Library.java

class Library…
  public Book[] booksAuthoredBy(String arg) {
      List allBooks = finder.findAll();
      for (Iterator it = allBooks.iterator(); it.hasNext();) {
          Book book = (Book) it.next();
          if (!book.getAuthor().equals(arg)) it.remove();
      }
      return (Book[]) allBooks.toArray(new Book[allBooks.size()]);
  }