CODEWITHSUNDEEP
javalistjava-8java-stream
principal-ideal-domain
principal-ideal-domain

Reputation: 4266

List<String> to List<Integer> using Integer foo(String s)

I've got a list List<String> (list1) and a function Integer foo(String s). Using the power of Java 8 I want to convert list1 to a List<Integer> by applying foo to each item of list1. The following code works but has a little problem:

List<Integer> list2 = list1.stream().mapToInt(s -> foo(s)).boxed().collect(Collectors.toList());

When fooreturns null for some element of list1 a NullPointerExceptionis thrown. Additionally my solution looks a little bit inconvenient. So is there a better one?

Upvotes: 2

Views: 116

Answers (2)

Paul Boddington
Paul Boddington

Reputation: 37645

As an alternative to the answer already given, you can do this:

List<Integer> list2 = new ArrayList<>();
list1.forEach(s -> list2.add(foo(s)));

Upvotes: 1

mkobit
mkobit

Reputation: 47249

If you are mapping it to an Integer, I don't see the need to use mapToInt and then use boxed.

Instead, you could simple use map and then filter to exclude the nulls.

List<Integer> list2 =
    list1.stream()
       .map(s -> foo(s))
       .filter(Objects::nonNull)
       .collect(Collectors.toList());

If you want to keep the nulls in the list, simply remove the filter

List<Integer> list2 =
    list1.stream()
       .map(s -> foo(s))
       .collect(Collectors.toList());

Upvotes: 5

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