Converting String Collection to a Map with input as the key mapper

Question

Here's an example:

Map<String, Student> getStudentsById(Collection<String> ids) {

  return ids.stream()
       .collect(Collectors.toMap(<id-here>, id -> new Student(id))

}

I'm not sure how to use Collectors.toMap, so that key is the stream element (here in case the ID), and value is some object constructed from the key.

Does this answer your question? [Convert a Collection to Map> using java 8 streams](https://stackoverflow.com/questions/38947983/convert-a-collection-to-mapstring-collectionstring-using-java-8-streams) — Seba López, Aug 25 '20 at 06:40
@SebastiánLópez No it's not. This question is about using the same input argument as the key mapper. — Gayan Weerakutti, Aug 25 '20 at 06:49

score 1 · Accepted Answer · edited Aug 25 '20 at 06:46

1

You are passing a String and a Student to Collectors.toMap(), when you should be passing a Function<? super String,? extends String> and a Function<? super String,? extends Student>.

It should be:

Map<String, Student> idToStudent = ids.stream()
     .collect(Collectors.toMap(Function.identity(), id -> new Student(id)));

edited Aug 25 '20 at 06:46

Andreas

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answered Aug 25 '20 at 06:36

Eran

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Converting String Collection to a Map with input as the key mapper

1 Answers1