java根据出生日期获得年龄

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;

    }