java - 如何查找来自 csv 文件的数组列表的平均分(JAVA)

Question

我有一个 csv 文件，其中包含学生 ID、姓氏、名字、分数、电话号码等列表。我已将它们组织到一个数组列表中，以便当您调用 stu[100].mark 时它将在 csv 文件列表中找到第 100 个学生的分数。有学生1000人。我需要计算所有学生的总平均分(每个学生只有一个分数)我把它放在一个循环中，但它只是打印出他们的分数。如果您需要更多详细信息，我深表歉意。

这是代码:

公开课StudentRecs{

public static String user;
public int StuRec;
public static int numstu;
public static double average;
//public static StuRec[] stu;  
static StuRec[] stu = new StuRec[1000];

public static void main(String[] args) throws IOException {
    for (int i = 0; i < 1000; i++) {
        stu[i] = new StuRec();
    }
    StuRec stu = new StuRec();
    readFile(user);
    menu();
}
public static String filename;
Scanner reader = new Scanner(filename);

public static Boolean readFile(String filename) throws IOException { //Constructor for filename
    try {
        Scanner userInput = new Scanner(System.in);

        System.out.println("Type R To Read a File or Type Default for the default file");
        user = userInput.nextLine();
        if (user.equalsIgnoreCase("r")) {
            user = userInput.nextLine();
        }
        filename = user;
        if (user.equalsIgnoreCase("default")) {
            filename = "newreg2.csv";
        }


        Scanner input = new Scanner(new FileReader(filename));
        while (input.hasNext()) {
            in(input.nextLine());
            numstu++;
        }
        input.close();
        return true;

    } catch (IOException e) {
        System.err.println(e.getMessage());
    }
    return false;
}


public static void in(String reader) {
    String splitter[];
    splitter = reader.split(",");
    stu[numstu] = new StuRec();
    stu[numstu].studentID = splitter[0];
    stu[numstu].lastName = splitter[1];
    stu[numstu].firstName = splitter[2];
    stu[numstu].phoneNumber = splitter[3];
    stu[numstu].courseCode = splitter[4];
    stu[numstu].periodNumber = Integer.parseInt(splitter[5]);  // parseInt turns a string of digits into an integer
    stu[numstu].mark = Integer.parseInt(splitter[6]);
}

public static boolean menu() {
    int total = 0;
    String choice;
    Scanner userInput = new Scanner(System.in);
    System.out.println("=============================================");
    System.out.println("Type R To Read Another File");
    System.out.println("Type L To Print all File Records");
    System.out.println("Type AA To Print The Average Of All The Marks");
    choice = userInput.nextLine();
    for (int i = 0; i < numstu; i++) {
        if (choice.equalsIgnoreCase("L")) {
           System.out.println(stu[i].lastName + ", " + stu[i].firstName + ", " + stu[i].studentID + ", " + stu[i].phoneNumber + ", " + stu[i].courseCode + ", " + stu[i].periodNumber + ", " + stu[i].mark);
        }else if (choice.equalsIgnoreCase("R")){

        } else if (choice.equalsIgnoreCase("AA")) {
               total = total + stu[i].mark;

        } else {
            System.err.println("Unknown Key Try Again...");

        }

  average = total / 1000;  // compute the average.
     System.out.println(average);    

    } return menu();

} }

Answer 1

您的平均例程计算不正确。它只是取第 n 个标记并将其添加到自身，除以 1000。由于您使用的是整数，因此它只会向下舍入，有效地为您提供每次迭代的平均值第 n 个标记 + 0，从而为您留下循环完成的最后一个标记。

您需要继续添加平均值，完成后除以 1000 即可得到值。

public static boolean menu() {
    String choice;
    Scanner userInput = new Scanner(System.in);
    System.out.println("=============================================");
    System.out.println("Type R To Read Another File");
    System.out.println("Type L To Print all File Records");
    System.out.println("Type AA To Print The Average Of All The Marks");
    choice = userInput.nextLine();

    for (int i = 0; i < numstu; i++) {
        if (choice.equalsIgnoreCase("L")) {
           System.out.println(stu[i].lastName + ", " + stu[i].firstName + ", " + stu[i].studentID + ", " + stu[i].phoneNumber + ", " + stu[i].courseCode + ", " + stu[i].periodNumber + ", " + stu[i].mark);
        }else if (choice.equalsIgnoreCase("R")){

        } else if (choice.equalsIgnoreCase("AA")) {
              average += stu[i].mark; // keep adding to average

        } else {
            System.err.println("Unknown Key Try Again...");

        }
    } 
    // divide by zero protection
    if ( numstu > 0 ) {
        average = average/numstu;  // compute the average. Always use the size in terms of a variable whenever possible.
        System.out.println(average); // as noted below, if this is an integer value, < #of students computations will eval to 0.
                                     // might be better to use double
    }
    else {
        System.out.println("Oops! No students! :(");
    }
    return menu();
}

请注意，您的菜单效率有点低，但手头的问题应该可以解决。