date = formatter.parse(plainDate);
        } catch (ParseException e) {
            e.printStackTrace();
        }

        user_selected_day.setTime(selected_date);

        int user_selected_month = user_selected_day.get(Calendar.MONTH);
        int CMonth = today.get(Calendar.MONTH);

        int user_selected_date = user_selected_day.get(Calendar.DAY_OF_MONTH);
        int CDate = today.get(Calendar.DAY_OF_MONTH);

        user_selected_day.set(Calendar.YEAR, today.get(Calendar.YEAR));

        user_selected_day.set(Calendar.HOUR_OF_DAY,today.get(Calendar.HOUR_OF_DAY));
        user_selected_day.set(Calendar.MINUTE,today.get(Calendar.MINUTE));
        user_selected_day.set(Calendar.SECOND,today.get(Calendar.SECOND));
        user_selected_day.set(Calendar.MILLISECOND,today.get(Calendar.MILLISECOND));


        if (user_selected_month < CMonth) {
            user_selected_day.set(Calendar.YEAR,today.get(Calendar.YEAR) + 1);
        }
        else if (user_selected_month == CMonth){
            if(user_selected_date < CDate){
                user_selected_day.set(Calendar.YEAR,today.get(Calendar.YEAR) + 1);  
            }

        }

        long millis = user_selected_day.getTimeInMillis() - today.getTimeInMillis();
        long days;
        if(user_selected_day.getTime()==today.getTime()){
            days = 0;
        }
        else{
            days = (millis / (24 * 60 * 60 * 1000));
        }`

Answer 1

您还可以在Java 8中使用localdate类，随时添加/减去日期。

java.time提供了一个perio类来表示一段时间，例如天数或小时和分钟。localdate和friends提供plus()和minus()方法来添加或减去期间或其他与时间相关的对象。Period提供了工厂方法，如ofdays()。

阅读此示例以供参考。它计算从现在起700天后的日期：

/**
 * DateAdd -- compute the difference between two dates (e.g., today and 700 days
 * from now).
 */
public class Main {
    public static void main(String[] av) {
        /** Today's date */
        LocalDate now = LocalDate.now();
        Period p = Period.ofDays(700);
        LocalDate then = now.plus(p);
        System.out.printf("Seven hundred days from %s is %s%n", now, then);
    }
}

运行此程序将报告当前的日期和时间，以及从现在起七百天后的日期和时间。例如：

Seven hundred days from 2013-11-09 is 2015-10-10

Answer 2

问题出在线路上

user_selected_day.set(Calendar.YEAR, today.get(Calendar.YEAR));

这将把今天日期的年份设置为user_selectday，并且当month相等时，它将进入elseif内部并离开same而不做任何更改。

还要检查您提到的if else条件。