public class PassportFields
{
    private PassportFields ()
    {
    }
}
public class PassportFields
{
    public static final String BIRTH_YEAR = "byr";
    public static final String ISSUE_YEAR = "iyr";
    public static final String EXPORATION_YEAR = "eyr";
    public static final String HEIGHT = "hgt";
    public static final String HAIR_COLOUR = "hcl";
    public static final String EYE_COLOUR = "ecl";
    public static final String PASSPORT_ID = "pid";
    public static final String COUNTRY_ID = "cid";

    private PassportFields ()
    {
    }
}
Update PassportFields.java