Sorting alphabetically in 2 different ways using classes

I have a program where I have take an array of books and give the user the choice to sort alphabetically by author or title. I have a Book class with Author and Title variables, as well as setters and getters.

I have tried looking at other threads with very similar questions, but the fix still gives me errors. The one I recently tried was using Collections.sort(books, Comparator.comparing(Book:getTitle)). This gave me an error for conflicting arguments. I have also tried adding a custom compareTo method to my Book class, but I can't seem to find a way to use that for both Author and Title.

What is the best way to go about this?

You can also use the Comparator Interface in the book object itself. This could look like follows. It sorts per author first, then per title. From the JavaDocs the compareTo int result needs to follow the spec:
Returns:
a negative integer, zero, or a positive integer as this object is less than, equal to, or greater than the specified object.

public class Book implements Comparable{
    private String author;
    private String title;

    public Book(String author, String title){
        this.author = author;
        this.title = title;
    }

    public String getAuthor() {
        return author;
    }

    public String getTitle() {
        return title;
    }


    @Override
    public int compareTo(Object o) {
        Book other = (Book) o;

        //Your compare code goes here
        int result = this.author.compareTo(other.author);
        if(result ==0){
            result = this.title.compareTo(other.title);
        }
        return ;
    }
}

When you want to use different sorting you can use the Comparator object:

public class AuthorComparator implements Comparator<Book>{

    @Override
    public int compare(Book a, Book b) {
        return a.getAuthor().compareTo(b.getAuthor());
    }
}

public class TitleComparator implements Comparator<Book>{

    @Override
    public int compare(Book a, Book b) {
        return a.getTitle().compareTo(b.getTitle());
    }
}

Sorting Arrays of books using Comparator classes:

book[] books = getBooksFromSomewhere();
Arrays.sort(books, new TitleComparator());

//now resort by Author
Arrays.sort(books, new AuthorComparator());

If you have a list of Book Object named 'books' there's easier and more flexible ways into achieving what you want using streams:

private void printBooksByTitle(List<Book> unsortedBooks)
        List<Book> titleSortedBooks = unsortedBooks.stream()
			.sorted(Comparator.comparing(Book::getTitle))
			.collect(Collectors.toList());

        titleSortedBooks.forEach(System.out::println);
}

Version for Array of Books (for the updated question):

private Book[] sortBooksByTitle(Book[] books){
    Book[] titleSortedBooks = Arrays.stream(books)
			.sorted(Comparator.comparing(Book::getTitle))
			.collect(Collectors.toArray(Book[]::new););
}