String containing all object properties with no nulls

Question

I got these objects in constructor.

cars.add(new Car(2016, "honda", "civic"));
cars.add(new Car(2017, "Lamborghini", "aventador"));
cars.add(new Car(2000, null, "caravan"));
cars.add(new Car(2010, "dodge", null));

I need to return all the data from it in the following format: hondacivicLamborghiniaventadorcaravandodge

My function is:

public String listAllCars()
{
    String result;
    result = null;

    if(cars == null)
    {
        throw new IllegalArgumentException("c cannot be null");
    }

    for(Car car: cars)
    {

        if(car.getMake() != null || car.getModel() != null) 
        {
            result += car.getMake() + car.getModel();
        }

    }

    return result; 
}

But I end up with nullhondacivicLamborghiniaventadornullcaravandodgenull instead of hondacivicLamborghiniaventadorcaravandodge.

score 0 · Answer 1 · answered Jun 06 '20 at 04:26

0

You are checking whether any one of make or model are not null. But, your case requires you to check for both make and model individually and concatenate if present.

for(Car car: cars) {
    if(car.getMake() != null) { result += car.getMake(); }
    if(car.getModel() != null) { result += car.getModel(); }
}

answered Jun 06 '20 at 04:26

Karthik Chennupati

327
3
15

initialize result to empty string instead of null. i.e., `""` – Karthik Chennupati Jun 06 '20 at 04:36
initialized. I also need to add 2 cars data that has no null – feedthemachine Jun 06 '20 at 04:42
I don't seem to understand your requirement clearly. Can you be more clear? – Karthik Chennupati Jun 06 '20 at 04:45
If you need both make and model of the car not null, you can do `if (car.getMake() != null && car.getModel() != null)`. So, this means that you'll add the car to `result` only if it has both the make and model. If you are fine with one of the fields being null, you can use the above code. – Karthik Chennupati Jun 06 '20 at 04:51

rph · Accepted Answer · 2020-06-06T04:55:27.787

You need to append each field if it's not null independently. For compactness you may use Objects.toString. For efficiency, a simple if will do.

If you are ok with using Streams API:

public String listAllCars() {
    if (cars == null) {
        throw new IllegalArgumentException("c cannot be null");
    }

    return cars.stream()
            .map(c -> Objects.toString(c.getMake(), "")
                    + Objects.toString(c.getModel(), ""))
            .reduce("", (a, b) -> a + b);
}

Or, using the imperative style, but with a StringBuilder:

public String listAllCars() {
    if (cars == null) {
        throw new IllegalArgumentException("c cannot be null");
    }

    StringBuilder result = new StringBuilder();

    for (Car car : cars) {
        result.append(Objects.toString(car.getMake(), ""));
        result.append(Objects.toString(car.getModel(), ""));
    }

    return result.toString();
}

Or, without the StringBuilder:

public String listAllCars() {
    if (cars == null) {
        throw new IllegalArgumentException("c cannot be null");
    }

    String result = "";

    for (Car car : cars) {
        result += Objects.toString(car.getMake(), "");
        result += Objects.toString(car.getModel(), "");
    }

    return result;
}

Yes, added to the answer, but bear in mind that StringBuilder is the recommended way of appending strings in Java. — rph, Jun 06 '20 at 04:51

String containing all object properties with no nulls

2 Answers2