Iterate through list of object array

Question

I'm making query using native sql with following code

private <T> List<T> executeNativeQuery(String queryString,
        Map<String, Object> param, Class<T> clazz) {
    Query query = entityManager.createNativeQuery(queryString);
    if (param != null && param.size() > 0) {
        for (Map.Entry<String, Object> entry : param.entrySet()) {
            query.setParameter(entry.getKey(), entry.getValue());
        }
    }
    List<T> resultList = query.getResultList();
    return resultList;
}

And getting following database result.

VendorName | IncidentID | IncidentStatus | IncidentDate
-------------------------------------------------------
XYZ        | 100        |     Open       | 02-JUN-2011    
ABC        | 101        |     Closed     | 03-JUN-2011  
MNP        | 102        |     Open       | 01-JUN-2011  
LPQ        | 103        |     Open       | 01-APR-2011

To iterate this result, i'm using following approach

 Iterator iter=resultList.iterator();
    while (iter.hasNext()) {
        Object[] result= (Object[]) iter.next();
        System.out.println("Vendor Name-->" +result[0]);
 }

Is there any better way to iterate through the list ?

You should use Iterator<Object[]>, not bare Iterator. But see the answers for better ideas. — David Conrad
– David Conrad, Commented Jun 20, 2013 at 19:12
@DavidConrad Thanks for pointing out. But definition for this function is - Iterator<E> iterator(). It wouldn't be applied to an array. How can we handle this ? — Pankaj
– Pankaj, Commented Jun 20, 2013 at 22:10
@Pankaj Sorry, what is the type T of the List<T> that it is returning? Or, to put it another way, what is the type of resultList? You are already casting iter.next() to Object[], so it must be an Iterator of either Object[] or some other array type, right? — David Conrad
– David Conrad, Commented Jun 21, 2013 at 16:44
@DavidConrad You're right David. I was passing String.class as type which was causing this issue. Thanks for pointing out. — Pankaj
– Pankaj, Commented Jun 24, 2013 at 21:31

Costi Ciudatu · Accepted Answer · 2013-06-20 19:07:36Z

7

One "better way" (java 5+ for-each) will actually translate to what you've shown, using an iterator, but the syntax is nicer:

for (Object[] result : resultList) {
    // ...

The other "better way" relies on the fact that you know the list size and you can use a counter in a for loop:

for (int i = 0; i < resultList.size(); i++) {
    Object[] result = resultList.get(i);
    // ... the rest ...

To sum up, there are several ways to iterate through a list, but it's arguable that there are "better" ways: it's a matter of use-case (if you're using that i counter for other things as well or you're using the iterator to also remove some elements from the list) or simply a matter of taste (low-level vs. syntax-sugar).

edited Jun 20, 2013 at 19:07

answered Jun 20, 2013 at 19:02

Costi Ciudatu

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mokuril · Accepted Answer · 2013-06-20 20:12:34Z

0

In Java 5+ the for each loop is the preferred way

for (Object[] result : resultList) {...}

This could have better performance sometimes because it calculates collection size once. Also, when using a traditional for loop and doing a nested iteration over two collections, you might create a bug. Joshua Bloch mentions it in his book 'Effective Java', item 46. A bit more detailed ofcourse.

http://www.amazon.com/Effective-Java-Edition-Joshua-Bloch/dp/0321356683/ref=dp_ob_title_bk

edited Jun 20, 2013 at 20:12

answered Jun 20, 2013 at 19:46

mokuril

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