[CS2103T][W4.3d][Exercise 1] at https://nus-cs2103.github.io/website/

BoxItemCard.java

import java.util.ArrayList;
import java.util.List;

public class Main {
    public static void main(String[] args) {
        Item item1 = new Item();
        Item item2 = new Item();
        Box box1 = new Box(item1);
        Box box2 = new Box(item2);
        item2.setMainCard(new Card());
        item2.addPreviousBox(box1);
        item2.addPreviousBox(box2);
    }
}

class Box{
    private Item item;
    Box (Item item){
        this.item = item;
    }
}

class Item{
    private List<Box> previousBoxes = new ArrayList<>();
    private Card mainCard = null;
    private Card subCard = null;

    void setMainCard(Card card){
        this.mainCard = card;
    }
    
    void setSubCard(Card card){
        this.subCard = card;
    }

    void addPreviousBox(Box previousBox){
        previousBoxes.add(previousBox);
    }
}

class Card{
    
}