Creating Objects dynamically at runtime with possible member values

Question

I have a class of which objects I want to get instantiated at runtime and stored in a collection of such objects. However, the number of such objects can be dynamic in nature.

Let say,

class Car{
    private Color color;
    private Brand brand;
    //AllArgsConstructor
}

enum Color{
   RED, BLUE
}

enum Brand{
   VW, SUZUKI, HONDA
}

Now I want objects with all UNIQUE possible permutations from 2 enums(in this case 2*3 = 6) to be created at runtime and added to a collection.

If I were to do this manually, I would do:

Car carRV = new Car(Color.RED, Brand.VW);
Car carRS = new Car(Color.RED, Brand.SUZUKI);
Car carRH = new Car(Color.RED, Brand.HONDA);
Car carBV = new Car(Color.BLUE, Brand.VW);
Car carBS = new Car(Color.BLUE, Brand.SUZUKI);
Car carBH = new Car(Color.BLUE, Brand.HONDA);

//addToCollection

But the problem with the above is too much coding and very manual to keep on adding as a new enum value is added. Is there a better way to do this?

Thanks in advance :)

Master Chief · Accepted Answer · 2021-04-14 09:08:31Z

1

Yop can use a nested for loop to create car objects

private Car createCar() {
    List<Car> cars = new ArrayList<>();
    for(Color color : Color.values()) {
        for(Brand brand : Brand.values()) {
            cars.add(new Car(color, brand));
        }
    }
    return cars;
}

answered Apr 14, 2021 at 9:08

Master Chief

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Comments

Giorgi Tsiklauri · Accepted Answer · 2021-04-14 09:24:49Z

I personally think, that generating objects this way, is not the best thing to do, as it does not exhibit dynamic nature: your code will be dependent on a few other factors and breaking those factors will break your code.

However, if you're sure, that this is what you want, you might consider something like:

List<Car> cars = new ArrayList<>();

for (int i = 0; i < Color.values().length; i++) {
    for (int j = 0; j < Brand.values().length; j++) {
        cars.add(new Car(Color.values()[i], Brand.values()[j]));
    }
}

//or, even simpler

for (Color color : Color.values()) {
    for (Brand brand : Brand.values()) {
        cars.add(new Car(color, brand));
    }
}

and then,

for (Car car : cars) {
    System.out.println(car);
}

would print:

Car{color=RED, brand=HONDA}
Car{color=RED, brand=SUZUKI}
Car{color=RED, brand=VW}
Car{color=BLUE, brand=HONDA}
Car{color=BLUE, brand=SUZUKI}
Car{color=BLUE, brand=VW}

assuming that .toString() method is overriden.

The-Proton-Resurgence · Accepted Answer · 2021-04-14 09:23:55Z

0

I am finally doing it like this:

EnumSet.allOf(Color.class).forEach(color -> EnumSet.allOf(Brand.class).forEach(brand -> carList.add(new Car(color, brand))));

answered Apr 14, 2021 at 9:23

The-Proton-Resurgence

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2 Comments

Giorgi Tsiklauri Over a year ago

Prefer using normal for-loop in this case. Readability is dead in this code.. streams are not always better than ordinary loops. :)

user4910279 Over a year ago

He doesn't use stream.

DigitShifter · Accepted Answer · 2021-04-14 10:26:10Z

Alternative design:

Demo class:

public class Demo {

    public static void main(String[] args) {
        List<Car> allCarCombinations = CarProducer.newInstance().getAllCarCombinations();
        System.out.println("All car combinations: ");
        allCarCombinations.forEach(System.out::println);
        System.out.println("Total number of cars: " + allCarCombinations.size());
    }

}

Car class:

public class Car {

    private final Color color;
    private final Brand brand;

    public Car(Color color, Brand brand) {
        this.color = color;
        this.brand = brand;
    }

    public Color getColor() {
        return color;
    }

    public Brand getBrand() {
        return brand;
    }

    @Override
    public String toString() {
        return "Car{" +
                "color='" + color + '\'' +
                ", brand='" + brand + '\'' +
                '}';
    }
}

Color enum:

public enum Color {
    RED, BLUE;
}

Brand enum:

public enum Brand {
    VW, SUZUKI, HONDA;
}

CarProducer class:

public final class CarProducer {

    private List<Car> allCarCombinations;

    private CarProducer() {
        allCarCombinations = new ArrayList<>();
    }

    public static CarProducer newInstance() {
        return new CarProducer();
    }

    public List<Car> getAllCarCombinations() {
        if(allCarCombinations.isEmpty()) {
            addAllCars();
        }
       return allCarCombinations;
    }

    private void addAllCars() {
        for (Brand brand : Brand.values()) {
            for (Color color : Color.values()) {
                allCarCombinations.add(new Car(color, brand));
            }
        }
    }

}

Output:

All car combinations: 
Car{color='RED', brand='VW'}
Car{color='BLUE', brand='VW'}
Car{color='RED', brand='SUZUKI'}
Car{color='BLUE', brand='SUZUKI'}
Car{color='RED', brand='HONDA'}
Car{color='BLUE', brand='HONDA'}
Total number of cars: 6

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