Why do we have to cast the List returned by Collectors.toList() to List<Integer> even though the elements of the Stream are already mapped to Integer?

I'm mapping a raw Stream to a Stream<Integer> and then collect the elements to a List<Integer>.

Why do I have to cast the result of collect(Collectors.toList()) to List<Integer> if my mapper - .map(str -> ((String)str).length()) - already maps to Integer?

My code:

List list = Arrays.asList("test", "test2");
List<Integer> lengths = (List<Integer>) list.stream()
                                            .map(str -> ((String)str).length())
                                            .collect(Collectors.toList());

If I don't use a raw List, there's no need to cast:

List<String> list = Arrays.asList("test", "test2");
List<Integer> lengths = list.stream()
                            .map(str -> str.length())
                            .collect(Collectors.toList());