Question

EDIT: forgot a line of code that is likely causing the issue (night’s sleep helped 😉

Ok it’s late so I’m probably missing something fundamental here but this is my issue:

I have query my db and get a data set that looks like this:

retail_store_id basket_item_id  price_txt
1           2       8.99
1           1       1.5
1           6       11.09
1           4       3.99
2           6       10.99
2           2       9
2           1       1.79
3           4       2.99
3           1       1.5
4           1       1.39
4           6       9.99
4           4       3.5
4           2       7.99

Now I have a Store class which contains a List items and each basketitem has a price.

now to get that into my dto’s I do this:

    Map<Integer, Store> shoppedBasketHash = new HashMap<Integer, Store>();
    while (rs.next()){
            int storeID = rs.getInt("retail_store_id");

            basketItem = new BasketItem();
                            basketItem = GlobalHashOfItems.get(rs.getInt("basket_item_id"));
            basketItem.price = new BigDecimal(rs.getString("price_txt"));

            if(shoppedBasketHash.containsKey(storeID)){
                shoppedBasketHash.get(storeID).items.add(basketItem);                   
            }else{

                Store store = new Store();
                store.retailStoreID = rs.getInt("retail_store_id");

                store.items = new ArrayList<BasketItem>();
                store.items.add(basketItem);

                shoppedBasketHash.put(storeID, sb);
            }
        }
   return new ArrayList<Store>(shoppedBasketHash.values());

Now for some reason, later on when I take this list:

    for(Store s: listOfStores){
        for(BasketItem b: s.items){
                         System.out.println(b.price);
                    }
        }

I get this:
9.99

3.5

7.99

1.39

1.39

9.99

7.99

1.39

3.5

3.5

7.99

1.39

9.99

Which is not the same list of prices I took in. What am I doing wrong?

I realize now the issue is in the
basketItem = GlobalHashOfItems.get(rs.getInt(“basket_item_id”));

I have a hash of items (without prices) that contains other item info not pulled from the DB that I need to use then add the price too. But it’s not copying by value it’s using an object reference. How do I make basketItem get assigned to the value of the GlobalHashOfItems item and not a reference?

Answer 1

Your problem is that HashMap does not preserve insertion/iteration order when it is converted into an ArrayList to return from your method.

You can solve this by building the ArrayList to return while using the Map for addition.

Another way would be to use a LinkedHashMap which does preserve insertion/iteration order.