import com.google.gson.Gson;
import com.google.gson.GsonBuilder;

import java.util.ArrayList;

class Convoy {
    private ArrayList<Vehicle> vehicles = new ArrayList<>();

    public void add(Vehicle vehicle) {
        vehicles.add(vehicle);
    }
}

abstract class Vehicle {
    private int maxSpeed;
    //...
}

class Car extends Vehicle {
    private int cargoCapacityInLiter;
    //...
}

class Plane extends Vehicle {
    private int wingspanInMeter;
    //...
}

class Bicycle extends Vehicle {
    private int frameHeight;
    //...
}

public class Main {
    public static void main(String[] args) {
        RuntimeTypeAdapterFactory<Vehicle> vehicleAdapterFactory = RuntimeTypeAdapterFactory.of(Vehicle.class, "type")
                .registerSubtype(Car.class, "Car")
                .registerSubtype(Plane.class, "Plane")
                .registerSubtype(Bicycle.class, "Bicycle");

        Gson gson = new GsonBuilder()
                .registerTypeAdapterFactory(vehicleAdapterFactory)
                .create();

        String carJson = gson.toJson(new Car(), Vehicle.class);
        String planeJson = gson.toJson(new Plane(), Vehicle.class);
        String bicycleJson = gson.toJson(new Bicycle(), Vehicle.class);

        System.out.println(carJson);
        System.out.println(planeJson);
        System.out.println(bicycleJson);

        Convoy convoy = new Convoy();
        convoy.add(new Car());
        convoy.add(new Plane());
        convoy.add(new Bicycle());

        String convoyJson = gson.toJson(convoy);

        System.out.println(convoyJson);
    }
}