java - 尝试解析数组时出现空指针异常(java)

Question

当我尝试解析字符串数组索引时，出现空指针异常。我该如何解决？谢谢

public class studentclass {
public static void main(String[] args){

    Scanner scan = new Scanner(System.in);
    String[][] student = new String[10][];
    Double[][] results = new Double[10][];
    Double[] total = new Double[10];
    String tableln = "";

   for(int index = 0; index < student.length; index++){
    System.out.println("\nPlease enter student " + (index+1) + "'s details");
    String userinput = scan.nextLine();
    student[index] = userinput.split(",");

    //converts string array in to double array but receiving null pointer exception
    results[index][0] = Double.parseDouble(student[index][2]); 
    results[index][1] = Double.parseDouble(student[index][3]);
    results[index][2] = Double.parseDouble(student[index][4]);
    results[index][3] = Double.parseDouble(student[index][5]);
    total[index] = (results[index][0]*0.1+results[index][1]*0.4+
                    results[index][2]*0.3+results[index][3]*0.2);

Answer 1

看起来results[index]需要初始化。您使用 new 为 results[0..n] 分配了内存，但没有为 results[index][0...n] 分配了内存。

如果您始终存储四个值，请添加如下内容:

results[index] = new Double[4];