CODEWITHSUNDEEP
javalistdictionarystreamcollectors
MiketheCalamity
MiketheCalamity

Reputation: 1269

java - Stream collect toMap - Type mismatch

I am trying to collect a List of Collections into a Map, where the key is the index from the original list and the value is the collection. I tried the following, but I get a Type mismatch error: Type mismatch: cannot convert from Map<Object,Object> to Map<Integer,Collection<String>>

My code:

public Map<Integer, Collection<String>> myFunction(final List<Collection<String>> strs) {
    return strs.stream().collect(Collectors.toMap(List::indexOf, v -> v)); // Error here
}

Any suggestions?

Upvotes: 2

Views: 2215

Answers (2)

Tonney Bing
Tonney Bing

Reputation: 230

you can do like this:

List<Collection<Integer>> list = ...;
Map<Integer, Collection<Integer>> collect = IntStream.range(0, list.size())
        .boxed()
        .collect(Collectors.toMap(Function.identity(), v -> list.get(v)));

Upvotes: 1

ernest_k
ernest_k

Reputation: 45339

You have a compilation error: Cannot make a static reference to the non-static method indexOf(Object) from the type List.

If you correct it as below, it will compile:

return strs.stream().collect(Collectors.toMap(coll -> strs.indexOf(coll), v -> v));

Or, using a method reference:

return strs.stream().collect(Collectors.toMap(strs::indexOf, v -> v));

Upvotes: 1

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