/* 9/25/2019
 * 
 * introduce input files
 *     Must put the following 2 things:
 *     (a) import the java.io pkg
 *     (b) put "throws IOException"
 *     for input files, use 2 classes
 *     File and Scanner
 */
import java.util.Scanner;
import java.io.*;

/** In version 2 of ReadGrades, we use a variable for filename, show how to do in 1 stmt,
  * show how to check if file exists
  */
public class ReadGradesV2 {
  /** main reads in a number of grades from an input file
    * NOTE: we have 2 Scanner objects, one is connected to an input file, and the other
    * to the keyboard
    */
  public static void main(String[] args) throws IOException { 
    // create a Scanner object and connect to keyboard
    Scanner keyboard = new Scanner(System.in);
    System.out.println("Enter file name for input file: ");
    String filename = keyboard.next();
    // create a File object
    File infile = new File(filename);
    // create a Scanner object and connect it to the File object
    // Scanner dataFile = new Scanner(new File(filename));
    if (!infile.exists()) { // exists is a  method in the File class and it checks whether a 
                            // file can be found.
        System.out.println("No file with the name " + filename + " can be found.");
        System.exit(1); // terminate the program exit FAILURE
    }
    
    Scanner dataFile = new Scanner(infile);
    // now we can use all the methods of the Scanner class
    int grade;
    while (dataFile.hasNextInt()) {  // reads until EOF only if there are integers
        grade = dataFile.nextInt();
        System.out.println("grade read in: " + grade);
    }
    // close both Scanner objects
    keyboard.close();
    dataFile.close();
  }
}