public Book longestTitleForEach(Book book) {
		if (nbBook == 0) {  //Si nombre de book = 0 alors il n'y a pas de book
			return null;
		}
		Book longuestTitle = books.get(0);  //on stock le livre qui a pour l'instant la plus grande taille
		int longuestSize = longuestTitle.getTitle().length();

		    books.forEach((i) -> {

			Book currentBook = i;
			int currentSize = currentBook.getTitle().length();
			if (currentSize > longuestSize) {
			    longuestTitle = currentBook;
				longuestSize = currentSize;
			}
		    });
		return longuestTitle;
	}