Convert List of one type to Array of another type using Java 8

Question

I need to convert List of string to Array of userdefinedType and for array I need to convert string to long.

I have achieved the same using below approach to achieve it

TeamsNumberIdentifier[] securityPolicyIdArray = securityPolicyIds.stream()
                .map(securityPolicy -> new TeamsNumberIdentifier(Long.valueOf(securityPolicy)))
                .collect(Collectors.toCollection(ArrayList::new))
                .toArray(new TeamsNumberIdentifier[securityPolicyIds.size()]);

Is there any better approach to convert this?

Answer 1

You don't need to create a temporary ArrayList. Just use toArray() on the stream:

TeamsNumberIdentifier[] securityPolicyIdArray = securityPolicyIds.stream()
            .map(securityPolicy -> new TeamsNumberIdentifier(Long.valueOf(securityPolicy)))
            .toArray(TeamsNumberIdentifier[]::new);

But in general, I would tend to avoid arrays in the first place, and use lists instead.

Answer 2

I would write it like this:

securityPolicyIds.stream()
                 .map(Long::valueOf)
                 .map(TeamsNumberIdentifier::new)
                 .toArray(TeamsNumberIdentifier[]::new);