请大神多多指教，有哪里可以更加完善

package bookStroe;

import java.util.Scanner;

public class BS {

         public static void main(String[] args){

         String[][] book = {{"1","论语"},{"2","数据库"},{"3","建模"}};    //初始化书店的书

         while(true) {    //无限循环查书

                 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 num=new Scanner(System.in).nextInt();

                     if(num!=1&&num!=2) {       //只有1，2两个选项，输入其他命令均抛出异常

                         throw new ClassCastException("命令输入错误！请根据提示输入数字命令！"); 

                     }

                     String bName=null;        //定义一个空指针

                     if(num==1) {

                         System.out.println("图书名称：");

                         String name=new Scanner(System.in).nextLine();

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

                              if(name.equals(book[i][1])) {

                                  bName="book："+book[i][1];        //有找到书就赋值给先前定义的空指针

                                  break;        //停止查书系统

                              }

                          }

                     System.out.println(bName.toString());        //引用，如果bName为空则抛出异常

                     break;        //退出查书系统

                 }

                 if(num==2) {

                     System.out.println("图书序号：");

                     int mark=new Scanner(System.in).nextInt();

                     System.out.println("book："+book[mark-1][1]);

                     break;        //退出查书系统

                 }

             }catch(NullPointerException e) {

                 System.out.println("图书不存在");            //空指针异常

             }catch(ArrayIndexOutOfBoundsException e) {

                 System.out.println("没那么多本书");        //数组溢出异常

             }catch(Exception e) {

                 System.out.println("命令输入错误！请根据提示输入数字命令！");        //其他异常

             }

         }

     }

}