Validates a Swedish personal identity number.

validatePersonnummer.java

package com.example;

import java.text.DateFormat;
import java.text.ParseException;
import java.text.SimpleDateFormat;
import java.util.regex.*;

public class Main {

    final static String DATE_FORMAT = "yyMMdd";

    public static void main(String[] args) {
        if (args.length != 1) {
            System.err.println("Enter one argument as a personnummer.");
            System.exit(1);
        }

        String personnummer = args[0];

        if (!checkFormat(personnummer)) {
            System.err.println("Incorrect format.");
            System.exit(2);
        }

        personnummer = transformTo10Digits(personnummer);

        Boolean validDate = validateDate(personnummer.substring(0,6));

        Boolean samordningsnummer = isSamordningsnummer(personnummer);

        if (!validDate && !samordningsnummer){
            System.out.println(personnummer + " has an invalid date.");
            System.exit(3);
        }

        Boolean valid = validateLuhnChecksum(personnummer);

        System.out.println(personnummer + " is " + (valid ? "valid" : "invalid") + (samordningsnummer ? " and is a samordningsnummer" : "") + ".");
        System.exit(valid ? 0 : 3);
    }

    private static Boolean isSamordningsnummer(String personnummer) {
        System.out.println("samord" + personnummer.substring(4,6));
        Boolean isSamordningsnummer = false;
        int day = Integer.parseInt(personnummer.substring(4,6));
        if (day > 60 && day < 92) {
            isSamordningsnummer = true;
        }
        return isSamordningsnummer;
    }

    private static Boolean validateLuhnChecksum(String personnummer) {
        int checksum = 0;
        String[] pnarr = personnummer.split("");
        for (int i = 0; i < personnummer.length(); i++) {
            int n = Integer.parseInt(pnarr[i]);
            if (i % 2 == 0) {
                n *= 2;
                if (n > 9) {
                    n = (n % 10) + 1;
                }
            }
            checksum += n;
        }
        return checksum % 10 == 0;
    }

    private static String transformTo10Digits(String personnummer) {
        // Remove - or +.
        personnummer = personnummer.replaceAll("[-\\+]", "");

        // Strip century if included.
        if (personnummer.length() == 12) {
            personnummer = personnummer.substring(2);
        }
        return personnummer;
    }

    private static boolean checkFormat(String personnummer) {
        // Checks that the personnummer is 10 or 12 digits
        // with optional - or + before the last 4.
        Pattern p = Pattern.compile("^\\d{6}(?:\\d{2})?[-\\s\\+]?\\d{4}$");
        Matcher m = p.matcher(personnummer);
        return m.matches();
    }

    public static boolean validateDate(String date)
    {
        try {
            DateFormat df = new SimpleDateFormat(DATE_FORMAT);
            df.setLenient(false);
            df.parse(date);
            return true;
        } catch (ParseException e) {
            return false;
        }
    }
}

Run as
java personnummer com.example.Main 190910799824