How to add all Strings to a ArrayList from a List of objects most efficient?

Question

NB: Please edit the title if you could write it better.. I've no idea how to explain it better..

Over to the problem: I'm using autocomplete in a javafx form and need to get all the customers firstName into a list for Strings. I've used JPA to get all of the customers from the database. So i'm a bit worried about the speed of my code.. You see why..

Code example:

public static List<String> getAllFirstNamesCustomer() {
        List<String> names = new ArrayList<>();
        for (Customer c : CustomerBean.getAllCustomers()) {
            names.add(c.getCName());
        }
        List<String> output =
            new ArrayList<>(new LinkedHashSet<>(names));
        return output;

    }  

EDIT:

Think i found a better way:

public static List<String> getAllFirstNamesCustomer() {
    return em.createNativeQuery("select DISTINCT cname from customer").getResultList();  
}

Answer 1

Good option would be for the database driver to stream the data. A workaround and with a larger customer data set, you can leverage Java 8's parallel streams which takes advantage of all cores of the CPU, with one liner

List<String> names = CustomerBean.getAllCustomers().parallelStream().map(c.getCName()).collect(toList());