Java的Eclipse的NullPointerException異常

Question

我聲明的變量和初始化，但我仍然得到這個錯誤

代碼：

//Main 

import java.util.Random; 
import java.util.Scanner; 

public class Main { 


public static void main(String[] args) 
{ 

// Scanner input=new Scanner(System.in); 
// Random rnd=new Random(); 
    StuInfo(); 

} 
public static void StuInfo() 
{ 
    Scanner io=new Scanner(System.in); 
    Random rnd=new Random();  
    System.out.println("How many students are there?"); 
    student[] stu = new student[io.nextInt()]; 
    for (int i = 0; i < stu.length; i++) 
    { 
     stu[i].age = 5; 

    } 
} 
} 

//Student 
public class student { 
    int age; 
    double[] grade; 
    String name; 

} 

輸入：

錯誤：

exception in thread "main" java.lang.NullPointerException

at Main.StuInfo(Main.java:39)

at Main.main(Main.java:12)

Answer 1

當你創建一個對象數組時，你的數組填充空值。所以首先在for循環中你應該定義stu [i] = new Student（）;那麼你可以寫stu [i] .age = 5;