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

Suppressing operators


There are a number of operators that will suppress emissions that fail to meet a specified criterion. These operators work by simply not calling the onNext() function downstream for a disqualified emission, and therefore does not go down the chain to Observer. We have already seen the filter() operator, which is probably the most common suppressing operator. We will start with this one.

filter()

The  filter() operator accepts Predicate<T> for a given Observable<T>. This means that you provide it a lambda that qualifies each emission by mapping it to a Boolean value, and emissions with false will not go forward.

For instance,  you can use filter() to only allow string emissions that are not five characters in length:

import io.reactivex.Observable;

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

      Observable.just("Alpha", "Beta", "Gamma", "Delta", "Epsilon")
      .filter(s -> s.length() != 5)
      subscribe(s -> System.out.println...