列表中的日历类型元素

Posted 2023-02-25

【中文标题】列表中的日历类型元素

【英文标题】：calendar type elements in a list

【发布时间】：2018-03-12 02:47:28

【问题描述】：

我必须创建一个程序，它打印出日期列表（年、月、日），直到用户选择的日期（end_date 后来转换为end_cal）。

例如，如果今天是2017-09-30 Saturday，用户输入日期2017-10-30，程序必须打印出这些日期：

2017-09-30、2017-10-07、2017-10-14、2017-10-21、2017-10-28。

问题：

将日历类型元素添加到列表中 打印列表。 在打印添加到列表期间格式化日期

当我尝试打印它时，输出只是一堆相同日期的重复。

public class Weekdays 
    static Scanner input = new Scanner(System.in);
    static Calendar temp_cal = Calendar.getInstance(); //temporary calendar 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（仅复制一个示例，整个输出只是此示例的几个副本）：

java.util.GregorianCalendar[time=1515233525518,areFieldsSet=true,areAllFieldsSet=true,lenient=true,zone=sun.util.calendar.ZoneInfo[id="Europe/Helsinki",offset=7200000,dstSavings=3600000 ,useDaylight=true,transitions=118,lastRule=java.util.SimpleTimeZone[id=Europe/Helsinki,offset=7200000,dstSavings=3600000,useDaylight=true,startYear=0,startMode=2,startMonth=2,startDay=- 1,startDayOfWeek=1,startTime=3600000,startTimeMode=2,endMode=2,endMonth=9,endDay=-1,endDayOfWeek=1,endTime=3600000,endTimeMode=2]],firstDayOfWeek=2,minimalDaysInFirstWeek=4,ERA =1,YEAR=2018,MONTH=0,WEEK_OF_YEAR=1,WEEK_OF_MONTH=1,DAY_OF_MONTH=6,DAY_OF_YEAR=6,DAY_OF_WEEK=7,DAY_OF_WEEK_IN_MONTH=1,AM_PM=1,HOUR=0,HOUR_OF_DAY=12,MINUTE=12 ,SECOND=5,MILLISECOND=518,ZONE_OFFSET=7200000,DST_OFFSET=0]]

【问题讨论】：

我不能更强烈地建议您避免使用旧的 java.util.Calendar 类。您应该在 java.time 包中找到适合您用例的类。

Calendar 有方法before 和after 进行比较

java.time 包中的大多数（如果不是全部）类都实现了Comparable。

@JoeC 他们通常也有 isBefore 和 isAfter 方法（恕我直言，更具可读性）。

【参考方案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，而是根据你的喜好更改它。

【参考方案2】：

我不确定这是否适合您（我将把它作为一项任务留给您），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);
    
  

示例用法：

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

【参考方案3】：

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。这会导致您的列表包含同一日历对象的多个副本（多次修改）。您需要为循环中的每次迭代创建一个新实例。