带有锯齿状数组的NullPointerException

Question

我无法查看导致错误的原因。代码低于和低于我收到的错误消息。谢谢。

import java.util.*;
import java.io.*;

public class IO {

public static void main(String[] args) throws Exception {
    File inFile = new File("src/passign6/grades.txt");
    File outFile = new File("src/passign6/finalgrades.txt");

    try (
            Scanner input = new Scanner(inFile);
            PrintWriter output = new PrintWriter(outFile);) {

        int[][] grades = new int[42][];
        for (int i = 0; input.hasNextLine() && i < grades.length; i++) {
            String line = input.nextLine();
            Scanner input2 = new Scanner(line);
            for (int j = 0; input2.hasNextInt() && j < grades[i].length; j++) {
                grades[i][j] = input.nextInt();
            }

            input.close();
            output.close();
        }

    }

}
}

Exception in thread "main" java.lang.NullPointerException
at io.IO.main(IO.java:20)