package imooc_homework;

import java.util.InputMismatchException;
import java.util.Scanner;

public class Library_demo1 {
    public static void main (String[] main){
        Book[] books = {
            new Book("论语",1),
            new Book("高数",2),
            new Book("电路",3),
            new Book("大英",4)
        };  

        System.out.println("--------图书系统--------");
        System.out.println("输入命令：1-按名称查书；2-按序号查书");

        // 驗證命令是否錯誤
        int checkStatus = 0;
        while (true) {
            checkStatus = systemCheckCallack();
            if( checkStatus != 1 && checkStatus != 2 )
                System.out.println("命令错误，请重新输入！");
            else break;
        }

        while(true) {
             boolean exit = false;

            // 找name
            if(checkStatus == 1) {
                System.out.print("请输入图书名称(name)：");
                Scanner scan = new Scanner(System.in); // 使用者輸入 "大英"
                String bookName = scan.next(); // 使用者輸入字串(不包含空格和tag)

                for (Book bookData : books) {
                    if(bookName.equals(bookData.name)) {
                        System.out.println( "找到图书：" + bookData.name + "  序号为："+bookData.id );
                        exit = true;
                    }
                }

                if(exit == false) {
                    System.out.println("您要的图书不存在！");
                }

            }
            // 找id
            else if (checkStatus == 2) {
                System.out.print("请输入图书序号(id)：");
                Scanner scan = new Scanner(System.in); // 使用者輸入 1 or 2 or other number
                int numId = scan.nextInt();
                for (Book bookData : books) {
                    if(numId == bookData.id) {
                        System.out.println( "找到图书：" + bookData.name + "  序号为："+bookData.id );
                        exit = true;
                    }
                }
                if(exit == false) {
                    System.out.println("您要的图书不存在！");
                }
            }

            System.out.println("请问是否继续查书？1-是 2-否");
            int continueOrNot = 0;
            while(true){
                continueOrNot = systemCheckCallack();

                if(continueOrNot != 1 && continueOrNot != 2) {
                    System.out.println("命令错误，请重新输入！");
                } else {
                    break;
                }
            }
            if(continueOrNot == 2) {
                System.out.println("感谢您的使用，再见！");
                break;
            }
        }

    }   

    // 使用者輸入內容
    public static int systemCheckCallack () {
        Scanner scan = new Scanner(System.in);

        while(true) {
            try {
                // next()      字串(不包含空白字元、空白鍵、Tab)
                // nextInt()   整數 
                // nextFloat() 取得使用者輸入的浮點數
                // nextLine()  使用者輸入的字串(包含空白字元、空白鍵、Tab)
                int num = scan.nextInt(); 
                return num;
            } catch(InputMismatchException e) {
                System.out.println("请根据提示输入数字命令！");
                scan.next();
//                throw e;
            }
        }

    }

}

package imooc_homework;

public class Book {
    public String name;
    public int id;


    public Book(String name, int id){
        this.name = name;
        this.id = id;
    };

}

How to do

经验·与总结

自定义异常

java中的异常抛出

处理异常0

处理异常方法

检查异常0

Exception

00001

Throwable

package com.stx.librarySystem;

import com.stx.Test.Demo2;

import java.util.ArrayList;
import java.util.List;
import java.util.Scanner;

public class library {
    public int input(){
        System.out.println("输入命令：1-按照名称查找图书；2-按照序号查找图书；");
        Scanner in = new Scanner(System.in);
        int i=0;
        try{
            i=in.nextInt();
            return i;
        }catch (Exception e){
            System.out.println("命令输入错误！请根据提示重新输入数字命令！");
            return -1;
        }
    }
    public static void main(String[] args) {
        List<String> list=new ArrayList<String>();
        list.add("数据结构");
        list.add("高数");
        list.add("化学");
        list.add("物理");
//        list.forEach((e)->{
//            System.out.println(e);
//        });
        library lib = new library();
        int i=lib.input();
        while (i==-1){
            i=lib.input();
        }

        if (i==1){
            System.out.println("输入图书名称：");
            Scanner in = new Scanner(System.in);
            String bookname=in.next();
            int rs=list.indexOf(bookname);
            if (rs==-1){
                try {
                    throw new Demo2("图书不存在！");
                } catch (Demo2 demo2) {
                    demo2.printStackTrace();
                }
            }else {
                System.out.println("book:"+list.get(rs));
            }
        }else if (i==2){
            System.out.println("输入图书序号：");
            Scanner in = new Scanner(System.in);
            int bookid=in.nextInt();
            if (bookid>list.size()){
                try {
                    throw new Demo2("图书不存在！");
                } catch (Demo2 demo2) {
                    demo2.printStackTrace();
                }
            }else{
                System.out.println("book:"+list.get(bookid-1));
            }
        }
    }
}

模拟借书系统代码，仅供参考！

import java.text.SimpleDateFormat;
import java.util.Calendar;
import java.util.Date;
public class HelloWorld {
    
    public static void main(String[] args) {
// 创建Calendar对象
Calendar c = Calendar.getInstance();
        
// 将Calendar对象转换为Date对象
Date date = c.getTime();
        
// 创建SimpleDateFormat对象，指定目标格式
SimpleDateFormat sdf = new SimpleDateFormat("yyyy-MM-dd HH:mm:ss");
        
// 将日期转换为指定格式的字符串
String now = sdf.format(date);
System.out.println("当前时间：" + now);
}
}