refactoring: adding String for 'courseData.txt' file

src/main/java/org/example/Main.java

@@ -2,6 +2,8 @@ package org.example;
 import java.util.Scanner;
 
 public class Main {
+
+    public static final String courseData_file = "courseData.txt";
     public static void main(String[] args) {System.out.println("Hello world!");
 
         Administration administration = new Administration();
@@ -31,11 +33,11 @@ public class Main {
                     break;
                 case 3:
                     System.out.println("Add Course selected");
-                    Course.addCourseFromUserInput("courseData.txt");
+                    Course.addCourseFromUserInput(courseData_file);
                     break;
                 case 4:
                     System.out.println("Delete Course selected");
-                    Course.deleteCourse("courseData.txt");
+                    Course.deleteCourse(courseData_file);
                     break;
                 case 5:
                     System.out.println("Assign Grade selected");