private static String getBookByNumber(String[] books)throws Exception{

System.out.println();

System.out.println("输入书的序号：");

 int num =input.nextInt();

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

    if (books[num-1].equals(books[i])){

    return books[i];

    }

    }throw new Exception("图书不存在！");

     }