convert list of objects to Map using map/stream/collect

Question

if I have something like this:

List<Person> fetchedPeople

and I want to stream through it and store it into a key-value map where key is the person ID and value is the object itself (here Person)

private Map<String, Person> people;

I tried something like this but it gives me an error:

PersonCache = people.stream()
      .collect(toMap(Person::getID, Person));

Thanks for your help

after reading the suggested answer, it turned out my question is similar to this question https://stackoverflow.com/questions/20363719/java-8-listv-into-mapk-v — samjo, Mar 30 '21 at 15:36

score 2 · Accepted Answer · answered Mar 30 '21 at 15:23

2

I think you want this:

Map<String, Person> result = fetchedPeople.stream().collect(Collectors.toMap(Person::getID, e -> e));

I don't know if there is a way to return "the element itself" without supplying a lambda function that does that, the e -> e part.

answered Mar 30 '21 at 15:23

CryptoFool

[java.util.function.Function#identity](https://docs.oracle.com/en/java/javase/11/docs/api/java.base/java/util/function/Function.html#identity()) – Abra Mar 30 '21 at 15:29
yeah thanks. This worked! – samjo Mar 30 '21 at 15:30

1 Answers1