为什么在捕捉到异常后调用findways(book)会出错

package findbook;
import java.util.InputMismatchException;
import java.util.Scanner;
public class Find {

    public static void main(String[] args) throws Nobook {
        // TODO 自动生成的方法存根
        String[] book= {"高数","英语","JAVA","信号"};
        Find book1=new Find();
        book1.findways(book);
    }
    //查找方法
    public void findways(String[] book) throws Nobook{
        Scanner in=new Scanner(System.in);
        try {
            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");
            int a=in.nextInt();
            switch(a) {
            case 1:
                findname(book);
                break;
            case 2:
                findnumber(book);
                break;
                
            }
            in.close();
        }catch(InputMismatchException e) {
            System.out.println("请输入整数！！！");
            findways(book);
        }
    }
    //按书名查找
    public void findname(String[] book) throws Nobook{
        Scanner in=new Scanner(System.in);
            System.out.println("输入图书名称：");
            String a=in.nextLine();
            boolean flag=false;
            try {
            for(int i=0;i<book.length;i++) {
                if(a.equals(book[i])) {
                    System.out.println("book:"+book[i]);
                    flag=true;
                    break;
                }
            }
            in.close();
            if(!flag) {
                throw new Nobook();
            }
            }catch(Nobook e){    
                findways(book);
            }
    }
    //按序号查找
    public void findnumber(String[] book) throws Nobook{
        Scanner in=new Scanner(System.in);
            System.out.println("输入图书序号：");
            int a=in.nextInt();
            boolean flag=false;
            try {
            for(int i=0;i<book.length;i++) {
                if(a==i) {
                    System.out.println("book:"+book[i]);
                    flag=true;
                    break;
                }
            }
            in.close();
            if(!flag) {
                throw new Nobook();
            }
            }catch(InputMismatchException e) {
                System.out.println("请输入整数！！！");
                findways(book);
            }catch(Nobook e) {
                System.out.println(e.getMessage());
                findways(book);
            }
    }
}

//自定义异常
package findbook;

public class Nobook extends Exception{
    public Nobook(){
        System.out.println("图书不存在！");
    }
}