剩余天数计算 java

Question

我已经实现了以下代码来计算剩余天数。我使用 SimpleDateFormat 将字符串转换为日期。如果我输入 10/02/1993（今天的日期）作为日期，输出显示还剩 0 天。但是如果我选择 11/02/1993，它会显示与剩余 0 天相同的输出。但是，如果我更改月份，即 22/07/1993，它会显示剩余 160 天，而不是原始结果的 162 天。我在这里做错了什么？任何帮助是极大的赞赏。

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!!");
    }

UPDATE : I have updated the Code below and it works fine. Hope it helps someone in the future.

`       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

不要自己计算。拥有 Calendar 对象后，使用 "add" 方法增加所需的值。

Answer 2

问题出在行

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

这会将今天日期的年份设置为 user_selected 日，并且由于月份相等，它将进入 elseif 并在不进行任何更改的情况下退出.

还要检查您提到的 if else 条件。

Answer 3

您还可以在 Java 8 中使用 LocalDate class，add/subtract 约会。

java.time offers a Period class to represent a length of time, such as a number of days, or hours and minutes. LocalDate and friends offer plus() and minus() methods to add or subtract a Period or other time-related object. Period offers factory methods such as 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);
    }
}

运行该程序报告当前日期和时间，以及七百天后的日期和时间。例如：

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

剩余天数计算 java

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