Book Image

Reactive Programming in Kotlin

By : Rivu Chakraborty
Book Image

Reactive Programming in Kotlin

By: Rivu Chakraborty

Overview of this book

In today's app-driven era, when programs are asynchronous, and responsiveness is so vital, reactive programming can help you write code that's more reliable, easier to scale, and better-performing. Reactive programming is revolutionary. With this practical book, Kotlin developers will first learn how to view problems in the reactive way, and then build programs that leverage the best features of this exciting new programming paradigm. You will begin with the general concepts of Reactive programming and then gradually move on to working with asynchronous data streams. You will dive into advanced techniques such as manipulating time in data-flow, customizing operators and provider and how to use the concurrency model to control asynchronicity of code and process event handlers effectively. You will then be introduced to functional reactive programming and will learn to apply FRP in practical use cases in Kotlin. This book will also take you one step forward by introducing you to Spring 5 and Spring Boot 2 using Kotlin. By the end of the book, you will be able to build real-world applications with reactive user interfaces as well as you'll learn to implement reactive programming paradigms in Android.
Table of Contents (20 chapters)
Title Page
About the Author
About the Reviewers
Customer Feedback

Varieties of Subject

As we mentioned earlier, there are a lot of varieties available for Subjects. As we have gained some grip in Subject, let's now dive into varieties of Subject to understand it better. So, these are some of the most useful and important varieties of Subject, which we will discuss here:

  • AsyncSubject
  • PublishSubject
  • BehaviorSubject
  • ReplaySubject

Understanding AsyncSubject

AsyncSubject only emits the last value of the source observable (Observable it listens on), and the last emission only. To say things more clearly, AsyncSubject will emit the last value it got, and will emit it only one time.

This is a marble diagram for AsyncSubject, which has been taken from ReactiveX documentation (

Let's consider the following code example:

    fun main(args: Array<String>) { 
      val observable = Observable.just(1,2,3,4)//1 
      val subject = AsyncSubject.create<Int>()//2