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造对象。birthday类中定义一个排序成员方法public boolean sort(Birthday birthnew),可以实现按年龄排序的操作。输入n(n<10)个人的生日信息，按照年龄大小顺序输出。用java写

以下是代码实现：

import java.time.LocalDate;
import java.time.Period;
import java.time.format.DateTimeFormatter;

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 birthdayStr) {
        DateTimeFormatter formatter = DateTimeFormatter.ofPattern("yyyy-MM-dd");
        LocalDate date = LocalDate.parse(birthdayStr, formatter);
        this.year = date.getYear();
        this.month = date.getMonthValue();
        this.day = date.getDayOfMonth();
    }

    public boolean sort(Birthday birthnew) {
        return this.compareTo(birthnew) < 0;
    }

    public int getAge() {
        LocalDate today = LocalDate.now();
        LocalDate birthday = LocalDate.of(year, month, day);
        return Period.between(birthday, today).getYears();
    }

    @Override
    public int compareTo(Birthday o) {
        int ageDiff = this.getAge() - o.getAge();
        if (ageDiff != 0) {
            return ageDiff;
        } else if (this.year != o.year) {
            return this.year - o.year;
        } else if (this.month != o.month) {
            return this.month - o.month;
        } else {
            return this.day - o.day;
        }
    }

    @Override
    public String toString() {
        return String.format("%04d-%02d-%02d", year, month, day);
    }
}

在主函数中，我们可以按照以下方式输入生日信息并排序输出：

import java.util.Arrays;
import java.util.Scanner;

public class Main {
    public static void main(String[] args) {
        Scanner input = new Scanner(System.in);
        System.out.print("请输入人数：");
        int n = input.nextInt();
        Birthday[] birthdays = new Birthday[n];
        for (int i = 0; i < n; i++) {
            System.out.printf("请输入第%d个人的生日（格式为yyyy-MM-dd）：", i + 1);
            String birthdayStr = input.next();
            birthdays[i] = new Birthday(birthdayStr);
        }
        Arrays.sort(birthdays);
        System.out.println("按年龄从小到大排序后的生日信息：");
        for (Birthday birthday : birthdays) {
            System.out.println(birthday);
        }
    }
}