异常流

import javax.swing.JOptionPane;

public class Grade {

 public static void main(String[] args){
  for(;;){
   boolean p;
      try{
         String str;
         str=JOptionPane.showInputDialog("请输入考试成绩（整数）：");
         int s;
         s=Integer.parseInt(str);
         if(s<0||s>100)
         {
          JOptionPane.showMessageDialog(
            null,"输入的成绩超出范围，请重新输入！");
          p=false;
         }
         else
         {
         if(s>=0&&s<60)
         {
          JOptionPane.showMessageDialog(
            null,"不及格！");

         }
         else if(s>=60&&s<70)
         {
          JOptionPane.showMessageDialog(
            null,"及格！");
         }
         else if(s>=70&&s<80)
         {
          JOptionPane.showMessageDialog(
            null,"中！");
         }
         else if(s>=80&&s<90)
         {
          JOptionPane.showMessageDialog(
            null,"良！");
         }
         else if(s>=90&&s<=100)
         {
          JOptionPane.showMessageDialog(
            null,"优！");
         }
         p=true;
        }
      }
      catch(NumberFormatException e){
         JOptionPane.showMessageDialog(
           null,"输入必须为整数！");
         p=false;
        }
      if(p)
       break;
       }
      }
}