Java: arrays, multiple classes

Question

I have 3 classes- Car, ParkingLot and Driver. In the ParkingLot class, I have a method called parkCar which is supposed to check for the first empty spot and place the car object there:

public void parkCar(Car car) {
    for (int i = 0; i < cars.length; i++) {
        if (cars[i] == null) {
            cars[i] = car;
        }
    }
}

In the Driver class, there is supposed to be a method which calls the parkCar method to put a car object in a parking spot (driver should no longer have the car):

public void putCarInParkingSpot(Parkinglot parkingLot) {
    parkingLot.parkCar(this.car);
    this.car = null;   
}

Finally, I have a showParkingLot method in the ParkingLot class which is supposed to show all cars in the array:

public void showParkingLot() {
    for (int i = 0; i < cars.length; i++) {
        if (cars[i] != null) {
            System.out.println(cars[i].getModel());
        }
    }
}

When I use showParkingLot, the 1 car object gets placed in every spot in the array (prints it out 15 times), not just the first null spot(cars[0]). Can anyone explain why?

Community · Accepted Answer · 2017-05-23 10:33:50Z

4

Once a parking is done you need to break, see below code

public void parkCar(Car car) {
    for (int i = 0; i < cars.length; i++) {
        if (cars[i] == null) {
            cars[i] = car;
            break; // do not allocate other null spaces with same car, leave space for the next cars
        }
    }
}

Edit as suggested by Mshnik simply you can return instead of break. Post loop can be used to handle the exceptional flow, i.e. incase there is not vacant space left for parking.

public void parkCar(Car car) {
    for (int i = 0; i < cars.length; i++) {
        if (cars[i] == null) {
            cars[i] = car;
            return; // do not allocate other null spaces with same car, leave space for the next cars
        }
    }

   System.out.println("Sorry, no space left for parking");
  //here you can add code so as to see a parking space at some other place , may be you can have a 2-d array with each row representing a parking space. 
}

edited May 23, 2017 at 10:33

CommunityBot

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answered Jun 12, 2016 at 6:27

nits.kk

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3 Comments

Mshnik Over a year ago

return works as well as break here, and is a bit better style. The point of a method called parkCar is clearly to park a car, so once that is done the method should be terminated. Additionally, the post-loop area is then reserved for exception handling (i.e. there weren't any open spaces).

nits.kk Over a year ago

@anna you are most welcome, you can mark the answer as 'accepted' in case answer fully satisfies you and solves your query completely... :)

nits.kk Over a year ago

@anna also see the usage of 'return', it was suggested by Mshnik, I included it in my answer as well.

sixtytrees · Accepted Answer · 2016-07-28 21:39:44Z

0

You have two types of objects to keep track of: set of empty spots and set of cars willing to park.

parkCar deals with empty spots correctly, if (cars[i]==null)cars[i] = car;, but it doesn't check how many cars willing to park are out there. Instead you need if (cars[i]==null && setOfCarsWillingToPark.size() > 0).

Your method only parks one car, so you should use break when one spot was discovered. Since this is a method you should just use return.

answered Jul 28, 2016 at 21:39

sixtytrees

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