• 定义了三个类
• ErrorCodeException.java

public class ErrorCodeException extends Exception {

    public ErrorCodeException(){
    }

    public ErrorCodeException(String message){
        super(message);
    }
}

• NoExitBookException.java

public class NoExitBookException extends Exception {

    public NoExitBookException() {
    }

    public NoExitBookException(String message) {
        super(message);
    }
}

• BorrowBookSystem.java

public class BorrowBookSystem {

    String[] library = {"Java", "Python", "javascript", "Android", "iOS", "Linux", "Unix", "C", "C++", "C#", "Ruby", "Django", "Flask"};

    public static void main(String[] args) {
        BorrowBookSystem system = new BorrowBookSystem();
        system.borrow();
    }

    public void borrow() {
        while (true) {
            int command = 0;
            try {
                command = command();
            } catch (ErrorCodeException e) {
                System.out.println(e.getMessage());
            }
            if (command == 1) {
                try {
                    queryBookName();
                } catch (NoExitBookException e) {
                    System.out.println(e.getMessage());
                }
            } else if (command == 2) {
                try {
                    queryBookCode();
                } catch (ErrorCodeException e) {
                    System.out.println(e.getMessage());
                } catch (NoExitBookException e) {
                    System.out.println(e.getMessage());
                }
            }

        }
    }

    public int command() throws ErrorCodeException {
        int result;
        System.out.println("输入查询命令：1-按照图书名称查询，2-按照图书序列号查询。");
        Scanner scanner = new Scanner(System.in);
        String command = scanner.next().trim();
        if (command.equals("1")) {
            result = 1;
        } else if (command.equals("2")) {
            result = 2;
        } else {
            throw new ErrorCodeException("命令输入错误！请根据提示输入数字命令！");
        }
        return result;
    }

    private void queryBookCode() throws ErrorCodeException, NoExitBookException {
        System.out.println("输入图书序列号：");
        Scanner scanner = new Scanner(System.in);
        String next = scanner.next().trim();
        int number;
        try {
            number = Integer.parseInt(next);
        } catch (Exception e) {
            throw new ErrorCodeException("命令输入错误！请根据提示输入数字命令！");
        }
        try {
            String bookName = library[number];
            System.out.println("book:" + bookName);
        } catch (Exception e) {
            throw new ErrorCodeException("图书不存在!");
        }
    }

    private void queryBookName() throws NoExitBookException {
        System.out.println("输入图书名称：");
        Scanner scanner = new Scanner(System.in);
        String next = scanner.next().trim();
        boolean result = false;
        for (int i = 0; i < library.length; i++) {
            if (library[i].equals(next)) {
                System.out.println("book:" + library[i]);
                result = true;
                break;
            }
        }
        if (!result) {
            throw new NoExitBookException("图书不存在!");
        }
    }
}