CODEWITHSUNDEEP
javajava-8java-streamjava-9
Niraj Sonawane
Niraj Sonawane

Reputation: 11055

Remove all Optional empty/null values from arraylist in java

I need to remove all empty/null values from List<Optional<String>>.

Example:

List<Optional<String>> list = new ArrayList<>();

list.add(Optional.empty());
list.add(Optional.of("Str1"));
list.add(Optional.of("Str2"));
list.add(Optional.of("Str3"));
list.add(Optional.of("Str4"));
list.add(Optional.of("Str5"));
list.add(Optional.empty());
list.add(Optional.ofNullable(null));

Currently, I'm using one of the below approaches:

Way 1: 

List<String> collect = list.stream()
                   .filter(Optional::isPresent)
                   .map(obj ->obj.get())
                   .collect(Collectors.toList());

Way 2: 

List<Optional<String>> emptlist = new ArrayList<>();
emptlist.add(Optional.empty());
list.removeAll(emptlist);

Is there any other better way?

Upvotes: 20

Views: 9513

Answers (3)

Sumit Paroothi
Sumit Paroothi

Reputation: 101

For anyone who wants to have a little fun or understand working of Optionals and Streams better (Java 8):

List<String> collect=list.stream().
                                   map(z->z.map(Stream::of)).
                                   flatMap(ox->ox.orElseGet(Stream::empty)).
                                   collect(Collectors.toList());
  1. The first map function converts Optional[String] to Optional [Stream[String]]. A Stream String[Optional [Stream[String]]] is thus passed forward
  2. The "map" part of flatmap converts each Optional[Stream[String]] to Stream[String]. All empty Optionals are replaced by an empty Stream. Now we have Stream[Stream[String]].
  3. The "flat" part converts Stream[Stream[String]] to Stream[String].

Upvotes: 1

Naman
Naman

Reputation: 31878

With Java9, you can do this using the newly added Optional::stream API :

List<String> collect = list.stream()
               .flatMap(Optional::stream)
               .collect(Collectors.toList());

This method can be used to transform a Stream of optional elements to a Stream of present value elements.

Sticking with Java8, the Way1 in the question is good enough IMHO -

List<String> collect = list.stream()
               .filter(Optional::isPresent)
               .map(Optional::get) // just a small update of using reference
               .collect(Collectors.toList());

Upvotes: 26

Daniel Taub
Daniel Taub

Reputation: 5369

removeIf is the shortest way to do that :

list.removeIf(x -> !x.isPresent());

Upvotes: 8

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