/**
 * <p>年齡計算工具類</p>
 *
 * @author wangjs34383
 * @date 2020/12/23
 */

public class BirthdayUtil {

    public static int getAgeByBirth(Date birthDay) throws ParseException {
        int age = 0;
        Calendar cal = Calendar.getInstance();
        //出生日期晚於當前時間，無法計算
        if (cal.before(birthDay)) {
            throw new IllegalArgumentException(
                    "The birthDay is before Now.It's unbelievable!");
        }
        //當前年份
        int yearNow = cal.get(Calendar.YEAR);
        //當前月份
        int monthNow = cal.get(Calendar.MONTH);
        //當前日期
        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);
        //計算整歲數
        age = yearNow - yearBirth;
        if (monthNow <= monthBirth) {
            if (monthNow == monthBirth) {
                //當前日期在生日之前，年齡減一
                if (dayOfMonthNow < dayOfMonthBirth) {
                    age--;
                }
            } else {
                //當前月份在生日之前，年齡減一
                age--;
            }
        }
        return age;
    }
}