有JAVA怎么根据年龄求出出身年月

public static int getAge(Date birthDay) throws Exception {        Calendar cal = Calendar.getInstance();        if (cal.before(birthDay)) {            throw new IllegalArgumentException(                "The birthDay is before Now.It's unbelievable!");        }        int yearNow = cal.get(Calendar.YEAR);        int monthNow = cal.get(Calendar.MONTH);        int dayOfMonthNow = cal.get(Calendar.DAY_OF_MONTH);        cal.setTime(birthDay);        int yearBirth = cal.get(Calendar.YEAR);        int monthBirth = cal.get(Calendar.MONTH);        int dayOfMonthBirth = cal.get(Calendar.DAY_OF_MONTH);        int age = yearNow - yearBirth;        if (monthNow <= monthBirth) {            if (monthNow == monthBirth) {                if (dayOfMonthNow < dayOfMonthBirth) age--;            }else{                age--;            }        }        System.out.println("age:"+age);        return age;    }
------解决方案--------------------------------------------------------
那就要年龄具体到月才行，比如满20周岁多3个月5天 输入 20，3，5 作为参数，这样可以推算，否则只知道周岁，只能推算出生年

for example
Java code
public static String getBirthday(int ageYear, int ageMonth, int ageDay) {    Calendar c = Calendar.getInstance();    c.add(Calendar.YEAR, -ageYear);    c.add(Calendar.MONTH, -ageMonth);    c.add(Calendar.DAY_OF_MONTH, -ageDay);    return String.format("%tF", c.getTime());}//调用String birthday = getBirthday(20, 3, 5);System.out.println(birthday);