BookMgr第一部分
public class BookMgr {
    public String name; //图书名称
    public String state; //图书状态
    public Date date;   //借出时间
    public void setBookMgr(String mingzi, String zhuangtai, Date jiechuriqi){
        name = mingzi;
        state=zhuangtai ;
        date = jiechuriqi;
    }

    public void setBookMgr(int index) {
        System.out.println(index+ "\t" + state+ "\t" +name  + "\t" + date );
    }


}

BookMgr第二部分
public class BookSet {

    BookMgr []stockroom= new BookMgr[100];
}

BookManage第三部分
package Demo03;

import java.text.DateFormat;
import java.text.ParseException;
import java.text.SimpleDateFormat;
import java.util.Date;
import java.util.Scanner;

/**
 * @author huxiaomei
 * @date 2021/4/9 8:05
 */
public class BookManage {
    BookSet bookSet = new BookSet();

    //存储商品
    public void initial() {
        BookMgr java = new BookMgr();
        java.setBookMgr("《java基础教程》", "已借出", new Date());

        BookMgr shujuku = new BookMgr();
        shujuku.setBookMgr("《数据库技术》", "可借", null);

        BookMgr renyueshenhua = new BookMgr();
        renyueshenhua.setBookMgr("《人月神话》", "可借", null);
        bookSet.stockroom[0] = java;
        bookSet.stockroom[1] = shujuku;
        bookSet.stockroom[2] = renyueshenhua;
    }

    //启动菜单
    public void startMenu() throws ParseException {
        boolean flag = true;
        do {
            System.out.println("欢迎使用图书管理系统");
            System.out.println("******************************");
            System.out.println("1.新增图书");
            System.out.println("2.查看图书");
            System.out.println("3.删除图书");
            System.out.println("4.借出图书");
            System.out.println("5.归还图书");
            System.out.println("6.退  出");
            System.out.println("请选择：");
            Scanner scanner = new Scanner(System.in);

            int num = scanner.nextInt();
            switch (num) {
                case 1:
                    System.out.println("---> 新增图书");
                    xinzeng();
                    break;
                case 2:
                    System.out.println("---> 查看图书");
                    chakan();
                    break;
                case 3:
                    System.out.println("---> 删除图书");
                    shanchu();
                    break;
                case 4:
                    System.out.println("---> 借出图书");
                    jiechu();
                    break;
                case 5:
                    System.out.println("---> 归还图书");
                    guihuan();
                    break;
                case 6:
                    System.out.println("谢谢使用！");
                    flag = false;
                    break;
                default:
                    System.out.println("你输入错误，请再次输入");

            }

        } while (flag);

    }
    private void xinzeng() {
        System.out.println("请输入图书名称：");
        Scanner scanner = new Scanner(System.in);
        String mingzi = scanner.next();
        System.out.println("新增" + mingzi + "成功");
        BookMgr tushu4 = new BookMgr();
        bookSet.stockroom[3] = tushu4;
        tushu4.setBookMgr(tushu4.name, tushu4.state, tushu4.date);

        for (int i = 0; i < bookSet.stockroom.length; i++) {


            if (bookSet.stockroom[i] == null) {
                bookSet.stockroom[i] = new BookMgr(); // 把新建的对象放在数组中的第一个空位置
                break; // 后续的空位置直接跳过
            }
        }
    }

    private void chakan() {
        System.out.println("编号 \t 状态 \t 名称 \t 借出日期");
        for (int i = 0; i < bookSet.stockroom.length; i++) {
            if (bookSet.stockroom[i] != null) {
                bookSet.stockroom[i].setBookMgr(i + 1);
            }
        }
    }

    private void shanchu() {
        System.out.println("请输入图书名称");
        Scanner scanner = new Scanner(System.in);
        String bianhao = scanner.next();
        boolean flag = true;
        for (int i = 0; i < bookSet.stockroom.length; i++) {
            if (bookSet.stockroom[i] != null && bookSet.stockroom[i].name==bianhao && bookSet.stockroom[i].state=="可借") {
                int j = i;
                while (bookSet.stockroom[j + 1] != null) {
                    //后面的元素向前移动
                    bookSet.stockroom[j] = bookSet.stockroom[j + 1];
                    j++;
                }
                bookSet.stockroom[j] = null;
                System.out.println("删除"+bianhao+"成功");
                break;   //后面的空数组元素没有必要执行
            }else {
                System.out.println(bianhao + "为借出状态，不能删除");
            }

        }
    }
    private void jiechu() throws ParseException {
        System.out.println("请输入图书名称：");
        Scanner scanner = new Scanner(System.in);
        String tushuming = scanner.next();
        System.out.println("请输入借出日期（年-月-日）：");
        String riqi = scanner.next();
        DateFormat format = new SimpleDateFormat("yyyy年MM月dd日");
        Date date1 = format.parse(riqi);

            for(int i = 0;i <bookSet.stockroom.length-1;i++){
                if(bookSet.stockroom[i] != null && bookSet.stockroom[i].name == tushuming && bookSet.stockroom[i].state =="可借"){
                    bookSet.stockroom[i].state = "已借出";
                    bookSet.stockroom[i].date = date1;
                    System.out.println("借出"+tushuming +"成功");
                }
            }

    }
    private void guihuan() throws ParseException {
        int num = 0;
        Scanner scanner = new Scanner(System.in);
        System.out.println("请输入图书名称：");
        String guihuantushu = scanner.next();
        System.out.println("请输入归还日期（年-月-日）：");
        String riqi2 = scanner.next();
        DateFormat format = new SimpleDateFormat("yyyy年MM月dd日");
        Date date2 = format.parse(riqi2);
        for (int i = 0;i<bookSet.stockroom.length;i++){
            if (bookSet.stockroom[i].name == guihuantushu && bookSet.stockroom[i] != null && bookSet.stockroom[i].state == "已借出"){
                System.out.println("借出时间"+bookSet.stockroom[i].state);
                System.out.println("归还时间"+ date2);
                long alnteger=((bookSet.stockroom[i].date.getTime()-date2.getTime())/(24*60*60*1000));
                num=(int)alnteger;
                System.out.println("需要支付"+num+"元");
                System.out.println("归还"+guihuantushu+"成功");
                bookSet.stockroom[i].state="可借";
                bookSet.stockroom[i].date=null;
            }
        }
    }
}

 Booktest第四部分
public class Booktest {
    public static void main(String[] args) throws ParseException {
        BookManage bookManage = new BookManage();
        bookManage.initial();
        bookManage.startMenu();
    }
}