Added in API level 30
Summary: Methods

Flow.Publisher

public static interface Flow.Publisher

java.util.concurrent.Flow.Publisher<T>
Flow.Processor<T, R> A component that acts as both a Subscriber and Publisher. 
SubmissionPublisher<T> A Flow.Publisher that asynchronously issues submitted (non-null) items to current subscribers until it is closed. 

A producer of items (and related control messages) received by Subscribers. Each current Subscriber receives the same items (via method onNext) in the same order, unless drops or errors are encountered. If a Publisher encounters an error that does not allow items to be issued to a Subscriber, that Subscriber receives onError, and then receives no further messages. Otherwise, when it is known that no further messages will be issued to it, a subscriber receives onComplete. Publishers ensure that Subscriber method invocations for each subscription are strictly ordered in happens-before order.

Publishers may vary in policy about whether drops (failures to issue an item because of resource limitations) are treated as unrecoverable errors. Publishers may also vary about whether Subscribers receive items that were produced or available before they subscribed.

Summary

Public methods

abstract void subscribe(Subscriber<? super T> subscriber)

Adds the given Subscriber if possible.

Public methods

subscribe

Added in API level 30 
public abstract void subscribe (Subscriber<? super T> subscriber)

Adds the given Subscriber if possible. If already subscribed, or the attempt to subscribe fails due to policy violations or errors, the Subscriber's onError method is invoked with an IllegalStateException. Otherwise, the Subscriber's onSubscribe method is invoked with a new Subscription. Subscribers may enable receiving items by invoking the request method of this Subscription, and may unsubscribe by invoking its cancel method.

Parameters
subscriber Subscriber: the subscriber
Throws
NullPointerException if subscriber is null