Question

I’m learning the Play framework. I’m cunfused about three classes which represent a warehouse-stock item-product data model:

public class Product {
  public Long ean; 
  public String name;
  public String description;
  public String toString() {
    return name;
  }
}

public class Warehouse {
  public String name;
  public List<StockItem> stock = new ArrayList<>(); 
  public String toString() {
    return name;
  }
}

public class StockItem {
  public Warehouse warehouse; 
  public Product product; 
  public Long quantity;
  public String toString() {
    return String.format("%d %s", quantity, product);
  }
}

Class Warehouse depends on class StockItem. Class StockItem depends on class Product and Warehouse.

How to understand this kind of relationship?

Answer 1

Warehouse is a container class and it has many items – StockItem‘s. So Warehouse knows about StockItem and every StockItem knows what Warehouse it belongs to.
Something like:

Warehouse warehouse = new Warehouse();
StockItem item1 = new StockItem();
item1.warehouse = warehouse;
warehouse.stock.add(item1);