calendar type elements in a list

Question

I have to create a program which prints out a list of dates (year, month, days) until a users selected date (end_date which is later converted to end_cal).

For example, if today is 2017-09-30 Saturday and user inputs date 2017-10-30, program must print out these dates:

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

Problems:

1. Adding calendar type elements into a list
2. Printing the list.
3. Formatting dates during printing of addition to the list

When I try to print it, output is just a bunch of duplicates of same date.

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());

}

Input: 2018/01/01

Output (copied only one example, whole output is just several duplicates of this):

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]]

Answer 1

I'm not sure if this is the correct format for you (I will leave that as a task for you) but you could do something like this using LocalDate:

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);
    }
  }
}

Example Usage:

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

Answer 2

The first issue is with the way you print out the result:

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

If you want formatted dates, you will need to make use of a formatter.

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));
    }
}

A second issue is that you seem to reuse the same temp_cal object in your loop in getListOfDates. This results in your list containing multiple copies of the same Calendar object (which is modified multiple times). You will need to create a new instance for every iteration in your loop.

Answer 3

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);
    }
}

I think this is what you wanted, I didnt use a list but change it as you like.