Algorithm to create X number of dates

Currently I have a list of Strings that represent a date in a yyyyMM format, something like this:

• 202008
• 202009
• 202010

I need to create x number of entries in this list with each entry increasing the month by one, so if I were to create 3 new entries they would look like this:

• 202011
• 202012
• 202101

Currently my idea is to create a method to pick the latest date, parse the String to separate month and year, increase the month value by 1 if it is < 12 otherwise set it to 1 and increase the year instead. Then I would add that value to a list and set it as the most recent, repeating x number of times.

What I want to know is if there is a more elegant solution that I could use, maybe using an existing date library (I’m using Java).

Answer

YearMonth And DateTimeFormatter

I recommend you do it using these modern date-time classes as shown below:

import java.time.YearMonth;
import java.time.format.DateTimeFormatter;
import java.util.ArrayList;
import java.util.List;

public class Main {
    public static void main(String[] args) {
        // Test
        List<String> list = getYearMonths("202011", 3);
        System.out.println(list);

        // Bonus: Print each entry of the obtained list, in a new line
        list.forEach(System.out::println);
    }

    public static List<String> getYearMonths(String startWith, int n) {
        List<String> list = new ArrayList<>();

        // Define Formatter
        DateTimeFormatter formatter = DateTimeFormatter.ofPattern("uuuuMM");

        // Parse the year-month string using the defined formatter
        YearMonth ym = YearMonth.parse(startWith, formatter);

        for (int i = 1; i <= n; i++) {
            list.add(ym.format(formatter));
            ym = ym.plusMonths(1);// Increase YearMonth by one month
        }
        return list;
    }
}

Output:

[202011, 202012, 202101]
202011
202012
202101

Learn more about the modern date-time API at Trail: Date Time.