Validate ID Number

Here is a code that check whether the south African Id is valid or not.

import java.util.*;
import java.util.regex.*;

class  ValidateSouthAfricanID
{
public static boolean isValidIdNumber(String idNumber) {
        String regExpression = "([0-9][0-9])((?:[0][1-9])|(?:[1][0-2]))((?:[0-2][0-9])|(?:[3][0-1]))([0-9])([0-9]{3})([0-9])([0-9])([0-9])"; 
        Pattern pattern = Pattern.compile(regExpression);

        Matcher matcher = pattern.matcher(idNumber);

        if (matcher.matches()) {

            int tot1 = 0;
            for (int i = 0; i < idNumber.length() - 1; i += 2) {
                tot1 = tot1 + Integer.parseInt(idNumber.substring(i, i + 1));
            }

            StringBuffer field1 = new StringBuffer("");
            for (int i = 1; i < idNumber.length(); i += 2) {
                field1.append(idNumber.substring(i, i + 1));
            }

            String evenTotStr = (Long.parseLong(field1.toString()) * 2) + "";
            int tot2 = 0;
            for (int i = 0; i < evenTotStr.length(); i++) {
                tot2 = tot2 + Integer.parseInt(evenTotStr.substring(i, i + 1));
            }

            int lastD = (10 - ((tot1 + tot2) % 10)) % 10;
            int checkD = Integer.parseInt(idNumber.substring(12, 13));

            if (checkD == lastD) {
                return true;
            } else {
                return false;
            }
        } else {
            return false;
        }
    }

    public static void main(String[] args) 
    {
        Scanner input=new Scanner(System.in);
        System.out.println("Enter South African ID: ");
        String id=input.nextLine();
        if(isValidIdNumber(id)){
            System.out.println("Valid");
        }
        else{
            System.out.println("Not Valid");
        }

    }
}