日历减去日期问题

Question

我有一个几乎完成的脚本，但有一个小问题我似乎无法修复。

首先让我快速解释一下脚本。它使用Calendar 获取当前日期。然后它在当前日期上添加 2 天，然后创建格式，以更改新日期的格式。然后它将新日期打印到 .txt 文件中，然后使用 Scanner 从 .txt 文件中获取该日期。然后在这里，我遇到了一些小麻烦。我从 .txt 文件中获得的新日期，我想从实际的当前日期中减去。因此，我可以从当前系统日期开始倒计时，直到 2 天。目前，代码正在减法/倒计时函数中使用日期变量 todAdd 进行减法，这是代码的最后 6 行。但我希望它不是那个日期变量，而是dateFroText 变量，但我无法将它解析为最后一个减法代码，因为它似乎没有很好地处理变量的解析。

所以基本上举个例子，我希望整个倒计时部分将todAdd 更改为dateFroText。因此，而不是您在下面的完整代码中看到的行，它将像这样 int yearDiff = dateFroText.get(Calendar.YEAR) - startDat.get(Calendar.YEAR);

目前我已尝试将其更改为integer、string 和date，但它们都会产生一个错误，导致无法运行代码。

如有必要，我已经复制了整个代码，因此您可以实际测试它。

public class CdowTDate
{

    static File dFileD = new File("date.txt");
    static String date = "";

  public static void main(String[] args) throws ParseException {

      //Get current date and time
      Calendar startDat = Calendar.getInstance();
      System.out.println("Current date: " + startDat.getTime());

      //Get that current date and time and then add 2 days
      Calendar todAdd = Calendar.getInstance();
      todAdd.add(Calendar.DATE, 2);
      System.out.println("Date in 2 days: " + todAdd.getTime());

      //Create a format for sending date to text file
      SimpleDateFormat formDat = new SimpleDateFormat("EEE, d MMM yyyy HH:mm:ss Z");
      String formatted = formDat.format(todAdd.getTime());
      System.out.println("Formatted: " + formatted);

      try{
          PrintWriter dW = new PrintWriter("date.txt");
          dW.println(formatted);
          dW.close();
      } catch (IOException e) {
      }

      System.out.println(formDat.parse(formatted));

      try {
          Scanner dateRead = new Scanner(dFileD);
          while (dateRead.hasNextLine()) {
              date = dateRead.nextLine();
              Date dateFroText = formDat.parse(date);
              System.out.println("Date from text new format: " + dateFroText);
          }
          dateRead.close();
        } catch (Exception e) {
            System.out.println("Error!");
        }

      int yearDiff = todAdd.get(Calendar.YEAR) - startDat.get(Calendar.YEAR);
      int dayDiff = ((yearDiff*365) + todAdd.get(Calendar.DAY_OF_YEAR)) - startDat.get(Calendar.DAY_OF_YEAR);
      dayDiff--;
      int hourDiffer = todAdd.get(Calendar.HOUR_OF_DAY)+23 - startDat.get(Calendar.HOUR_OF_DAY);
      int minuDiff = todAdd.get(Calendar.MINUTE)+60 - startDat.get(Calendar.MINUTE);
      System.out.println(dayDiff + " days " + hourDiffer + " hours " + minuDiff +" minutes remaining");


  }

}

Answer 1

您需要将日期对象 dateFroTxt 转换为 Calendar 对象来进行计算。

public static void main(String[] args) throws ParseException {

        //Get current date and time
        Calendar startDat = Calendar.getInstance();
        System.out.println("Current date: " + startDat.getTime());

        //Get that current date and time and then add 2 days
        Calendar todAdd = Calendar.getInstance();
        todAdd.add(Calendar.DATE, 2);
        System.out.println("Date in 2 days: " + todAdd.getTime());

        //Create a format for sending date to text file
        SimpleDateFormat formDat = new SimpleDateFormat("EEE, d MMM yyyy HH:mm:ss Z");
        String formatted = formDat.format(todAdd.getTime());
        System.out.println("Formatted: " + formatted);

        try {
            PrintWriter dW = new PrintWriter("date.txt");
            dW.println(formatted);
            dW.close();
        } catch (IOException e) {
        }

        System.out.println(formDat.parse(formatted));

        Date dateFroText = null;
        try {
            Scanner dateRead = new Scanner(dFileD);
            while (dateRead.hasNextLine()) {
                date = dateRead.nextLine();
                dateFroText = formDat.parse(date);
                System.out.println("Date from text new format: " + dateFroText);
            }
            dateRead.close();
        } catch (Exception e) {
            System.out.println("Error!");
        }

        if (dateFroText != null) {
            Calendar dateFromTxtCal = Calendar.getInstance();
            dateFromTxtCal.setTime(dateFroText);
            int yearDiff = dateFromTxtCal.get(Calendar.YEAR) - startDat.get(Calendar.YEAR);
            int dayDiff = ((yearDiff * 365) + dateFromTxtCal.get(Calendar.DAY_OF_YEAR)) - startDat.get(Calendar.DAY_OF_YEAR);
            dayDiff--;
            int hourDiffer = dateFromTxtCal.get(Calendar.HOUR_OF_DAY) + 23 - startDat.get(Calendar.HOUR_OF_DAY);
            int minuDiff = dateFromTxtCal.get(Calendar.MINUTE) + 60 - startDat.get(Calendar.MINUTE);
            System.out.println(dayDiff + " days " + hourDiffer + " hours " + minuDiff + " minutes remaining");
        }
    }