从另一个方法显示 Arraylist

Question

我在这里遇到的问题是我想在一个单独的文件中输出三个学生分数的字母等级，格式为：

name1   score1
name2   score2
name3    score3

在乐谱和姓名之间有制表符。

我在这里面临的问题是，如果您向下滚动到我的 toString2 方法，我将运行我的程序，它应该接受三个分数并根据我的计算输出正确的字母等级。相反，我的程序进入了一个不受控制的循环并以 [] 结束。我该如何解决这个问题？

 package file;

 import java.io.File;
 import java.io.FileNotFoundException;
import java.util.ArrayList;
import java.util.Scanner;

 public class ReadData2 
{
ArrayList<String> name = new ArrayList<String>();
ArrayList<Double> score  = new ArrayList<Double>();
ArrayList<String> lettergrade = new ArrayList<String>();
double mean;
double std;

public ReadData2()
{
    mean= 0;
    std=0;
}
public  void readData(File file) throws FileNotFoundException 
{
    //File file = new File("data.txt");
    Scanner scanner = new Scanner(file);
    int l = 0;


    while (scanner.hasNextLine()) { 
        String line = scanner.nextLine();
        String [] words = line.split("\t"); 
        name.add(words[0]); 
        score.add(Double.parseDouble(words[1]));
    }
}

public String toString()
{

    StringBuilder out = new StringBuilder();
    for(String n: name)
    {
        out.append(n);
        out.append("\n");

    }
    for(double n: score)
    {
        out.append(n);
        out.append("\n");   
    }
    return out.toString();      
}   

public double fndMean()
{
    double mean  = 0;
    double sum = 0;
    for(Double n: score)
    {
        sum= sum+n; 
    }
    mean= sum/score.size();
    return mean;
}

public double fndStandard()
{
    double sumOfDifferences = 0;
    double mean = fndMean();
    for(Double n: score)
    {
        sumOfDifferences += Math.pow((n- mean),2);  
    }
    double temp = sumOfDifferences/ score.size();
    return Math.sqrt(temp);
}
public  ArrayList<String>  toString2(File file) throws FileNotFoundException
{
    StringBuilder grades = new StringBuilder();
    double mean1 = fndMean();
    double std1 = fndStandard();

    Scanner scanner = new Scanner(file);
    int l = 0;

    while (scanner.hasNextLine()) { 
        String line = scanner.nextLine();
        String [] words = line.split("\t"); 
        name.add(words[0]); 
        score.add(Double.parseDouble(words[1]));

        for(double n: score)
        {
            grades.append(n);
            grades.append("\n");    
        }


        for(int i = 0; i < ((score.size())) && i < name.size(); i++)
        {
            if(mean1 +std1 < score.get(i))
            {
                System.out.println("A");
            }
            else if( (score.get(i) >= mean1+(std1/3)) &&  (mean1 +std1)> score.get(i))
            {
                System.out.println("B");
            }
            else if( (score.get(i) >= mean1-(std1/3)) &&  (mean1 +(std1/3))> score.get(i))
            {
                System.out.println("C");

            }
            else if( (score.get(i) >= mean1-(std1)) &&  (mean -(std1/3))> score.get(i))
            {
                System.out.println("D");
            }   
            else if(mean1 - std1 > score.get(i))
            {
                System.out.println("F");
            }

        }
    }
    return lettergrade;
}
}

Answer 1

相反，我的程序进入了一个不受控制的循环，并以 []。我该如何解决这个问题？

你得到一个空的 [] 因为你并没有真正修改你的“字母等级”数组。您只是将成绩打印到控制台，而不是真正将其添加到数组中。除了 sysout 语句之外，您还需要将成绩添加到数组中。例如

lettergrade.add("B");