Question

I have two Collection objects, I want to associate each object of these two in a readable way (HashMap, Object created on purpose, you choose).

I was thinking of two loops one nested into the other, but maybe it’s a well known problem and has a commonly understandable solution…

What if the number of Collection objects raises above two?

EDIT after Joseph Daigle comment: The items of the Collection objects are all of the same type, they are rooms of hotels found to be bookable under certain conditions.

Collection<Room> roomsFromA = getRoomsFromA();
Collection<Room> roomsFromB = getRoomsFromB();
for(Room roomA : roomsFromA){
    for(Room roomB : roomsFromB){
        //add roomA and roomB to something, this is not important for what I need
        //the important part is how you handle the part before
        //especially if Collection objects number grows beyond two
    }
}

EDIT 2: I’ll try to explain better, sorry for the question being unclear.
Follows an example:
A user requests for a double and a single room.
The hotel has 3 double and 4 single rooms available.

I need to associate every “double room” to every “single room”, this is because each Room has its own peculiarity say internet, a more pleasant view, and so on. So i need to give the user all the combinations to let him choose.

This is the simple case, in which only two Collection of Room objects are involved, how do you manage the problem when say both hotel and user can offer / request more Room types?

Answer 1

What you are trying to do here is to get all possible permutations of choosing X from a set of Y. This is a well known problem in discrete mathematics and I think it is just called Combinatorial Mathematics.

To solve your problem you need to create a super collection containing all your Room types. If this is an array or a List you can then use this example to calculate all possible ways of choosing X from the set of Y. The example will give you the indices from the list/array.