Java 8 Stream API : Filter on instance, and cast [duplicate]

问题

This question already has answers here:

Is it possible to cast a Stream in Java 8? (4 answers)

Closed 4 years ago.

I have a list of objects:

List<SomeType> myList;

I want to get a list of sub-types available in this list:

List<SomeChildType> myChildList = myList.stream().filter(e -> e instanceof SomeChildType).collect(??????)

I don't know how to collect to obtain the correct list type.

回答1:

You need to cast the objects:

List<SomeChildType> myChildList = myList.stream()
                                        .filter(SomeChildType.class::isInstance)
                                        .map(SomeChildType.class::cast)
                                        .collect(toList())

来源：https://stackoverflow.com/questions/34879086/java-8-stream-api-filter-on-instance-and-cast