Java 8 Streams, example that not compile

Question

My question is short, why does it not compile?

final ArrayList <Integer> list = IntStream.rangeClosed(1, 20).boxed().collect(Collectors.toList());

The problem occurs in Collectors.toList() part.

Answer 1

Collectors.toList() returns some List implementation that doesn't have to be ArrayList, and probably isn't.

Try

final List <Integer> list = IntStream.rangeClosed(1, 20)
                                     .boxed()
                                     .collect(Collectors.toList());

You can use collect(Collectors.toCollection(ArrayList::new)) if you specifically need an ArrayList.

final ArrayList <Integer> list = IntStream.rangeClosed(1, 20)
                                          .boxed()
                                          .collect(Collectors.toCollection(ArrayList::new));