How to Iterate Two Lists and compare the items within?

Question

I'm almost at the end of my final project in the university, I'm trying to control my inStock with my current Stock of articles.

My stock contains the following attributes:

int idMercaderia;
int cantidad;
int idSucursal;

I have two lists that contains Inventario type POJOs:

List <Inventario> stock = new InventarioDAO().findAll();
List <Inventario> inStock = new ArrayList <Inventario>();

Before persist in the database, I want to compare the attribute idMercaderia in both of 'em, if they're the same don't create another entry and just add the quantity cantidad to the current stock and do a saveOrUpdate() if not just create another entry.

I'm really stuck in this part and currently run out of ideas after trying iterate both Lists but I can't figure out the stock thingy.

Any help/code will be really appreciated.

Have you implemented an equals method in Inventario. If so please show the logic of it. — shazin, Oct 23 '13 at 07:04
`Inventario` has been generated using Reverse Engineering with MyEclipse, so I only got the Hibernate DAO's (`save()`, `delete()`, `findById()`, etc.) — Felipe Rodriguez, Oct 23 '13 at 07:09
org.apache.commons.beanutils [check this ](http://stackoverflow.com/questions/6099040/find-out-the-differences-between-two-java-beans-for-version-tracking/6099386#6099386) used for comparing beans — jos, Oct 23 '13 at 13:52
@user2334391 thanks for sharing this, i'm enconding this right now inside my iteration. — Felipe Rodriguez, Oct 23 '13 at 14:50

score 1 · Accepted Answer · answered Oct 23 '13 at 07:09

1

you need to implement an equals() method if not already happened in the Inventario to compare idMercaderia in there. then

for(Inventario item: stock){
   if(inStock.contains(item)){
       item.cantidad++;  
   }
}

answered Oct 23 '13 at 07:09

Roman K

3,309
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This is one possible solution but makes the `equals` very context specific and hides a bit the logic in my opinion. It is also a possible source of future bugs, because someone might change the `equals` method (if we think of this as an enterprise application). So good unit testing is necessary here. – Kai Oct 23 '13 at 07:15
Gonna try this, but trying to `item.getCantidad()` `++` will be my problem, thank you. – Felipe Rodriguez Oct 23 '13 at 07:29
@user714965 yes it hides the logic a bit, but if the `idMercaderia` is the unique identifier, there should be no problem. it would be better if java would have an Comparator-like approach for this or you have to use java 8 ;) – Roman K Oct 23 '13 at 07:30

Kai · Answer 2 · 2013-10-23T07:25:14.393

1

Create a Map<Integer, Inventario> of your first list to map an idMercaderia to one Inventario. Then iterate your second list and check for each item the corresponding one in the map.

Map<Integer, Inventario> map = new HashMap<Integer, Inventario>();
for (Inventario item : stock) {
   map.put(item.getIdMercaderia(), item);
}

and

for (Inventario item : inStock) {
   int idMercaderia = map.getIdMercaderia();
   Inventario inventario = map.get(idMercaderia);
   if (inventario == null) {
      // error handling
      continue;
   }
   if (item.getCantidad() == inventario.getCantidad() {
      // handle 
   }
}

edited Oct 23 '13 at 07:25

answered Oct 23 '13 at 07:19

Kai

38,985
14
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This makes senses to my toughs, I changed the `map.put(item.getIdMercaderia(), item)` to `map.put(item.getMercaderia().getId(), item)` but in the Iteration of my second List I can't afford to do `map.getIdMercaderia()`. only map methods are shown, any clue on this? – Felipe Rodriguez Oct 23 '13 at 07:43
That's how a [Map](http://docs.oracle.com/javase/7/docs/api/java/util/Map.html) works. You `put` a key/value pair in and call `get(key)` to retrieve the value. So in your case `map.get(item.getMercaderia().getId())` will return the `item`. – Kai Oct 23 '13 at 07:48

How to Iterate Two Lists and compare the items within?

2 Answers2