adding and retrieving objects from a list

Question

My goal is to have a list of cars as an Object so that, I can retrieve a Car from that list. As well as get details of the cars. Can someone point me to the right direction

What I have done so far.

Create a class called Car and have the variables CarNum, carName, carPlate;
generated getters and setters for the variables and a toString as the carName
Create a class called CarCollection as follows

.

 public class CarCollection {
        private List<CarItem> mCarList;



        public void addVan(CarItem v) {
            mCarList.add(v);
        }

        public List<CarItem> getCarList() {
            return mCarList;
        }

The following test doesn't work. Why?

public class TestCarCollectionprocess {

    public static void main(String[] args) {

        CarItem car1 = new CarItem();
        car1.setmCarName("Pedro");
        car1.setmCarNum(1);

        CarItem car2 = new CarItem();
        car2.setmCarName("Rene");
        car2.setmCarNum(2);

        CarCollection carList = new CarCollection();        
        carList.addCar(car1);
        carList.addCar(car2);
        System.out.println(carList.getCarList());
    } 
}

I don't see an addCar method in your CarCollection class and I don't see if you are fully constructing the private List mCarList; — Michael Markidis, Apr 28 '16 at 18:53
Your should READ the exception you get. It tells exactly what and where the problem is. http://stackoverflow.com/questions/218384/what-is-a-null-pointer-exception-and-how-do-i-fix-it — JB Nizet, Apr 28 '16 at 19:04

score 3 · Accepted Answer · answered Apr 28 '16 at 18:55

3

What I see from your code, you should get NullPointerException in addVan method since you didn't initialize List, so change it like this:

 private List<CarItem> mCarList = new ArrayList<>();

answered Apr 28 '16 at 18:55

Adnan Isajbegovic

2,227
17
27

1

Thanks. This was the answer I was looking for! – Apr 28 '16 at 19:01

score 0 · Answer 2 · answered Apr 28 '16 at 18:54

0

You are trying to add a CarItem to the CarCollection's mCarList without ever instantiating the list so you should be getting a null reference exception. In your carCollection class, create a constructor that sets

mCarList = new List<CarItem>();

answered Apr 28 '16 at 18:54

Trevor Ward

602
3
12

no, IList is an interface, List is an implementation of the interface – Trevor Ward Apr 28 '16 at 18:57

adding and retrieving objects from a list

2 Answers2