请大神看一下，错误是：a1 cannot be resolved to a variable。求解释一下哈

Question

package com.imooc;import java.util.Scanner; public class BorrowBook {    String[] shu={"高数","大学英语","计算机"};    Scanner sc = new Scanner(System.in); public void test1(){    System.out.println("输入命令1或2：1代表按照书名查找图书；2代表按照序号查找图书");} public void test2() throws Exception{    test1();    int a1=sc.nextInt();    if (a1!=1||a1!=2){     throw new Exception("命令输入错误；请根据提示输入数字命令！!");     }   }public void test3() {  try{      test2();    }catch(Exception e){    test3();}if(a1==1){    System.out.println("请输入图书名");    String a2=sc.next();    for(int i=0;i<3;i++){        if(a2==shu[i])            System.out.println("book:"+a2);    }}    else if(a1==2)    {        System.out.println("请输入图书序号");        int b2= sc.nextInt();        for(int i=0;i<3;i++){            if(b2==i)                System.out.println("book:"+shu[i]);    }    System.out.println("图书不存在");}}}