CODEWITHSUNDEEP
javajava-stream
Roma
Roma

Reputation: 333

Java 8 map inner static class property in a non static method

I am trying to get the Java 8 stream equivalent of this old school code.

Set<String> studentNames = new HashSet<String>();
for(Student student : students){
           String name =(student.getName());
            studentNames.add(transform(name));
        }

Student is inner static class while I need to call the api from non static method. transform is a static method. I tried something like this but it doesnt compile.. I get compiler error as static reference cannot be made from non static method...

studentNames = Stream.of(students)
                .filter(Objects::nonNull)
                .map(Student::getName)
                .map(Transformer::transform)
                .collect(Collectors.toSet());

Upvotes: 1

Views: 1751

Answers (2)

Malte Hartwig
Malte Hartwig

Reputation: 4553

As Holger said in his comment, your problem is caused by calling Stream.of(students). If you look at of's signature, you'll see that it expects either a single element or an array of elements. Hence, if you give it a collection, you'll get a stream of collections, not of the collection's elements:

Stream<String>       s1 = Stream.of("hello");
Stream<String>       s2 = Stream.of("hello", "world");
Stream<String>       s3 = Stream.of(new String[] {"hello", "world"});
Stream<List<String>> s4 = Stream.of(Arrays.asList("hello", "world"));
Stream<String>       s5 = Arrays.asList("hello", "world").stream();

Upvotes: 1

Eugene
Eugene

Reputation: 121028

Seems like your problem is here Transformer::transform, you need an actual instance of transformer to make this work. 

Transformer t = new Transformer(...);

list.stream()
            .filter(Objects::nonNull)
            .map(Student::getName)
            .map(t::transform)
            .collect(Collectors.toSet());

Also it looks like Transformer is just a Function<String, String> btw.

Upvotes: 1

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