Homework - How to handle FileNotFoundException's?

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

class assignment3 {

    assignment3(int n, int g) throws IOException {

        // int n is our input_number, int g is our no_of_interations
        
        final String brk = "----------------------";

        // Listing variables used for requirements:        
        double a;
        double b;
        double c; // variable to store double entered from KBD

        // Requirement #3 addressed

        if(n == 0){
            System.out.println("Please rerun the program entering a non-zero in the command line.");
            System.exit(0);  // Quits the application
        }

        // Requirement #7 addressed

        int count = 1;
        while (count <= g) {

            // Requirement #4 addressed

            Scanner in = new Scanner(System.in);
            System.out.print("Please enter a coefficient: ");
            a = Double.parseDouble(in.nextLine());
            System.out.print("Please enter a coefficient: ");
            b = Double.parseDouble(in.nextLine());
            System.out.print("Please enter a coefficient: ");
            c = Double.parseDouble(in.nextLine());

            // Requirement #1 addressed

            if(n > 0){
                double root1 = (-b + Math.sqrt(b*b-4*a*c))/(2*a);
                double root2 = (-b - Math.sqrt(b*b-4*a*c))/(2*a);

                // Requirement #5 addressed

                PrintWriter out = new PrintWriter(new FileWriter("results.dat", true));
                out.println("Quadratic equation with the following coefficients:");
                out.println("a: " + a + ";" + " b: " + b + ";" + " c: " + c + ";");
                out.println("has the following roots: " + root1 + " and " + root2);
                out.println(brk);
                out.close();  // Closing a file after writing to it.

                boolean b1 = Double.isNaN(root1);
                boolean b2 = Double.isNaN(root2);

                if(b1 || b2) {
                    System.out.println(" ");
                    System.out.println("Quadratic equation with the following coefficients:");
                    System.out.println("a: " + a + ";" + " b: " + b + ";" + " c: " + c + ";");
                    System.out.println("does not have roots in the real domain.");
                }
            }

            // Requirement #2 addressed

            if (n < 0){
                double y=0; //For finding ymin
                double x=0; //For finding ymin

                //Use quadratic functions derivative to find xmin, a*x+b=0
                x = -b/(2*a);
                //Use xmin in original quadratic equation to find ymin value:
                y = (a*(x*x)+b*x+c);

                // Requirement #6 addressed

                PrintWriter out = new PrintWriter(new FileWriter("results.dat", true));
                out.println("Quadratic equation with the following coefficients:");
                out.println("a: " + a + ";" + " b: " + b + ";" + " c: " + c + ";");
                out.println("has the following minimum: " + y + " at point " + x);
                out.println(brk);
                out.close();  // Closing a file after writing to it.

                boolean y1 = Double.isNaN(y);

                if(y1) {
                    System.out.println(" ");
                    System.out.println("Quadratic equation with the following coefficients:");
                    System.out.println("a: " + a + ";" + " b: " + b + ";" + " c: " + c + ";");
                    System.out.println("does not have a minimum.");
                }
            }
            count++;
        }
    }

   public static void main(String args[]) throws IOException {

        // Requirement #0 addressed

        try {
            new assignment3(Integer.parseInt(args[0]), Integer.parseInt(args[1]));
        }
        catch (ArrayIndexOutOfBoundsException e) {
            System.out.println("No parameters in the command line entered; default values of 1 assumed.");
            new assignment3(1, 1);
        }
        catch (NumberFormatException e) {
            System.out.println("Please only enter integers into the command line next time.");
            System.out.println("System Exiting.");
            System.exit(0);
        }
        catch (FileNotFoundException e){
            System.out.println("The file \"results.dat\" doesn't exist, or is read-only.");
            System.out.println("System Exiting.");
            System.exit(0);
        }
   }
}