import java.util.List; | |
import java.util.Map; | |
class Collector<C> { | |
} | |
interface Function<T, R> { | |
R apply(T t); | |
} | |
final class Collectors { | |
public static <T> | |
Collector<List<T>> toList() { | |
return null; | |
} | |
public static <T1, K1> Collector<Map<K1, List<T1>>> groupingBy(Function<T1, K1> classifier) { | |
return groupingBy(classifier, toList()); | |
} | |
public static <T, K, D> Collector<Map<K, D>> groupingBy(Function<T, K> classifier, | |
Collector<D> downstream) { | |
return null; | |
} | |
} |