@Override
	public int hashCode() {
		final int prime = 31;
		int result = 1;
		result = prime * result + ((author == null) ? 0 : author.hashCode());
		result = prime * result + ((genre == null) ? 0 : genre.hashCode());
		long temp;
		temp = Double.doubleToLongBits(price);
		result = prime * result + (int) (temp ^ (temp >>> 32));
		result = prime * result + quantity;
		result = prime * result + ((title == null) ? 0 : title.hashCode());
		return result;
	}