1Item.java

public interface Item {
    void printStructure();
    int weight();
}

2Box.java

public record Box(int weight) implements Item {
    @Override
    public int weight() {
        return weight;
    }

    @Override
    public void printStructure() {
        System.out.print("*Box");
    }
}

3Container.java

public record Container(Item[] items) implements Item {
    @Override
    public int weight() {
        var itemsWeight = Arrays.stream(items).mapToInt(Item::weight).sum();
        return 2 + itemsWeight;
    }

    @Override
    public void printStructure() {
        System.out.print(" Container[");
        for (Item item : items) {
            item.printStructure();
        }
        System.out.print("]");
    }
}

4Main.java

    public static void main(String[] args) {
        var ensemble = new Container(
                new Item[]{
                        new Box(2),
                        new Container(new Item[]{
                                new Box(3),
                                new Box(4)}
                        )});

        ensemble.printStructure();
        System.out.println();
        System.out.println("Total weight is: " + ensemble.weight());
    }
// Container[*Box Container[*Box*Box]]
//Total weight is: 13