The Flow.Processor interface can serve as both Subscriber and Publisher. The implementation is provided here:

static interface Flow.Processor<T,R> extends Flow.Subscriber<T>, Flow.Publisher<R>

This interface takes two arguments—the subscribed item type <T> and the published item type <R>. It does not have its own methods, but does inherit the following method from java.util.concurrent.Flow.Publisher:

void subscribe(Flow.Subscriber<? super T> subscriber)

Flow.Processor also inherits the following methods from java.util.concurrent.Flow.Subscriber interface:

• void onComplete()
• void onError(Throwable throwable)
• void onNext(T item)
• void onSubscribe(Flow.Subscription subscription)