通用类型的元素的ArrayList-可以完成吗？

Question

I have this interface:

public interface Carriable
{
    public abstract String getName();
}

And the 2 classes that implement this interface : Passenger and CargoItem

public class Passenger implements Carriable 
public class CargoItem implements Carriable

I also have a class Compartment that can be either of type Passenger or type CargoItem, not both and has some carriables(passengers/cargoItems)

public class Compartment<T extends Carriable>
{
    ...    
    private ArrayList<T> allCarriables;
    ...
}

All these are specifies clearly in the problem statemnet. Now I want to create a Ship class that has "some unique linked compartment". I would want to write

public class Ship
{
 private Set<Compartment<T extends Carriable>> allComaprtments;
}

in order to be able to add compartments of 2 different types. Why is it not allowed and what would be another approach?

UPDATE :
I want to be able to add compartments of a specific type, for example:

Compartment<Passenger> oneComp= new Compartment();  

this.allComaprtments.add(oneComp);

Answer 1

So long as you have no real interest in getting the subtypes you get back, you can use this instead:

public class Ship
{
 private Set<Compartment<? extends Carriable>> allComaprtments;
}