public void addQuestion()
    {
        boolean checkCat = false;
        Scanner scan = new Scanner(System.in);

        System.out.println("Enter the author of the question: ");

        String author = scan.nextLine();
        String category;
        while(!checkCat)
        {
            System.out.println("Enter the category of the question: ");

            category = scan.nextLine();

            for (Category c : Category.values()) {
                if (c.name().equals(category)) {
                    checkCat =  true;
                }
            }

            if(!checkCat)
            {
                System.out.println("The category must be one of these");
                for(Category c : Category.values())
                {
                    System.out.println(c);
                }
            }
        }

        System.out.println("Enter the statement of the question: ");

        String statement = scan.nextLine();

        System.out.println("Enter the answer of the question: ");

        String answer = scan.nextLine();

        Question q = new Question(author, category, statement, answer); // <---- "Change category to Category"
        addQuestion(q);
    }