列表中的日历类型元素

Question

我必须创建一个程序，打印出日期列表（年、月、日），直到用户选择日期（end_date，稍后转换为end_cal）。

例如，如果今天是2017-09-30星期六，并且用户输入日期是2017-10-30，程序必须打印这些日期：

2017-09-30, 2017-10-07, 2017-10-14, 2017-10-21, 2017-10-28.

问题：

1. 将日历类型元素添加到列表中

当我试图打印它时，输出只是一堆相同日期的副本。

public class Weekdays {
    static Scanner input = new Scanner(System.in);
    static Calendar temp_cal = Calendar.getInstance(); //temporary calendar html" target="_blank">object. it's value is being chaged in the process
    static Calendar start_cal = Calendar.getInstance(); // current day when the program is executed
    static Calendar end_cal = Calendar.getInstance(); //end date that the user inputs


static SimpleDateFormat format = new SimpleDateFormat("yyyy/MM/dd");

public static boolean date_validation(String date){  //partial validation: whether the input date is in a correct format
    Date test_date;
    try {
        test_date = format.parse(date);

    }catch (ParseException e){
        return false;
        }
    return true;
}   
//created list of dates that are of the same day of the week (for example all Sundays)
static private List<Calendar> getListOfDates(){
    List<Calendar> dates = new ArrayList<>();
    while (!((temp_cal.get(Calendar.YEAR)>= end_cal.get(Calendar.YEAR))&&(temp_cal.get(Calendar.MONTH) >= end_cal.get(Calendar.MONTH))&&(temp_cal.get(Calendar.DAY_OF_YEAR) >= end_cal.get(Calendar.DAY_OF_YEAR))))
    {   
            temp_cal.add(Calendar.DATE, 7); 
            dates.add(temp_cal);        }
    return dates;
}

static private void printListOfDates(List<Calendar> dates){

            System.out.println(Arrays.toString(dates.toArray()));
}

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

    String end_date = input.next();

    while(!(date_validation(end_date))){
        end_date = input.next();
    }

    end_cal.setTime(format.parse(end_date));    

    printListOfDates(getListOfDates());

}

输入：2018/01/01

输出（仅复制了一个示例，整个输出只是此示例的几个副本）：

JAVAutil。GregorianCalendar[time=1515233525518，areFieldsSet=true，ArealFieldsSet=true，lenient=true，zone=sun.util.calendar.ZoneInfo[id=“Europe/Helsinki”，offset=7200000，DSTSAVAINGS=3600000，useDaylight=true，transitions=118，lastRule=java.util.SimpleTimeZone[id=欧洲/赫尔辛基（id=欧洲/赫尔辛基，偏移量=7200000，DST=7200000，DST=0，startMode=2，startMode=2，startDay=2，startDay=1，StartDayOWeek=1，startDay=1，startDay=2，startDay=1，startDay=1，StartDayOOOwWeek=1，StartDayOwWeek=1，StartDayWeek=1，StartDayOwwwEEEEEk=1，StartWayWeek=1，StartDayEEk=1，StartDayOwwwwEEEEEEEk=1，StartWek=1，StartDayEEE8=1，Start=1，Start=1，Start=1，Start=1，StartDayOwwwwwEEEE，周中的天，月中的上午下午1点，小时0点，日中的小时12点，分钟12点，秒5点，毫秒518点，区域偏移量7200000点，DST偏移量0点]]

Answer 1

import java.util.Date;
import java.time.*;
import java.text.SimpleDateFormat;
import java.util.*;
public class days
{
public static void main (String args[]){
    Scanner input = new Scanner(System.in);
    System.out.println("Enter Dates (Start(yyyy/mm/dd)-End)");
    //example 2017 1 5 -> 5 jan 2017
    getDates(Integer.parseInt(input.next()),Integer.parseInt(input.next()),
                 Integer.parseInt(input.next()),Integer.parseInt(input.next()),
                    Integer.parseInt(input.next()),Integer.parseInt(input.next()));
    /*the input needed example
     * 2017
     * 1
     * 1      -Start date
     * 2017
     * 2
     * 10     -End date
     */

}

public static void getDates(int pYearStart, int pMonthStart, int pDayStart,
                                    int pYearEnd, int pMonthEnd, int pDayEnd){
    SimpleDateFormat sdf = new SimpleDateFormat("yyyy MMM dd");
    int year = pYearStart;
    int month = pMonthStart-1;
    int day = pDayStart;
    Calendar start = new GregorianCalendar(year,month,day);
    int yearEnd = pYearEnd;
    int monthEnd = pMonthEnd-1;
    int dayEnd = pDayEnd;
    Calendar end = new GregorianCalendar(yearEnd,monthEnd,dayEnd);
    System.out.print("Start Date:   ");
    System.out.println(sdf.format(start.getTime()));

    System.out.print("End Date:   ");
    System.out.println(sdf.format(end.getTime()));

    System.out.println("");
    System.out.println("All Dates:");

    boolean sameDate = false;
    int amount = 0;
    do{

        System.out.println(sdf.format(start.getTime()));
        start.add(Calendar.DAY_OF_MONTH, 7);
        amount++;
        if(start.get(Calendar.DAY_OF_MONTH) >= end.get(Calendar.DAY_OF_MONTH) && 
        start.get(Calendar.MONTH) == end.get(Calendar.MONTH)) {
            sameDate = true;}
    }while(sameDate != true);
    System.out.println("No of dates: "+amount);
    }
}

我想这就是你想要的，我没有使用列表，而是根据你的喜好进行更改。

Answer 2

第一个问题是打印结果的方式：

System.out.println(Arrays.toString(dates.toArray()));

如果您想要格式化日期，则需要使用格式化程序。

private static SimpleDateFormat outputFormat = new SimpleDateFormat("yyyy-MM-dd");

static private void printListOfDates(List<Calendar> dates){
    for (Calendar date : dates) {
        System.out.println(outputFormat.format(date));
    }
}

第二个问题是，您似乎在getListOfDates的循环中重用了相同的temp_cal对象。这将导致列表中包含同一日历对象的多个副本（该日历对象已被修改多次）。您需要为循环中的每个迭代创建一个新实例。

Answer 3

我不确定这是否适合您（我会将其作为您的任务），但您可以使用LocalDate执行类似的操作：

import java.util.Scanner;
import java.time.LocalDate;
import java.time.format.DateTimeFormatter;

class Main {
  public static void main(String[] args) {
    Scanner scanner = new Scanner(System.in);

    DateTimeFormatter formatter = DateTimeFormatter.ofPattern("yyyy/MM/dd");
    LocalDate endDate;

    while(true){
      System.out.print("Enter the endDate in the format of yyyy/MM/dd:");
      String date = scanner.next();
      try {
        endDate = LocalDate.parse(date, formatter);
        break;
      } catch (Exception e) {
        System.err.println("ERROR: Please input the date in the correct format");
      }
    }

    System.out.println("Below are the days between the current day and " + endDate);
    printDaysBetween(endDate);
  }

  public static void printDaysBetween(LocalDate end){
    LocalDate start = LocalDate.now();
    while (!start.isAfter(end)) {
      System.out.println(start);
      start = start.plusDays(7);
    }
  }
}

用法示例：

Enter the endDate in the format of yyyy/MM/dd: 2017-10-30
ERROR: Please input the date in the correct format
Enter the endDate in the format of yyyy/MM/dd: 2017/10/30
Below are the days between the current day and 2017-10-30
2017-09-30
2017-10-07
2017-10-14
2017-10-21
2017-10-28