Question

This is a Java question.

What is the fastest way to convert a List<?> to a List<ObjectType>? I am aware that this is possible through iteration please exclude that option.

Example by iteration,

final List<ObjectType> targetList = new ArrayList<ObjectType>();
// API returns List<?> so I have no choice.
List<?> resultList = resultSet.getResults(); 

// This is slow. Average list size is 500,000 elements.
while (resultList != null && !resultList.isEmpty()) {
    for (final Object object : resultList) {
        final ObjectType objectType = (ObjectType) object;
        targetList.add(objectType);
    }
    resultSet = someService.getNext(resultSet);
    resultList = resultSet.getList();
}

Thanks.

Answer 1

It’s a bit scary but depending on context you could possibly get away with just casting:

final List<ObjectType> targetList = (List<ObjectType>)problemSolver.getResults();