Compare two objects by their field's field

Question

I have a class named House and it has property of type Room.

class House {
   private Room room;
   // getters & setters
}

Room class has a property roomCapacity:

class Room {
   private int roomCapacity;
   // getters & setters
}

I want to sort House HashMap on the base of Room class property named roomCapacity.

Comparator<House> sortByRoomCapacity =
      Comparator.nullsFirst(Comparator.comparing(House::getRoom,
                   Comparator.nullsFirst(Comparator.naturalOrder())));

But for now I am inaccessible to get this property(getRoomCapacity) of Room class House::getRoom

Answer 1

You're almost there.

One more nested comparing method should do the trick:

Comparator<House> sortByRoomCapacity =
         nullsFirst(comparing(House::getRoom, 
                              comparing(Room::getRoomCapacity, 
                                        nullsFirst(naturalOrder()))));