public Ticket in(Car car) {
		if(isFull()) {
			throw new ParkException("停车场已满，不能停车了。");
		}
		int num = this.parkBoyList.size();
		if(this.park != null) {
			num += 1;
		}
		Random random = new Random();
		while(true) {
			int i = random.nextInt(num);
			if(i == 0 && !this.park.isFull()) {
				return park.in(car);
			} else if(i > 0) {
				ParkBoy boy = this.parkBoyList.get(i - 1);
				if(!boy.isFull()) {
					return boy.in(car);
				} else {
					continue;
				}
			} else {
				continue;
			}
		}
	}