Can I access the value of a previous lambda in a stream chain?

Question

I have this stream code, which does not compile:

itemList.stream()
    .map(im -> item2dogsMap.get(im.getEan()))
    .flatMap(List<Dog>::stream)
    .forEach(d -> System.out.println("item" + im + " with dog " + d));

The problem is that in the forEach statement I need im and d. But it cannot resolve im here.

I could create an ItemAndDog class taking the two values and do a new in the map statement. But that looks like overkill to me. Is there a way to do this without creating an extra class?

Answer 1

You can not. If you convert your lambdas to anonimous inner classes, you will see, the variables which you wanted to use are out of scope.

Answer 2

You can solve the problem creating the resulting string inside the flatMap where you will have an access to both variables like this:

itemList.stream()
    .flatMap(im -> item2dogsMap.get(im.getEan()).stream()
        .map(d -> "item" + im + " with dog " + d))
    .forEach(System.out::println);