How do I get the list of numbers off of a file that the user inputs in Java?

Question

I am using Java eclipse and I would like to have the user input the filename to retrieve a list of scores from the file. My goal is to take the average of those numbers. What line of code do I need just to get the user to input a file name and for the program to take those numbers so that I can compute with them? Currently I can have the user input scores, But I need to get the numbers from the file instead. I have visited numerous resources on this site. Here are a few:

BufferedReader, Error finding file, Getting a list from a file

package Average;
/**An average of scores*/
import java.util.Scanner;

public class Average2 {

    public static void main(String[] args) {
        int grade = 0;
        int students = 0;
        float total = 0;
        double average = 0;

        Scanner input = new Scanner(System.in);

        System.out.println("Enter number of students: ");
        students = input.nextInt();

        if (students <= 10) {
            System.out.println("Enter the grades of the students: ");

            for(int i = 0; i < students; i++) {
                do {
                    grade = input.nextInt();

                } while(grade < 0 || grade > 100);

                total += grade;
            }

            average = (total/students);
            int median = ((82+84)/2);

            System.out.println("The average is " + average);
            System.out.println("The mean is " + median);


        }
    }
}

Update since above post!

package trials;

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

public class trials2 {

public static void main(String[] args) throws IOException {
    // TODO Auto-generated method stub
    // Create new Scanner object to read from the keyboard
    Scanner in = new Scanner(System.in);

    // Grab the name of the file
    System.out.println("Enter filename: ");
    String fileName = in.next();

    // Access the file
    Scanner fileToRead = new Scanner(new File(fileName));

    // While there is still stuff in the file...
    double sum = 0;
    while (fileToRead.hasNext()) { 
                if (fileToRead.hasNextDouble()) {
                    sum += fileToRead.nextDouble();
                } else {
                    fileToRead.next();
                }   
            }
   {
            fileToRead.close();
        }

        System.out.println(sum);
}
}

The results I get from this:

Enter filename:

esp.txt <--entered by me

501.0

Answer 1

Scanner userInput = new Scanner(System.in);
System.out.println("ENter filename");
String fileName = userInput.next();
Scanner fileScan = new Scanner(new File(fileName));

then use scanner methods to process lines or string tokens you are interested in.

Answer 2

Look at the Java tutorial on Scanning: http://docs.oracle.com/javase/tutorial/essential/io/scanning.html, particularly the ScanSum example. It shows how to scan double values from a text file and add them. You should be able to modify this example for your project.

Answer 3

Given that you want to find the average of numbers in a file, you could do something like this:

// Create new Scanner object to read from the keyboard
Scanner in = new Scanner(System.in);

// Grab the name of the file
System.out.println("Enter filename: ");
String fileName = in.next();

// Access the file
Scanner fileToRead = new Scanner(new File(fileName));

// Initialize our relevant counters
double sum = 0.0;
int numStudents = 0;

// While there is still stuff in the file...
while (fileToRead.hasNext()) { 
    // Is this next line consisting of just a number?
    if (fileToRead.hasNextDouble()) {
        // If it is, accumulate
        sum += fileToRead.nextDouble();
        numStudents++;
     } 
     else { // Else, just skip to the next line
         fileToRead.next();
     }   
}  
// Close the file when finished
fileToRead.close();

// Print the average:
System.out.println("The average mark is: " + (sum / numStudents));

This code will create a new Scanner object that will read input from your keyboard. Once it does that, you type in the file name, and it gets access to this file by opening another Scanner object. After that, we initialize some counters to help us calculate the average. These are sum, which will add up all of the marks we encounter and numStudents, which keeps track of how many students there are in the file.

The while loop will keep looping through each line of this file until it reaches the end. What is important is that you check to see whether or not the line you are reading in next consists of a single number (double). If it is, then add this to our sum. If it isn't, skip to the next line.

Once you're finished, close the file, then display the average by taking the sum and dividing by the total number of students we have encountered when reading the numbers in the file.

Just took a look at your profile and your profile message. You have a long road ahead of you. Good luck!