java入门第三季--借书系统

package borrowbook;
public class BorrowBook {
    public static void main(String[] args) {
        Choose cs = new Choose();
        cs.runChoose();
    }   
}

package borrowbook;
import java.util.Scanner;

public class Choose {
    private String str;
    private int choice;
    String[] book;
public Choose() {
        this.book = new String[]{"gaoshu", "sjjg", "mg", "English"};
    }
public void doChoiceRight()throws Exception{
        if(choice > 3 || choice < 1){
            throw new Exception("命令输入错误！请根据提示输入数字命令！");
        }
    }

   public void FindBookExist()throws Exception{
        for(int i=0 ; i < book.length;i++)
        {

                if(str.equalsIgnoreCase(book[i])){
                    System.out.println("book:"+ book[i]);
                    return;
                }
        }
        throw new Exception("图书不存在！");
    }

    public void isNumberExist()throws Exception{
        if(choice > book.length || choice < 1){
            throw new Exception("序号不存在！");
        }else{
            System.out.println("book:"+ book[choice-1]);
        }

    }

    public void runChoose(){
    while(true){

       System.out.println("输入命令：1-按照书名查找图书"+
                " 2-按照序号查找图书"+"3-退出");
       //判断输入的命令是不是数字
       try{
            Scanner input = new Scanner(System.in);
            choice = input.nextInt();
            doChoiceRight();
        }catch(Exception e){
            System.out.println("命令输入错误！请根据提示输入数字命令！");
            continue;
        }
        //判断输入的数字是否有相应的选项
        try{
            doChoiceRight();
        }catch(Exception e){
            System.out.println(e.getMessage());
            continue;
        }
        //choice保存正确的输入命令，判断choice
       if(choice == 1){
           System.out.println("输入图书名：");
           Scanner input = new Scanner(System.in);
           str = input.next();

           try{
               FindBookExist();
        }catch(Exception e){
            System.out.println(e.getMessage());

        }

       }else if(choice == 2){
           System.out.println("输入图书序号：");
           Scanner input = new Scanner(System.in);
           try{
               choice = input.nextInt();
           }catch(Exception e){
               System.out.println("命令输入错误！");
               continue;
           }

           try{
               isNumberExist();
            }catch(Exception e){
            System.out.println(e.getMessage());
           }

       }else if(choice ==3 ){
           return;
       }

    }
    }

}