Book Image

Learning RxJava

By : Thomas Nield
Book Image

Learning RxJava

By: Thomas Nield

Overview of this book

RxJava is a library for composing asynchronous and event-based programs using Observable sequences for the JVM, allowing developers to build robust applications in less time. Learning RxJava addresses all the fundamentals of reactive programming to help readers write reactive code, as well as teach them an effective approach to designing and implementing reactive libraries and applications. Starting with a brief introduction to reactive programming concepts, there is an overview of Observables and Observers, the core components of RxJava, and how to combine different streams of data and events together. You will also learn simpler ways to achieve concurrency and remain highly performant, with no need for synchronization. Later on, we will leverage backpressure and other strategies to cope with rapidly-producing sources to prevent bottlenecks in your application. After covering custom operators, testing, and debugging, the book dives into hands-on examples using RxJava on Android as well as Kotlin.
Table of Contents (21 chapters)
Title Page
Credits
About the Author
Acknowledgements
About the Reviewers
www.PacktPub.com
Customer Feedback
Preface

Reducing operators


You will likely have moments where you want to take a series of emissions and consolidate them into a single emission (usually emitted through a Single). We will cover a few operators that accomplish this. Note that nearly all of these operators only work on a finite Observable that calls onComplete() because typically, we can consolidate only finite datasets. We will explore this behavior as we cover these operators.

count()

The simplest operator to consolidate emissions into a single one is count(). It will count the number of emissions and emit through a Single once onComplete() is called, shown as follows:

import io.reactivex.Observable;

public class Launcher {
      public static void main(String[] args) {

        Observable.just("Alpha", "Beta", "Gamma", "Delta", "Epsilon")
          .count()
          .subscribe(s -> System.out.println("Received: " + s));

      }
}

The output of the preceding code snippet is as follows:

    Received: 5

Like most reduction operators...