How can related data be quickly added to an object or entity?

To quickly add related data to an object or entity in Java, the pattern of "composition" or associations through collections is often used. For example, if you have an Order object and want to add related OrderItems, you can simply add a list of items to the order object:

class Order {
    private List<OrderItem> items = new ArrayList<>();

    public void addItem(OrderItem item) {
        items.add(item);
    }

    public List<OrderItem> getItems() {
        return items;
    }
}

Also, if an ORM (like Hibernate) is used, you can configure relationships between entities using annotations like @OneToMany, @ManyToOne, etc., which will automatically load related data.

If the goal is to add data quickly during runtime, you can use collection add methods or setters for related objects.