[COLLECTIONS-666] org.apache.commons.collections4.ListUtils.union(List, List) should pre-allocate result list

• Type: Improvement
• Status: Closed
• Priority: Trivial
• Resolution: Fixed
• Affects Version/s: 4.2
• Fix Version/s: 4.2
• Component/s: List
• Assignee: Unassigned
• Reporter: David Mollitor
• Created: 31/Dec/17 03:36
• Updated: 31/Dec/17 19:17
• Resolved: 31/Dec/17 06:17

Description

public static <E> List<E> union(final List<? extends E> list1, final List<? extends E> list2) {
        final ArrayList<E> result = new ArrayList<E>(list1);
        result.addAll(list2);
        return result;
}

Maybe we should create the result list with the size of list1 + list 2, then perform two add all. This will prevent the ArrayList from being re-sized on the addAll step.