public static IStockRoomItems GetStockRoomItem(StockRoom stockRoom, StockItem stockItem, int quantity)
 {
     if (newStockRoomItem != null)
     {
         return newStockRoomItem;
     }
     else
     {
         return new StockRoomItems(stockRoom, stockItem, quantity);
     }
 }
 public StockRoomItems(StockRoom stockRoom, StockItem stockItem, int quantity)
 {
     this.StockRoom = stockRoom;
     this.StockItem = stockItem;
     this.Quantity = quantity;
 }