Question

What is wrong with below code ?

List<Object[]> currencies = null;
List<String> currencyList = new ArrayList<String>();

//code to fetch currency
String currencySql = "select C.Currency from Currency C";
Query currencyQuery = this.em.createQuery(currencySql);

currencies = currencyQuery.getResultList();

for (Object[] currency : currencies) {    //getting runtime error here
   for (int i = 0; i < currency.length; i++) {
            currencyList.add(currency[i].toString());
        }
    }

Getting runtime error in first line of for loop as:
java.lang.ClassCastException: java.lang.String incompatible with [Ljava.lang.Object;

The code compiles alright.

What is the issue ?

Answer 1

I’m not sure why you are thinking that the Query would return a list of Object arrays.

The query will most likely return a list of Strings (unless the Currency entity contains a Currency object, in which case I’d revisit the data design), so operating under the assumption that this is a scalar query, your code can be simplified to:

String currencySql = "select C.Currency from Currency C";
Query currencyQuery = this.em.createQuery(currencySql);

List<String> currencyList = (List<String>) currencyQuery.getResultList();