Java Regular Expression match six digits

import java.util.regex.Pattern;

public class Main{
    public static void main(String[] argv) throws Exception{
        String str = "123";
        System.out.println(isValidCode(str));
        //from   www.j av  a 2  s .  c o  m
        str = "123123";
        System.out.println(isValidCode(str));
    }
    public static boolean isValidCode(String str) {
        if (str==null || str.length() == 0) {
            return false;
        }

        String regx = "^[0-9]{6}$";

        Pattern pattern = Pattern.compile(regx);
        return pattern.matcher(str).matches();
    }
    
}