输出给我一个 NaN ，为什么？ [ 完全的 ]

Question

我试图通过一个方法传递一个数组列表，我想显示它。这是我的代码

        public static void dispArrayList(ArrayList<Float> arr) {
        
        ArrayList<Float> ssGrades = new ArrayList<Float>();
    
        float ss = 0, data = 0, sum = 0, avg = 0;
        
        for (int i= 0; i < ssGrade.size(); i++)
        {
            data = ssGrades.get(intIndex);
            sum += fltData;
            System.out.println(fdata);
        }  
        
        avg = sum/ ssGrades.size();
        System.out.println("\nAverage is " + avg+ ".");     
    }
}

问题是我的输出给出的是 NaN 而不是计算平均分，为什么会这样？我该如何解决？

Answer 1

显示方法中无需创建新的ArrayList
改用传递的数组 arr
也永远不要像那样初始化一堆变量

 public static void main(String[] args)
{

    Scanner objDataEntry = new Scanner(System.in);

    ArrayList<Float> objGrades = new ArrayList<Float>();
    float fltGrade = 0, fltData = 0, fltSum = 0, fltAverage = 0;


    System.out.println("Enter a grade, -1 to exit..");
    while (fltGrade >= 0)
    {
        System.out.print("Grade: ");
        fltGrade = objDataEntry.nextFloat();

        if (fltGrade >= 0)
        {
            objGrades.add(fltGrade);
        }
    }
    dispArrayList(objGrades);
}


public static void dispArrayList(ArrayList<Float> arr) {
    float fltGrade = 0, fltData = 0, fltSum = 0, fltAverage = 0;
    
    System.out.println("\n\nGenerating grade listing");
    System.out.println("---------------------------");
    for (int intIndex = 0; intIndex < arr.size(); intIndex++)
    {
        fltData = arr.get(intIndex);
        fltSum += fltData;
        System.out.println(fltData);
    }

    fltAverage = fltSum / arr.size();
    System.out.println("\nAverage is " + fltAverage + ".");

}

另外，你有很多你不需要的无用变量
修改后的代码：

 public static void main(String[] args)
{

    Scanner objDataEntry = new Scanner(System.in);

    ArrayList<Float> objGrades = new ArrayList<Float>();
    float fltGrade = 0;


    System.out.println("Enter a grade, -1 to exit..");
    while (fltGrade >= 0)
    {
        System.out.print("Grade: ");
        fltGrade = objDataEntry.nextFloat();

        if (fltGrade >= 0)
        {
            objGrades.add(fltGrade);
        }
    }
    dispArrayList(objGrades);
}


public static void dispArrayList(ArrayList<Float> arr) {
    float fltSum = 0, fltAverage = 0;

    System.out.println("\n\nGenerating grade listing");
    System.out.println("---------------------------");
    for (int intIndex = 0; intIndex < arr.size(); intIndex++)
    {
        fltSum += arr.get(intIndex);
        System.out.println(arr.get(intIndex));
    }

    fltAverage = fltSum / arr.size();
    System.out.println("\nAverage is " + fltAverage + ".");

}

Answer 2

您没有使用 ArrayList 传递给 dispArrayList 方法。

在 dispArrayList 方法中删除这一行 ArrayList objGrades = new ArrayList();

把这个public static void dispArrayList(ArrayList arr)改成public static void dispArrayList(ArrayList objGrades)

Answer 3

我认为fltSum 和objGrades.size() 都是0。

ZERO / ZERO = NaN

您可以参考这个链接：https://www.baeldung.com/java-not-a-number

Answer 4

基本上你没有使用方法dispArrayList(ArrayList arr)中传递的参数
并除以零。

Answer 5

如果读取的值不是有效的浮点数，Scanner#nextFloat() 可以返回 NaN。

一旦列表中有一个 NaN 值，所有值的总和也将是 NaN。

此外，您不会在 dispArrayList(ArrayList<Float> arr) 方法中循环遍历 arr 列表，而是遍历空的 ArrayList<Float> objGrades，因此以下行将计算为 NaN，因为除以零：

fltAverage = fltSum / objGrades.size();
// fltAverage = 0.0f / 0.0f

Answer 6

在dispArrayList(ArrayList<Float> arr) 方法中，而不是使用arr 数组参数，您定义了一个空的新数组并对其进行迭代，您必须按如下方式对其进行更改才能正常工作，其次我将强制转换添加到fltAverage = (float)fltSum / arr.size(); 的强制转换值浮动所以要精确。

public static void dispArrayList(ArrayList<Float> arr) {
        float fltGrade, fltData, fltSum, fltAverage;
        fltGrade = fltData = fltSum = fltAverage = 0;
        
        System.out.println("\n\nGenerating grade listing");
        System.out.println("---------------------------");
        for (int intIndex = 0; intIndex < arr.size(); intIndex++) {
            fltData = arr.get(intIndex);
            fltSum += fltData;
            System.out.println(fltData);
        }

        fltAverage = (float)fltSum / arr.size();
        System.out.println("\nAverage is " + fltAverage + ".");
    }

完整代码：

import java.util.ArrayList;
import java.util.Scanner;

public class Grades {

    public static void main(String[] args) {

        Scanner objDataEntry = new Scanner(System.in);

        ArrayList<Float> objGrades = new ArrayList<Float>();
        float fltGrade, fltData, fltSum, fltAverage;
        fltGrade = fltData = fltSum = fltAverage = 0;

        System.out.println("Enter a grade, -1 to exit..");
        while (fltGrade >= 0) {
            System.out.print("Grade: ");
            fltGrade = objDataEntry.nextFloat();

            if (fltGrade >= 0) {
                objGrades.add(fltGrade);
            }
        }
        dispArrayList(objGrades);
    }

    public static void dispArrayList(ArrayList<Float> arr) {
        float fltGrade, fltData, fltSum, fltAverage;
        fltGrade = fltData = fltSum = fltAverage = 0;
        
        System.out.println("\n\nGenerating grade listing");
        System.out.println("---------------------------");
        for (int intIndex = 0; intIndex < arr.size(); intIndex++) {
            fltData = arr.get(intIndex);
            fltSum += fltData;
            System.out.println(fltData);
        }

        fltAverage = (float)fltSum / arr.size();
        System.out.println("\nAverage is " + fltAverage + ".");
    }
}