class Book
{
    // The fields.
    private String author;
    private String title;
    private int pages;
    private String refNumber;

    /**
     * Set the author and title fields when this object
     * is constructed.
     */
    public Book(String bookAuthor, String bookTitle, int amountPages, String setRef)
    {

        if(setRef == null)
        {
            refNumber = "";
            author = bookAuthor;
            title = bookTitle;
            pages = amountPages;
        }
        if(setRef!= null)
        {
            refNumber = setRef;
            author = bookAuthor;
            title = bookTitle;
            pages = amountPages;
        }
    }

    public String returnAuthor()
    {
        return author;
    }

    public int getPages()
    {
        return pages;
    }

    public String returnTitle()
    {
        return title;
    }

    public void printAuthor()
    {
        System.out.println(author);
    }

    public void printTitle()
    {
        System.out.println(title);
    }

    public void printDetails()
    {
        System.out.println("Titel : " + title);
        System.out.println("Auteur : " + author);
        System.out.println("Aantal pagina's : " + pages);