Book Image

Learning RxJava - Second Edition

By : Nick Samoylov, Thomas Nield
Book Image

Learning RxJava - Second Edition

By: Nick Samoylov, Thomas Nield

Overview of this book

RxJava is not just a popular library for building asynchronous and event-based applications; it also enables you to create a cleaner and more readable code base. In this book, you’ll cover the core fundamentals of reactive programming and learn how to design and implement reactive libraries and applications. Learning RxJava will help you understand how reactive programming works and guide you in writing your first example in reactive code. You’ll get to grips with the workings of Observable and Subscriber, and see how they are used in different contexts using real-world use cases. The book will also take you through multicasting and caching to help prevent redundant work with multiple Observers. You’ll then learn how to create your own RxJava operators by reusing reactive logic. As you advance, you’ll explore effective tools and libraries to test and debug RxJava code. Finally, you’ll delve into RxAndroid extensions and use Kotlin features to streamline your Android apps. By the end of this book, you'll become proficient in writing reactive code in Java and Kotlin to build concurrent applications, including Android applications.
Table of Contents (22 chapters)
1
Section 1: Foundations of Reactive Programming in Java
5
Section 2: Reactive Operators
12
Section 3: Integration of RxJava applications
Appendix B: Functional Types
Appendix E: Understanding Schedulers

Grouping operators

To group emissions by a specified key into separate observables is a powerful operation. This can be achieved by calling the groupBy(Function<T,K> keySelector) operator, which accepts a function that maps each emission to a key. It will then return an Observable<GroupedObservable<K,T>>, which emits a special type of Observable called GroupedObservable. The GroupedObservable<K,T> class is just like any other Observable, but it has the key K value accessible as a property. It emits T type values 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.rxjava3.core.Observable;
import io.reactivex.rxjava3.observables.GroupedObservable;

public class...