java - 在java中使用文件流时没有得到任何输出

Question

我已经在编程作业的这一部分上停留了一段时间，我似乎不明白出了什么问题。我应该使用扫描仪从输入文件中获取成绩并将其放入数组(而不是 ArrayList)中。然后它应该计算平均值、最大值和最小值，然后将它们打印到一个新的单独文本文件中。程序运行没有错误，但我的输出文件中没有任何输出。我是不是想太多了？请原谅代码困惑，我稍后会修复它。

import java.util.Scanner;
import java.io.*;
public class GradeStatistics {

public static void main(String[] args) throws FileNotFoundException {
    Scanner scanNum = new Scanner(new File("grades.txt"));
    double total = 0;
    int numStudents = 0;

    //traverse the file, counting the number of lines and save into numStudents
    while(scanNum.hasNextInt())
    {
        numStudents += 1;
    }

    int grades[] = new int[numStudents];    //create grades array

    Scanner scan2 = new Scanner("grades.txt");

    //populate the array
    for(int i = 0; i < grades.length; i++)
    {
        grades[i] = scan2.nextInt();
    }

    int max = grades[0];
    int min = grades[0];

    //find the max and min
    for(int i = 0; i < grades.length; i++)
    {
        total = total + grades[i];
        if(grades[i] > max)
        max = grades[i];
    }
    for(int i = 0; i < grades.length; i++)
    {
        if(grades[i] < min)
            min = grades[i];
    }
    double average = total / grades.length;     //calculate the average

    //create a new file "results.txt" to print our results
    FileOutputStream f = new FileOutputStream("results.txt");
    System.setOut(new PrintStream(f));
    System.out.printf("The average is: %.2f\n", average);
    System.out.println("The minimum is: " + min);
    System.out.println("The maximum is: " + max);
    scan2.close();
    scanNum.close();

}

}

Answer 1

这是一个无限循环，因为它不会推进文件指针:

while(scanNum.hasNextInt())
{
    numStudents += 1;
}

该行还包含一个错误:

Scanner scan2 = new Scanner("grades.txt");

应该是

Scanner scan2 = new Scanner(new File("grades.txt"));