The introduction of the Processor notion 

We have learned about the primary three interfaces that constitute the Reactive Streams specification. We have also seen how a proposed mechanism may improve the news service that sends news digests via email. However, at the beginning of this section, it was mentioned that there are four core interfaces in the specification. The last one is a combination of Publisher and Subscriber and is called the Processor. Let's take a look at the following implementation's code:

package org.reactivestreams;public interface Processor<T, R> extends Subscriber<T>,                                         Publisher<R> {}

In contrast to the  Publisher and Subscriber, which are start and end points by definition, Processor is designed to add some processing ...

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