Not able to convert a value from List<Long> at ith position to long

May be this is very simple but I am struggling a lot from hours. I have a list of Long which has got some 100 values in it. I have to loop through this list and have to get the value at ith position in a Long variable. 

List<Long> dmrIds = (List<Long>)q.getResultList();

is my list which is fetching data from DB. I am using a for loop 

for(int i=0;i<dmrIds.size();i++){
   Long dmrId = dmrIds.get(i).longValue();
   ..........
}

When I try to convert into Long, it is giving:

`java.math.bigDecimal` can't be converted into `java.lang.Long`

I am unable to crack it. Please help.

Jon Skeet
people
quotationmark

Even though you're casting the result of q.getResultList() to a List<Long>, that cast doesn't really check that it's a List<Long>... because at execution time, it's really just a List. (This is due to type erasure in Java generics.)

It sounds like really it's a List<BigDecimal>... so either you need to change what getResultList() does, or you need to handle the fact that it's a List<BigDecimal> and deal with the BigDecimal values.

You can validate this by iterating over each element and just printing out the type:

List<?> results = (List<?>) q.getResultList();
for (Object result : results) {
     System.out.println(result.getClass());
}

Or look at it in a debugger, of course.

To get all the values as long, you just need to call longValue():

List<BigDecimal> results = (List<BigDecimal>) q.getResultList();
for (int i = 0; i < results.size(); i++) {
    long result = results.get(i).longValue();
    // ...
}

(If you don't actually need the index, I'd suggest using an enhanced for loop instead of explicitly getting each item by index though.)

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