从Txt中读取整数并总结它

Question

你要写一个程序来计算考试成绩列表的统计数据，考试统计程序(ESP)。输入是一个文本文件的名称，该文件包含分数数和分数列表。(参见下面的例子。)然后，您应该显示以下信息:

。分数的数量
b.最低、最高和平均分数
c. a、b、c、d、f的个数，采用90-80-70-60分制。

我的问题是:我不知道如何让变量grade取数字。

当我运行这个程序时，它给了我这个错误:

Exception in thread "main" java.util.NoSuchElementException
     at java.util.Scanner.throwFor(Unknown Source)
     at java.util.Scanner.next(Unknown Source)
     at java.util.Scanner.nextInt(Unknown Source)
     at java.util.Scanner.nextInt(Unknown Source)
     at IntegersFromFile.main(IntegersFromFile.java:60)

下面是我的代码:

import java.io.File;
import java.io.FileNotFoundException;
import java.util.ArrayList;
import java.util.Scanner;
public class IntegersFromFile 
{
    public static void main(String[] args) 
        {
        Scanner file = null;
        int grade = 0;
        int min = 100;
        int max = 0;
        ArrayList<Integer> grades = new ArrayList<Integer>();
        int a, b, c, d, f;
        a = 0;
        b = 0;
        c = 0;
        d = 0;
        f = 0;
        double aA, aB, aC, aD, aF;
        aA = 0;
        aB = 0;
        aC = 0;
        aD = 0;
        aF = 0;
        System.out.println("***Welcome to the Exam Statistics Program!!***");
        System.out.println("Please enter the name of your data file:");
        Scanner input = new Scanner(System.in);
        String file_name = input.nextLine();
        try 
            {
            file = new Scanner(new File(file_name));
            }
        catch (FileNotFoundException e) 
            {
            e.printStackTrace();
            }
        while (file.hasNext()) 
            {
            if (file.hasNextInt()) 
                {
                grades.add(file.nextInt());
                } 
            else
                file.next();
            }
        do 
            {
            grade = file.nextInt();
            if (grade >= 0) 
                {
                grades.add(grade);
                if (grade < 60) 
                    {
                    f++;
                    aF += grade;
                    } 
                else if (grade < 70) 
                    {
                    d++;
                    aD += grade;
                    } 
                else if (grade < 80) 
                    {
                    c++;
                    aC += grade;
                    } 
                else if (grade < 90) 
                    {
                    b++;
                    aB += grade;
                    } 
                else 
                    {
                    a++;
                    aA += grade;
                    }
                if (grade < min)
                    min = grade;
                if (grade > max)
                    max = grade;
                }
            } 
        while (grade >= 0);
        if (aA > 0)
            aA /= a;
        if (aB > 0)
            aB /= b;
        if (aC > 0)
            aC /= c;
        if (aD > 0)
            aD /= d;
        if (aF > 0)
            aF /= f;
        double avg = 0;
        for (int i = 0; i < grades.size(); i++) {
            avg += grades.get(i);
            }   
        avg /= grades.size();
        System.out.println("Total Number of Scores: " + grades.size());
        System.out.println("Total As: " + a);
        System.out.println("Total Bs: " + b);
        System.out.println("Total Cs: " + c);
        System.out.println("Total Ds: " + d);
        System.out.println("Total Fs: " + f);
        System.out.println("Average A: " + aA);
        System.out.println("Average B: " + aB);
        System.out.println("Average C: " + aC);
        System.out.println("Average D: " + aD);
        System.out.println("Average F: " + aF);
        System.out.println("The highest grade was " + max);
        System.out.println("The lowest grade was " + min);
        System.out.println("The average grade was " + avg);
    }
}

Answer 1

问题是，当程序执行到第60行时，扫描器的输入"耗尽"。在开始do- cycle之前，应该重新初始化file变量(建议将其重命名为scanner或类似的名称)。

不太确定应用程序的逻辑，特别是do-循环是否应该在while-循环内，但我建议你使用括号，即使控制结构只有一条语句。这样你可以更好地勾勒出你的意图，并减少出现难以发现的错误的可能性。