课后小程序

1.

//信1605-3班  20163429  刘瑞欣
package Yichang;
import java.util.*;

class AException extends Exception
{
    String a;
    AException()  
    {
        a="输入有误";   
    }
    public String toString()
    {
        return a;
    }
}
 
class Chengji 
{ 
    public static void main(String args[]) 
    { 
     while(1>0)
       {
         Scanner sc = new Scanner(System.in); 
         System.out.println("请输入考试成绩（0~100）："); 
        try 
        { 
            String s = sc.nextLine();     
            getnum(s); 
        } 
        catch (AException e) 
        { 
            System.out.println(e.toString()); 
        } 
       }
    } 

    private static void getnum(String s) throws AException 
    { 
        for (int i = s.length()-1; i >= 0;i--) 
           {
            int chr = s.charAt(i);
          if (chr < 48 || chr > 57)
          {

              throw new AException(); 

          }
        }  
        double num = Double.parseDouble(s);   
        if (num < 0 || num> 100) 
        { 
            throw new AException(); 
        } 
        if (num>= 0 && num< 60)
        { 
            System.out.print("不及格
"); 
        } 
        else if (num >= 60 && num <= 70) 
        { 
            System.out.print("及格
"); 
        } 
        else if (num>= 70 && num<= 80) 
        { 
            System.out.print("中
"); 
        }
        else if (num >= 80 && num <= 90) 
        { 
            System.out.print("良
"); 
        } 
        else 
        { 
            System.out.print("优
"); 
        } 
    } 
}

3.

直接输入回车就崩溃了。其他都不会崩溃。