ClassAverages.java

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

public class ClassAverages {
    public static void main(String[] args) throws FileNotFoundException {

        Scanner scan = new Scanner(System.in);
        System.out.print("\nEnter the filename: ");
        String filename = scan.nextLine();
        filename += ".txt";

        System.out.println("\nCalling \"inputScores()\" method...");
        inputScores(filename);

        System.out.println("\nCalling \"outputScores()\" method...");
        outputScores(filename);

    } // end main()

    private static void inputScores(String someFileName) throws FileNotFoundException {

        Scanner scan = new Scanner(System.in);
        int studentNumber = 1;

            try {
                PrintWriter outputFile = new PrintWriter(someFileName); // create an instance of the
                // PrintWriter class to write data to file

                System.out.printf("\nEnter score for user %,d: (enter -1 to exit): ", studentNumber);
                double score = scan.nextDouble();
                System.out.println(); // spacing for readability
                while (score < -1.0) {
                    System.out.printf("A score of %,.2f is invalid.", score);
                    System.out.printf("\nEnter score for user %,d: (enter -1 to exit): ", studentNumber);
                    score = scan.nextInt();
                    System.out.println(); // spacing for readability
                }

                while (score != -1) {
                    outputFile.println(score); // println method writes a line of data to a file.
                    studentNumber++; // increment Student #
                    System.out.printf("Enter score for user %,d: (enter -1 to exit): ", studentNumber);
                    score = scan.nextDouble();
                    System.out.println(); // spacing for readability

                    while (score < -1.0) {
                        System.out.printf("A score of %,.2f is invalid.", score);
                        System.out.printf("\nEnter score for user %,d: (enter -1 to exit): ", studentNumber);
                        score = scan.nextDouble();
                    }
                }
                System.out.println("All values entered have been written to the file " +
                        "\"" + someFileName + "\"");
                outputFile.close();
                scan.close();
            } catch (InputMismatchException e) {
                System.out.println("\nInvalid input detected. \nEnding program now.\nGoodbye!");
                //System.out.println("ERROR: " + e.toString());
                System.exit(0);
        }

    } // end inputScores()

    private static void outputScores(String someFileName) throws FileNotFoundException {
        System.out.println("____________________________________________________________");
        System.out.printf("\n\nOPENING FILE \"%s\"\n", someFileName);
        // creates an instance of the File class
        // Pass String parameter to the File object constructor
        File fileToRead = new File(someFileName);
        if (!fileToRead.exists()) { // Not necessary but for safe-handling, just in case
            System.out.println("\nFile does not exist.");
            System.exit(0);
        }

        // Pass a reference to this File object as an argument to the Scanner class constructor
        // This creates a Scanner object that uses the file someFileName as its source of input.
        Scanner fileToReadScanner = new Scanner(fileToRead);
        int index = 1;
        double sumOfScores = 0;
        double scoreInFile;
        double countOfScores = 0;

        // Read lines from the file until no more are left.
        while (fileToReadScanner.hasNext()) {
            // Read the next line
            String value = fileToReadScanner.nextLine();

            // Display the last line read
            System.out.printf("\n\tStudent %,d  :  %s\n", index, value);
            index++; // increment Student # for printing purposes
            scoreInFile = Double.parseDouble(value); // parse integer values in lines for average
            // calculation
            countOfScores++; // increment number of scores for average calculation
            sumOfScores += scoreInFile; // get sum of all scores
        }


        System.out.printf("\n\tClass Test Score Average  :  %,.2f",
                (sumOfScores/countOfScores));
        System.out.print("\n\nEND FILE.\n\n");
        System.out.println("____________________________________________________________");
        fileToReadScanner.close();
    }
}