使用Java定义一个birthday类,包括年、月、日三个成员变量。默认创建一个“2000-01-01”的对象,否则按照提供的日期字符串创建对象。birthday类中定义一个排序成员方法,可以实现按年龄排序的操作。输入n个人的生日信息,按照年龄大小顺序输出

以下是Java定义的Birthday类实现：

import java.time.LocalDate;
import java.time.Period;
import java.util.ArrayList;
import java.util.Collections;
import java.util.List;

public class Birthday implements Comparable<Birthday> {
    private int year;
    private int month;
    private int day;

    public Birthday() {
        this.year = 2000;
        this.month = 1;
        this.day = 1;
    }

    public Birthday(String dateStr) {
        LocalDate date = LocalDate.parse(dateStr);
        this.year = date.getYear();
        this.month = date.getMonthValue();
        this.day = date.getDayOfMonth();
    }

    public void setYear(int year) {
        this.year = year;
    }

    public void setMonth(int month) {
        this.month = month;
    }

    public void setDay(int day) {
        this.day = day;
    }

    public int getYear() {
        return year;
    }

    public int getMonth() {
        return month;
    }

    public int getDay() {
        return day;
    }

    public int compareTo(Birthday o) {
        LocalDate date1 = LocalDate.of(year, month, day);
        LocalDate date2 = LocalDate.of(o.getYear(), o.getMonth(), o.getDay());
        Period period1 = Period.between(date1, LocalDate.now());
        Period period2 = Period.between(date2, LocalDate.now());
        return period1.getYears() - period2.getYears();
    }

    public static void main(String[] args) {
        List<Birthday> birthdays = new ArrayList<>();
        birthdays.add(new Birthday("1995-05-13"));
        birthdays.add(new Birthday("1990-08-20"));
        birthdays.add(new Birthday("1988-12-01"));
        birthdays.add(new Birthday("1998-02-28"));
        birthdays.add(new Birthday());

        Collections.sort(birthdays);

        for (Birthday birthday : birthdays) {
            System.out.println(birthday.getYear() + "-" + birthday.getMonth() + "-" + birthday.getDay());
        }
    }
}

在这个实现中，我们使用了Java 8中的LocalDate类来处理日期，并使用Period类计算年龄。compareTo方法通过比较两个生日日期的年龄大小来实现排序。在main方法中，我们创建了一个包含多个生日对象的List，然后使用Collections.sort方法按照年龄从小到大排序，并输出结果。