[英]Java collect() Stream with generic type
Is there way to collect()
generic items from a stream
? 有没有办法从
stream
collect()
通用项目?
This is what I want to do... 这就是我想做的...
private <T extends Data> List<Response<T>> validateAndGetResponses(List<Response> responses, Class<T> clazz) {
Supplier<List<Response<T>>> supplier = LinkedList::new;
List<Response<T>> list = responses.stream().filter(
response -> clazz.isInstance(getData(response))).collect(Collectors.toCollection(supplier));
return list;
}
This doesn't work, I get 这行不通,我明白了
no suitable method found for collect(....)
So, if the purpose of the code is indeed filtering the Response objects based on the type parameter, a wild guess of the solution could be: 因此,如果代码的目的确实是基于类型参数过滤Response对象,则对解决方案的猜测很可能是:
@SuppressWarnings("unchecked")
private <T extends Data> List<Response<T>> validateAndGetResponses(List<Response<? extends Data>> responses, Class<T> clazz) {
return responses.stream()
.filter(response -> clazz.isInstance(getData(response)))
.map(response -> (Response<T>) response)
.collect(Collectors.toCollection(LinkedList::new));
}
So the problem was I used a raw type List<Response> responses
as an argument, though I really should of used a wildcard boundary, List<Response<? extends Data>> responses
因此,问题是我使用原始类型
List<Response> responses
作为参数,尽管我确实应该使用通配符边界List<Response<? extends Data>> responses
List<Response<? extends Data>> responses
. List<Response<? extends Data>> responses
。
This is the complete method: 这是完整的方法:
@SuppressWarnings("unchecked")
private <T extends Data> List<T> validateAndGetResponses(List<Response<? extends Data>> responses, Class<T> clazz) {
return responses.stream().map(this::getData)
.filter(clazz::isInstance)
.map(r -> (T) r)
.collect(Collectors.toList());
}
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