public boolean start() {
		boolean startflag = false;
		if (gas.empty() && battery.empty()) {
			System.out.println("Gas and Battery are empty.");
		} else if (gas.empty() && !battery.empty()) {
			System.out.println("Gas is empty.");
		} else if (!gas.empty() && battery.empty()) {
			System.out.println("Battery is empty");
		} else {
			startflag = true;
			System.out.println("You can Start!");
		}
		return startflag;
	}