Java <Streams> How to sort the list of my objects, based on the count of the components of the List

Question

I have 2 classes in Java. One is a Car class that consists of 5 variables. Among them I have a List equipment variable. Another class contains the list of the Car class objects: List carlist.

My task is: I have to sort the list of car object, using Streams in Java based on the amount of the equipment items that the given car have.

How do I do that? I tried to build a separate method to count the items on the list of the object - but then within the Comparator I can't place an Object as an argument of this method.

Here's an excerpt of my code:

private int countEquipmentItems (Car s){
    if (s == null){
        return 0;
    }
    int countEquipment = 0;
    List<String> a = s.getEquipment();
    for (int i = 0; i <a.size() ; i++) {
        countEquipment ++;
    }
    return countEquipment;
}

And I have tried to use this method within the Stream:

public void sortbyEquipment (List<Car> carList){
    carList.stream()
            .sorted(Comparator.comparing(countEquipmentItems(Car s)));
    }
}

I appreciate any help

Answer 1

You don't need that countEquipmentItems method to count the amount of equipment. Just use car.getEquipment().size():

public void sortbyEquipment (List<Car> carList){
    carList.stream()
           .sorted(Comparator.comparing(car -> car.getEquipment().size()))
           ...
}

Of course, you can pass that Comparator directly to Collections.sort(), which will sort the list without having to create a Stream.