程序编译但在给定文件名时不会运行

Question

Working on this program that takes scores form a file and calculates averages, and then tells the averages from the user. Everything is done though I'm not sure why it wont accept my file scores.txt

scores.txt (the file that contains the students scores)

5
6
95.2 89.1 98.0 78.9 100 67
100 99.6 100 100 90.1 82.2
100 85.5 85.1 74 81 79.4
98.6 71.5 68.9 62.4 56.9 0
100 100 100 88.3 91.6 81.3

StudentGradebookScores.java

import java.io.*;
import java.text.DecimalFormat;
import java.util.*;

public class StudentGradebookScores {
    public static void main(String[] args) throws IOException {
        DecimalFormat FMT = new DecimalFormat("#.#");

        try (Scanner input = args.length > 0 ? new Scanner(new File(args[0]))
                : new Scanner(System.in)) {
            GradeBook book = new GradeBook(input);
            System.out.println(book);
            System.out.printf("Overall Average: %s\n",
                    FMT.format(book.average()));
        }
    }
}

GradeBook.java

import java.io.*; 
import java.text.*;
import java.util.*;
import java.util.stream.*;

public class GradeBook {
    private List<double[]> students;
    private static final DecimalFormat FMT = new DecimalFormat("#.#");

    public GradeBook(Scanner input) {
        this.students = new ArrayList<double[]>();
        while (input.hasNextLine()) {
            double[] student = Arrays.stream(input.nextLine().trim().split("\\s+"))
                  .mapToDouble(Double::parseDouble)
                  .toArray();
            students.add(student);
        }
    }

    public double getScore(int student, int assignment) {
        return this.students.get(student)[assignment];
    }

    public double averageForStudent(int student) {
        return Arrays.stream(this.students.get(student))
                     .average()
                     .getAsDouble();
    }

    public double averageForAssignment(int assignment) {
        return this.students.stream()
                   .mapToDouble((assignments) -> assignments[assignment])
                   .average()
                   .getAsDouble();
    }

    public double average() {
        return IntStream.range(0, this.students.size())
                        .mapToDouble((s) -> this.averageForStudent(s))
                        .average()
                        .getAsDouble();
    }

    public String toString() {
        StringBuilder out = new StringBuilder();
        int numAssignments = this.students.stream()
                                 .mapToInt((assignments) -> assignments.length)
                                 .max()
                                 .getAsInt();

        // Header
        out.append("\t\t\t\tAssignment #:\n\t\t");
        for (int a = 0; a < numAssignments; a++) {
           out.append(a + 1).append('\t'); 
        }
        out.append("Avg\n");

        // Body
        for (int s = 0; s < this.students.size(); s++) {
            out.append("Student #").append(s + 1).append(":\t");
            for (int a = 0; a < numAssignments; a++) {
                out.append(FMT.format(this.getScore(s, a))).append('\t');
            }
            out.append(FMT.format(this.averageForStudent(s))).append('\n');
        }

        // Footer
        out.append("Average\t\t");
        for (int a = 0; a < numAssignments; a++) {
            out.append(FMT.format(this.averageForAssignment(a))).append('\t');
        }
        out.append('\n');

        return out.toString();
    }

    public static void main(String[] args) throws IOException {
        try (Scanner input = args.length > 0 ? new Scanner(new File(args[0])) :
                                               new Scanner(System.in)) {
            GradeBook book = new GradeBook(input);
            System.out.println(book);
            System.out.printf("Overall Average: %s\n",
                              FMT.format(book.average()));
        }
    }
}

I click compile, nothing. Type scores. Get a huge error. Recompile. Try scores.txt, still getting a huge error.

EDIT: I get this type of error

Exception in thread "main" java.lang.NumberFormatException: For input string: "scores"
    at sun.misc.FloatingDecimal.readJavaFormatString(Unknown Source)
    at sun.misc.FloatingDecimal.parseDouble(Unknown Source)
    at java.lang.Double.parseDouble(Unknown Source)
    at GradeBook$$Lambda$1/523429237.applyAsDouble(Unknown Source)
    at java.util.stream.ReferencePipeline$6$1.accept(Unknown Source)
    at java.util.Spliterators$ArraySpliterator.forEachRemaining(Unknown Source)
    at java.util.stream.AbstractPipeline.copyInto(Unknown Source)
    at java.util.stream.AbstractPipeline.wrapAndCopyInto(Unknown Source)
    at java.util.stream.AbstractPipeline.evaluate(Unknown Source)
    at java.util.stream.AbstractPipeline.evaluateToArrayNode(Unknown Source)
    at java.util.stream.DoublePipeline.toArray(Unknown Source)
    at GradeBook.<init>(GradeBook.java:21)
    at StudentGradebookScores.main(StudentGradebookScores.java:16)

Answer 1

I click the tab in Eclipse that shows my StudentGradebookScores.java. I click the green play button that stands, I click in the Console and type scores or scores.txt

And your program as written will then promptly try to parse scores or scores.txt as a number. Either load your command line parameters (Eclipse will let you do this you know), or allow your program to accept a file name and use this to open a file from Scanner input -- your program does not do this at present.

In other words, change this:

   try (Scanner input = args.length > 0 ? new Scanner(new File(args[0]))
            : new Scanner(System.in)) {
        GradeBook book = new GradeBook(input);
        System.out.println(book);
        System.out.printf("Overall Average: %s\n",
                FMT.format(book.average()));
    }

to something like

   if (args.length == 0) { 
       Scanner tempScanner = new Scanner(System.in);
       System.out.print("Enter file name: ");
       String fileName = tempScanner.nextLine();
       File file = new File(fileName);
       tempScanner.close();
       Scanner input = new Scanner(file);

       //.....
   }