Create objects from a list of IDs in a simple way

Question

Is there a way to simplify the following with a stream or something?

final List<Fruit> fruits = new ArrayList<>(fruitIds.size());
for (final long id : fruitIds) {
   final var fruit = new Fruit();
   fruit.setId(id);

   fruits.add(fruit);
}

Thank you very much in advance

Answer 1

Using a constructor would be optimal. This assumes an int id.

class Fruit {
    int id;
   
    public Fruit(int id) {
        this.id = id;
    }
    public void setId(int id) {
        this.id = id;
    }
}

for (Fruit id : fruitIds) {
    Fruits.add(new Fruit(id));
}

But if you aren't allowed to modify your Fruit class creating another class to act as a Factory class would work. Again I am presuming id is an int.

List<Fruit> fruits = new ArrayList<>(fruitIds.size());

for (final var id : fruitIds) {
    fruits.add(FruitFactory.instance(id));
}

class FruitFactory {
    public static Fruit instance(int id) {
        Fruit fruit = new Fruit();
        fruit.setId(id);
        return fruit;
    }
}

If you are only creating instances of Fruit in a single place in your code then the above would be of little use. In that case I would just stick with what you have.

Using the above, the stream solution would be

List<Fruit> fruits = 
     fruitIds.stream().map(FruitFactory::instance).toList();

And with a constructor

List<Fruit> fruits = fruitIds.stream().map(Fruit::new).toList();