Java-并行数组上的ArrayIndexOutOfBounds错误

Question

I'm having a bit of trouble with this project:

We're given a text file of 5 students, with 4 number grades following each name in a separate line. We have to use our main method to read the file, then perform calculations in the gradebook class. However, from what others in class have been saying the method we're using is archaic at best, involving Parallel arrays. We don't really seem to have any other option though, so I'm making due with what I can. But near what I'm hoping is the end of this code, I've encountered a problem, where it says the index that contains the grades for students is out of bounds.

I've rewritten the readFile method in my main in quite a few different ways, but no matter what I still get these errors. Could anyone help me understand what's going on? I'll post everything I can. I also apologize if I'm a bit slow/incapable with this, this is my first time coding java in months unfortunately.

Also, in the error I post, line 64 of the main class is: grades[test] = inputFile.nextDouble();

run:
Exception in thread "main" java.lang.ArrayIndexOutOfBoundsException: 4
    at Package1.GradeBookDemo.readFile(GradeBookDemo.java:64)
    at Package1.GradeBookDemo.main(GradeBookDemo.java:29)
Java Result: 1
BUILD SUCCESSFUL (total time: 0 seconds)

The following is my Main method:

import java.util.Scanner;
import java.io.*;

public class GradeBookDemo {

    public static void main(String[] args) throws IOException {

        // Create a new gradebook object
        Gradebook gradeBook = new Gradebook();

        //Read StudentInfo file for names and test scores using readFile method
        readFile(gradeBook);

        //Output Student data
        for (int index = 1; index <= 5; index++)
        {
            System.out.println("Name: " + gradeBook.getName(index) + 
                    "\tAverage Score: " + gradeBook.getAverage(index) +
                    "\tGrade: " + gradeBook.getLetterGrade(index));
        }

    }


    // This method reads from the StudentInfo file
    public static void readFile(Gradebook gradeBook) throws IOException
    {

        int nI = 0; // Name index
        int gI = 4; // Grade index

        // Create a string array to hold student names and another for grades
        double[] grades = new double[gI];

        // Access the StudentInfo text file
        File sFile = new File("StudentInfo.txt");
        // Create a scanner object to read the file
        Scanner inputFile = new Scanner(sFile);

        // Read StudentInfo
        for(int student = 1; student <= 5; student++)
        {
            String name = inputFile.nextLine();
            gradeBook.setName(student, name);
            for (int test = 0; test < 4; test++)
            {
                grades[test] = inputFile.nextDouble();
            }
        }

    // Close the file
    inputFile.close();

    }

}

And then the Gradebook class

public class Gradebook {

    // Declare fields
    private final int NUM_STUDENTS = 5;
    private final int NUM_TESTS = 4;
    // ArrayList for names of students - 5 in total
    private String[] names = new String[NUM_STUDENTS];
    // Array to store letter grades
    private char[] grades;
    // array to store each student's scores
    private double[] scores1 = new double[NUM_TESTS];
    private double[] scores2 = new double[NUM_TESTS];
    private double[] scores3 = new double[NUM_TESTS];
    private double[] scores4 = new double[NUM_TESTS];
    private double[] scores5 = new double[NUM_TESTS];


    // Method to set student's name
    public void setName(int studentNumber, String name)
    {
        names[studentNumber-1] = name;
    }

    // Method sets student scores

    public void setScores(int studentNumber, double[] scores)
    {
    switch(studentNumber)
        {
            case 1:copyArray(scores1,scores); break;
            case 2:copyArray(scores2,scores); break;
            case 3:copyArray(scores3,scores); break;
            case 4:copyArray(scores4,scores); break;
            case 5:copyArray(scores5,scores); break;
            default:break;
        }
    }

    // Returns the student's name

    public String getName(int studentNumber)
    {
    return names[studentNumber-1];
    }

    // Returns student's average score

    public double getAverage(int studentNumber)
    {
    double avg=0.0;
    switch(studentNumber)
    {
        case 1:avg = calcAverage(scores1); break;
        case 2:avg = calcAverage(scores2); break;
        case 3:avg = calcAverage(scores3); break;
        case 4:avg = calcAverage(scores4); break;
        case 5:avg = calcAverage(scores5); break;
        default:break;
    }
    return avg;
    }

    // Returns the student's letter grade

    public char getLetterGrade(int studentNumber)
    {
    char lettergrade;
    if(getAverage(studentNumber)>=90 && getAverage(studentNumber)<=100)
            lettergrade = 'A';
    else if(getAverage(studentNumber)>=80 && getAverage(studentNumber)<=89)
        lettergrade = 'B';
    else if(getAverage(studentNumber)>=70 && getAverage(studentNumber)<=79)
        lettergrade = 'C';
    else if(getAverage(studentNumber)>=60 && getAverage(studentNumber)<=69)
        lettergrade = 'D';
    else
            lettergrade = 'F';
    return lettergrade;

    }

    // Calculates the student's average

    private double calcAverage(double[] scores)
    {
    double sum=0;
    for(int i=0; i<scores.length; i++)
            sum+=scores[i];
    return sum/scores.length;

    }

    // Determines student's letter grade based on average score

    public char LetterGrade(double average)
    {
    char lettergrade;
    if(average>=90 && average<=100)
        lettergrade = 'A';
    else if(average>=80 && average<=89)
        lettergrade = 'B';
    else if(average>=70 && average<=79)
        lettergrade = 'C';
    else if(average>=60 && average<=69)
        lettergrade = 'D';
    else
            lettergrade = 'F';
    return lettergrade;
    }

    // Array copy method
    private void copyArray(double[] to, double[] from)
    {
    System.arraycopy(from, 0, to, 0, from.length);
    }


}

Here is the file the program is reading - StudentInfo.txt:

Joanne Smith
98
89
100
76
Will Jones
67
89
91
88
Kerry McDonald
78
79
88
91
Sam Young
88
98
76
56
Jill Barnes
94
93
91
98

Answer 1

You will get InputMismatchException

Reason
String name = inputFile.nextLine(); //Reads the current line, Scanner moves to next line
grades[test] = inputFile.nextDouble(); //Reads the next double value

You should be able to read first student name and grades without any issues. After reading 76, the scanner position is at the end of line 5. It didn't skip line 5.

So, when you try to read next student name by calling nextLine(). you will see "". and scanner moves to line 6.

So the next call to nextDouble() fails.

Quick fix
use Double.parseDouble(inputFile.nextLine()); for reading the double values here

Answer 2

This is a rather interesting "This can not happen" scenario. From the comments I would guess that the code actually compiled has an error in the inner for-loop. You need to find which file you are actually compiling.

Try adding random

System.out.println("Got HERE!");

to your code and see if any of them are actually printed. Because the code you show should not be able to give that exception.