新手写代码，可能比较繁复

public class book {

public static void main(String[] args) throws book_dontexist, error_command

{

book book1=new book();

book1.borrow_book1();

}

public  void borrow_book1() throws book_dontexist, error_command

{

//book book1 = new book();

System.out.println("1-按照名称查找图书；2-按照序号查找图书");

Scanner input=new Scanner(System.in);

int  command=input.nextInt();

if(command!=1&&command!=2)

{

try {

        throw new error_command("命令输入错误！请根据提示输入命令");

         }

    catch(error_command m) {

    }

    finally {

    borrow_book1();

    }

}

String[] library ={"小王子","玻璃城堡","悲惨世界","心理罪","杀死一只知更鸟"};

if(command==1)

{

   System.out.println("输入图书名称");

   int m=0;

   Scanner input1=new Scanner(System.in);

   String bookname=input1.next();

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

       {

       if(bookname.contentEquals(library[i]))

    {

   m++;

   System.out.println("book:"+bookname);// System.out.println(library[i]);

    } 

         if((i==library.length-1)&&(m==0))

         {

        try {

        throw new book_dontexist("图书不存在");

         }

    catch(book_dontexist e) {

    }

    finally {

    borrow_book1();

    }

         }

       }

}

if(command==2)

{

   System.out.println("输入图书序号");

   int m=0;

   Scanner input2=new Scanner(System.in);

   int  num=input2.nextInt();

       if(num<library.length)

    {

   System.out.println("book:"+library[num]);// System.out.println(library[i]);

    } 

       else 

         {

    try {

        throw new book_dontexist("图书不存在");

         }

    catch(book_dontexist e) {

    }

    finally {

    borrow_book1();

    }

         }

}

  }

}