使用扫描仪读取文本文件时出现问题

Question

I'm trying to read data from a text file, but I'm having trouble getting it to work. This is what I have so far

import java.io.File;
import java.io.FileNotFoundException;
import java.util.*;

    public class Student {
        private String firstName;
        private String lastName;
        private int homeworkScore;
        private int testScore;
        private String letterGrade;
        private int numberOfStudents;

        public Student() {

            numberOfStudents = 0;
            homeworkScore = 0;
            testScore = 0;

        }

        public static void main(String[] args) {

            Scanner scanner = null;
            try {
                scanner = new Scanner(new File("grades.txt"));
            } catch (FileNotFoundException e) {
                System.out
                        .println("Error opening file. Please make sure that you have a grades.txt file in the same folder as GradeCalculator.class");
                System.exit(0);
            }
        }

        public void setNumberOfStudents() {
            Scanner scanner = new Scanner(System.in);
            numberOfStudents = scanner.nextInt();

        }

        public void setFirstName() {
            Scanner scanner = new Scanner(System.in);
            String firstName = scanner.next();
        }

        public void setLastName() {
            Scanner scanner = new Scanner(System.in);
            String lastName = scanner.next();
        }
    }

And this is the driver class I have so far:

public class CourseGrade {

    public static void main(String[] args) {
        Student myStudent = new Student();
        myStudent.setNumberOfStudents();
        myStudent.setFirstName();
        myStudent.setLastName();
    }

}

When I run the driver class, nothing happens, so I'm not sure if it's actually setting the values to what I want. I know the file is being read because I'm not getting the error message, but I'm not sure if the values are actually being set

Answer 1

You aren't actually iterating through the file with your scanner. All you're doing is initializing the Scanner object with the file.

You'll need to do something like:

 while (scanner.hasNextLine()) {
    String line = scanner.nextLine();
    //do stuff...
 }

As was pointed out in the comment section of your question, the Scanner is being initialized in your Student class main method - which seems wrong. You could have a static method on Student that reads this file and constructs the Student object based on the data.

Answer 2

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

public class Student {
    private String firstName;
    private String lastName;
    private int homeworkScore;
    private int testScore;
    private String letterGrade;
    private int numberOfStudents;

    public Student() {

        Scanner scanner = null;
        try {
            scanner = new Scanner(new File("grades.txt"));
        } catch (FileNotFoundException e) {
            System.out
                    .println("Error opening file. Please make sure that you have a grades.txt file in the same folder as GradeCalculator.class");
            System.exit(0);
        }

        //Assumed file content is as expected
        this.numberOfStudents = scanner.nextInt();
        this.firstName = scanner.next();
        this.lastName = scanner.next();
    }
}

And following driver class will print the values set when calling constructor.

public class CourseGrade {

  public static void main(String[] args) {

    Student myStudent = new Student();
    //Your requirement is done by now
  }

}

Answer 3

Ok, I got it to work, and this is what I did:

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

public class Student {
    private String firstName;
    private String lastName;
    private int homeworkScore;
    private int testScore;
    private String letterGrade;
    private int numberOfStudents;
    Scanner scanner = null;
    {
        try {
            scanner = new Scanner(new File("grades.txt"));
        } catch (FileNotFoundException e) {
            System.out
                    .println("Error opening file. Please make sure that you have a grades.txt file in the same folder as GradeCalculator.class");
            System.exit(0); // Error message is shown when file is not found
        }
    }

    public Student() {
        homeworkScore = 0;
        testScore = 0;
        numberOfStudents = 0;

    }

    public void setNumberOfStudents() {
        numberOfStudents = scanner.nextInt();

    }

    public int getNumberOfStudents() {
        return numberOfStudents;
    }

    public void setFirstName() {
        firstName = scanner.next();

    }

    public String getFirstName() {
        return firstName;
    }

    public void setLastName() {

        lastName = scanner.next();
    }

    public String getLastName() {
        return lastName;
    }

    public void setHomeworkScore() {

    }

    public int getHomeworkScore() {
        return homeworkScore;
    }

    public void setTestScore() {

    }

    public int getTestScore() {
        return testScore;
    }
}

And then when I run this new driver class:

public class CourseGrade {

    public static void main(String[] args) {
        Student myStudent = new Student();
        myStudent.setNumberOfStudents();
        myStudent.setFirstName();
        System.out.print(myStudent.getFirstName() + " ");
        myStudent.setLastName();
        System.out.print(myStudent.getLastName());

    }

}

It prints out the name of the first person in the text file! I still have to set up the methods for computing test and homework score, but it seems to all be working now. Thanks for the help!