Java入门第三季 借书系统异常

Book.java

package RentBook;

public class Book {
    String name;
    int id;

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

CommandException.java

package RentBook;

public class CommandException extends Exception {
    public CommandException() {

    }

    public CommandException(String e) {
        super(e);
    }
}

NotFoundException.java

package RentBook;

public class NotFoundException extends Exception {
    public NotFoundException() {

    }

    public NotFoundException(String e) {
        super(e);
    }
}

Main.java

package RentBook;

import java.util.Scanner;

public class Main {
    public void Solve() throws CommandException, NotFoundException {
        Scanner scan = new Scanner(System.in);
        Book[] books = {
            new Book(1, "maths"),
            new Book(2, "biology"),
            new Book(3, "history"),
            new Book(4, "computer")
        };
        System.out.println("请选择查询方式：1.按序号查询  2.按书名查询");
        int cas = scan.nextInt();
        if(cas == 1) {
            System.out.println("请输入书籍序号");
            int cur = scan.nextInt();
            if(cur < 1 || cur > 4) {
                throw new NotFoundException("图书不存在异常,请重新输入");
            } else {
                for(Book book : books) {
                    if(book.id == cur) {
                        System.out.println("book: " + book.name);
                        break;
                    }
                }
            }
        } else if(cas == 2) {
            System.out.println("请输入书籍名称");
            String cur = scan.next();
            boolean flag = false;
            for(Book book : books) {
                if(book.name.equals(cur)) {
                    System.out.println("book: " + book.name);
                    flag = true;
                    break;
                }
            }
            if(flag == false) {
                throw new NotFoundException("图书不存在异常,请重新输入");
            }
        } else {
            throw new CommandException("错误命令异常,请重新输入");
        }
    }

    public static void main(String[] args) {
        Main main = new Main();
        try {
            main.Solve();
        } catch(CommandException e) {
            e.printStackTrace();
        } catch(NotFoundException e) {
            e.printStackTrace();
        }
    }
}

请选择查询方式：1.按序号查询  2.按书名查询
2
请输入书籍名称
chinese
RentBook.NotFoundException: 图书不存在异常,请重新输入
    at RentBook.Main.Solve(Main.java:41)
    at RentBook.Main.main(Main.java:51)

请选择查询方式：1.按序号查询  2.按书名查询
3
RentBook.CommandException: 错误命令异常,请重新输入
    at RentBook.Main.Solve(Main.java:44)
    at RentBook.Main.main(Main.java:51)

请选择查询方式：1.按序号查询  2.按书名查询
1
请输入书籍序号
5
RentBook.NotFoundException: 图书不存在异常,请重新输入
    at RentBook.Main.Solve(Main.java:20)
    at RentBook.Main.main(Main.java:51)