这个java程序怎么改就可以运行了，为什么空指针异常

Question

import java.util.Scanner;

```...}
class Student{
    String name=" ";
    String sex=" ";
    float mathGrade=0;
    float xiandaiGrade=0;
    float cGrade=0;
    float javaGrade=0;
    public void average(){
        System.out.println("输出平均成绩");
        float grade=(mathGrade+xiandaiGrade+cGrade+javaGrade)/4;
     }
     public void outputMessage(){
         System.out.println("姓名"+name);
          System.out.println("性别"+sex);
      }
     public void input(){
         Scanner sa=new Scanner(System.in);
         mathGrade=sa.nextFloat();
         System.out.println("高数为"+mathGrade);
         Scanner sb=new Scanner(System.in);
         xiandaiGrade=sb.nextFloat();
         System.out.println("线代为"+xiandaiGrade);
         Scanner sd=new Scanner(System.in);
         cGrade=sd.nextFloat();
         System.out.println("c语言为"+cGrade);
         Scanner se=new Scanner(System.in);
         javaGrade=se.nextFloat();
         System.out.println("面向过程为"+javaGrade);
         Scanner sf=new Scanner(System.in);
         sex=sf.next ();
         System.out.println("性别为"+sex);
         Scanner sg=new Scanner(System.in);
         name=sg.next();
         System.out.println("姓名为"+name);
     } 
}
public class information{
    public static void main(String[] args){
        Student[] a=new Student[2];
        for(int i=0;i<=a.length;i++){
            a[i].input();
        }
        int m=0;
        while(m<2){
            Scanner sg=new Scanner(System.in);
             m=sg.nextInt();
            System.out.println("要查询的序号"+m);
            a[m].outputMessage();
            a[m].average();
        }
   }
}

Answer 1

因为你只是创建了对象数组,没有对数组内的每一个对象实例化
在for循环内添加实例化函数即可
有帮助望采纳~