@Override
	public int compareTo(Bookmark data) {
		//return (Long.parseLong(getTimestamp()) <= Long.parseLong(data.getTimestamp()) ? - 1 : 1);
		if (this.userID < data.getUserID()) {
			return -1;
		} else if (this.userID > data.userID) {
			return 1;
		} else {
			if (!this.timestamp.isEmpty() && !data.timestamp.isEmpty()) {
				if (Long.parseLong(this.timestamp) < Long.parseLong(data.timestamp)) { // < 
					return -1;
				} else if (Long.parseLong(this.timestamp) > Long.parseLong(data.timestamp)) { // >
					return 1;
				}
			}
		}
		return 0;
	}