年龄Age的计算（可以精确到1岁3个月10天）

import java.text.SimpleDateFormat

/**
 * 年龄对象（3岁、3个月、30天）
 */
class Age {
    Integer age
    AgeUnit unit

    Integer year
    Integer month
    Integer day

    Age() {

    }

    Age(int age) {
        this.age = age
        unit = AgeUnit.YearOfAge
    }

    Age(String str) {
        def regular = /^(\d+)(\S+)?/
        if (!(str ==~ regular)) {
            throw new IllegalArgumentException("不是年龄格式")
        }
        def result = (str =~ regular)           //拆分
        age = Integer.parseInt(result[0][1])
        unit = result[0][2] ? AgeUnit.getUnitBySymbol(result[0][2]) : AgeUnit.YearOfAge
    }

    Age(int age, AgeUnit unit) {
        this.age = age
        this.unit = unit
    }

    Age(Date birthday) {
        this(birthday, new Date())
    }

    Age(Date birthday, Date today) {
        Calendar birthdayCalender = Calendar.getInstance()
        birthdayCalender.setTime(birthday)
        Calendar todayCalender = Calendar.getInstance()
        todayCalender.setTime(today)
        day = todayCalender.get(Calendar.DAY_OF_MONTH) - birthdayCalender.get(Calendar.DAY_OF_MONTH);
        month = todayCalender.get(Calendar.MONTH) - birthdayCalender.get(Calendar.MONTH);
        year = todayCalender.get(Calendar.YEAR) - birthdayCalender.get(Calendar.YEAR);
        //按照减法原理，先day相减，不够向month借；然后month相减，不够向year借；最后year相减。
        if (day < 0) {
            month -= 1;
            todayCalender.add(Calendar.MONTH, -1);//得到上一个月，用来得到上个月的天数。
            day = day + todayCalender.getActualMaximum(Calendar.DAY_OF_MONTH);
        }
        if (month < 0) {
            month = (month + 12) % 12;
            year--;
        }
        if (year > 0) {
            age = year
            unit = AgeUnit.YearOfAge
        } else if (month > 0) {
            age = month
            unit = AgeUnit.MonthOfAge
        } else {
            age = day
            unit = AgeUnit.DayOfAge
        }
    }

    public String display() {
        return age + unit
    }

    public String toString() {
        return "Age{" +
                "age=" + age +
                ", unit=" + unit +
                ", year=" + year +
                ", month=" + month +
                ", day=" + day +
                '}';
    }
}

enum AgeUnit {
    YearOfAge("岁"),
    MonthOfAge("个月"),
    DayOfAge("天");

    private String symbol;

    AgeUnit(String symbol) {
        this.symbol = symbol;
    }

    public String getSymbol() {
        return symbol;
    }

    @Override
    public String toString() {
        return symbol;
    }

    public static AgeUnit getUnitBySymbol(String val) {
        val = val.trim().toLowerCase();
        if ("岁".equals(val)) return YearOfAge;
        else if ("个月".equals(val)) return MonthOfAge;
        else if ("月".equals(val)) return MonthOfAge;
        else if ("天".equals(val)) return DayOfAge;
        throw new IllegalArgumentException(val + "不是合法的年龄单位");
    }
}

class AgeTest extends GroovyTestCase {
    def testAge() {
        Date date = new SimpleDateFormat("yyyy-MM-dd").parse("2008-07-01")
        Date today = new SimpleDateFormat("yyyy-MM-dd").parse("2011-07-01")
        def age = new Age(date, today)
        println age
        // Age{age=3, unit=岁, year=3, month=0, day=0}
    }
}