Question about MapStream.intoMulti

[François Sarradin]

Hi all,

I would like to know what is the purpose of the method MapStream.intoMulti?
Is it convert a MapStream into a Map of Collection[s] ?

Here is an example that I have tried with this method:

    public static Map<DevelopmentStage, Collection<Person>>
distribute(Iterable<Person> persons) {
        return persons
                     .groupBy(Age::getDevelopmentStage)
                     .intoMulti(
                         new HashMap<DevelopmentStage,
Collection<Person>>(),
                         () -> new ArrayList<Person>());
    }

But this code generates this error:

error: method intoMulti in interface MapStream<K,V> cannot be applied to
given types;
required: A,Factory<C>
found: HashMap<DevelopmentStage,Collection<Person>>,lambda
reason: invalid inferred types for A,C
reason: inferred type does not conform to declared bound(s)
inferred: HashMap<DevelopmentStage,Collection<Person>>
bound(s): Map<? super DevelopmentStage,ArrayList<Person>>
where A,C,V,K are type-variables:
A extends Map<? super DevelopmentStage,C> declared in method
<A,C>intoMulti(A,Factory<C>)
C extends Collection<? super V> declared in method
<A,C>intoMulti(A,Factory<C>)
V extends Object declared in interface MapStream
K extends Object declared in interface MapStream

Am I wrong ? Why the lambda expression is not inferred into
Factory<Collection<Person>> ?

Thanks,

Francois Sarradin