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

Grouping


A powerful operation that you can achieve with RxJava is to group emissions by a specified key into separate Observables. This can be achieved by calling the groupBy() operator, which accepts a lambda mapping each emission to a key. It will then return an Observable<GroupedObservable<K,T>>, which emits a special type of Observablecalled GroupedObservable. GroupedObservable<K,T> is just like any other Observable, but it has the key K value accessible as a property. It will emit the T emissions that are mapped for that given key.

For instance, we can use the groupBy() operator to group emissions for an Observable<String> by each String's length. We will subscribe to it in a moment, but here is how we declare it:

import io.reactivex.Observable;
import io.reactivex.observables.GroupedObservable;

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

        Observable<String> source = 
Observable.just("Alpha", "Beta", "Gamma", "Delta", "Epsilon...