public static void main(String[] args) {

    HashMap<String, Integer> books = new HashMap<>();

    books.put("book1", 1979);
    books.put("book2", 1980);
    books.put("book3", 1981);
    books.put("book4", 1982);
    books.put("book5", 1983);

    Set<String> keySet = books.keySet();
    ArrayList<String> bookList = new ArrayList<String>(keySet);
    Collection<Integer> values = books.values();
    ArrayList<Integer> listOfValues = new ArrayList<>(values);

    Collections.sort(books);

    System.out.println("The list of books is" + bookList + " Collection.sort() :\n");

    System.out.println("The list of years is" + listOfValues+ " Collection.sort() :\n");


}

I am at this point now, I'm sorry it's a lot since I'm such a noob at this. I am trying to figure out why my Collections.sort(books), books is underligned in red. I'm wondering if it has to do with the missing toString.