方法不改变main中的数组

Question

第一次发布在这里,但我有一个问题,关于一个方法没有改变它给出的数组中的值.

我认为数组是通过引用传递的,因此更改方法中的数组会在数组中更改它.然而,这对我不起作用,我不知道为什么.

我的代码如下.不起作用的方法是readFile()

package StudentsGrades;

import java.io.*;
import java.lang.*;

public class StudentsGrades {

    public static void main(String [] args ) {
    int numberOfLines = 0;
    String fileName = "";

    fileName = "marks_file.csv";
    //Obtain the number of lines in the given csv.
    numberOfLines = getNumberLines(fileName);
    System.out.println(numberOfLines);

    //initialise the arrays that the data will be stored in.
    double[] gradesArray = new double[numberOfLines];
    String[] studentsArray = new String[numberOfLines];

    if (numberOfLines > 0) {
        readFile(studentsArray, gradesArray, numberOfLines, fileName);
    }
    System.out.println(studentsArray[4]);
}
public static int getNumberLines (String importFile)  {
    int numLines = 0;
    try {
        FileReader fnol = new FileReader(importFile);
        LineNumberReader lnr = new LineNumberReader(fnol);

        while (lnr.readLine() != null ) {
            numLines++;
        }

    } catch (FileNotFoundException fe) {
        System.out.println("The file cannot be found");
    } catch (Exception e) {
        System.out.println("Invalid");
    }
    return numLines;
}
public static void readFile (String [] studentsArray, double[] gradesArray, int numLines, String fileName ) {
    try {
        String lineData = null;
        FileReader fr = new FileReader(fileName);
        BufferedReader br = new BufferedReader(fr);

        String currentLine = "";

        while ((currentLine = br.readLine()) != null ) {
            //Store the current Line in a string
            String[] lineDataArray = currentLine.split("\\s*,\\s*");
            //To index its position in the array
            int index = 0;
            //System.out.println(lineDataArray[1]);
            studentsArray[index] = lineDataArray[0];
            gradesArray[index] = Double.parseDouble(lineDataArray[1]);
            System.out.println("Student: " + studentsArray[index]
            + " Grade: " + gradesArray[index]);
            index++;
        }
    } catch (Exception e) {
        System.out.println("Unexpected value in file.");
    }

}
}

输出

学生:Christopher Lee年级:54.0学生:Stanley Wright年级:90.5学生:Oliver Stewart年级:75.8学生:Jessica Chang年级:34.65学生:Adam Bweon年级:66.6学生:Chrissy Yeo等级:88.9 null

正如您所看到的那样,最后一个值就是null当我尝试从数组中打印一个值时Main.

Answer 1

将int index=0;外循环.

如果要填充数组,则需要index在循环之前声明.从现在开始它就在循环内部,每次都重新声明它并初始化为0.因此,当你使用它时,index总是为0,并且你会覆盖这些值.