Is this correct usage of lambdas in Java 8?

Question

final List<String> userIds = request.getUserIds();
final List<String> keys = userIds.stream().map(p -> { 
    return removePrefix(p); 
}).collect(Collectors.toList());

Basically, every key in the list of userIds contains a prefix "_user" which I want to remove for every key. So, I am invoking the removePrefix function on each item of the list and storing that result in another list called "keys"

Answer 1

Yes it's fine although you could make it a little shorter and more readable with a method reference and a static import:

final List<String> keys = userIds.stream()
                                 .map(this::removePrefix)
                                 .collect(toList());

Answer 2

The answer of @assylias is nice, but if you are not worried about modifying the list in place (and that you are allowed to modify it via its ListIterator#set method), a good alternative could be to use replaceAll :

final List<String> userIds = request.getUserIds();
userIds.replaceAll(this::removePrefix);

replaceAll works here because your function is a function from T to T (where T is String in your case), so basically a UnaryOperator , which is a Function<T,T> .

If the mapping you wanted to apply would have been from a type T to U, then getting the list's stream and doing the mapping via the Stream#map method (like you did) is the standard idiom.