Java generics incompatible types (no instance(s) of type variable(s) exist)

Sumit :

The question title may seem to be same as some other post but the content is different. So please don't mark it duplicate.

Problem:

I have the below class:

public class SCDTO extends RDTO {
    private List<String> sCPairs = Collections.emptyList();

    public SCDTO(List<String> sCPairs) {
        this.sCPairs = sCPairs;
    }

    //Getter setter

}

I am trying to using the below lambda expression to set the sCPairs.

sCPairsObject.setSCPairs(util.getSCMap().entrySet().stream().
                        filter(entry -> entry.getValue().contains("abc")).collect(Collectors.toCollection(ArrayList<String>::new)));

But I have an compilation error saying:

no instance(s) of type variable(s) exist so that Entry<String, List<String>> conforms to String

util.getSCMap returns Map<String, List<String>>.

Can anyone please explain why this is happening and how to solve it?

Thanks.

Adriaan Koster :

You are streaming entries from the map:

sCPairsObject.setSCPairs(util.getSCMap().entrySet().stream()

Then filtering out some of them:

.filter(entry -> entry.getValue().contains("abc"))

now you need to map the entries to List, for example:

.map(entry -> entry.getValue())

and stream the contents of all these lists as one stream:

.flatMap(List::stream)

Finally collect the values into a list:

.collect(Collectors.toList());