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Kotlin and RX Kotlin in Android


In this blog we are going to discuss Kotlin and RXKotlin, so let’s start the topic.

About Kotlin –

Kotlin is a language that combines functional programming and object-oriented programming in a distinctive, unrestricted, and self-sufficient platform. Kotlin is run on a Java virtual machine and it is an open-source programming language.

You can check my other blog regarding Flutter app development .

These are some key points of kotlin –

  • Semicolon isn’t required in kotline programs.
  • Kotlin doesn’t support static member
  • Kotlin supports Lambda Expression
  • In, Kotlin variables of a primitive type 
  • Kotlin doesn’t require any variable data type 
  • Kotlin programs don’t require semicolons 
  • Kotlin has Language scripting capabilities 
  • Kotlin doesn’t offer implicit conversions
  • Kotlin allows users to create an extension
  • Kotlin compilation are fast
  • Kotlin has trimmed code
  • Kotlin combines the oops and functional component

Kotlin History –

There are landmarks and key points of kotlin history.

  • Kotlin was launched his version v1.0 in 2016
  • Google announced his first-class support of Kotlin in Android In 2017
  • Kotlin v1.3 version released in 2018 brings coroutines for asynchronous programming.
  • Google announced Kotlin as its preferred programming language for Android application developers in 2019.

Kotlin Advantage –

Here are some lists of advantages of using kotlin.

  • Kotlin uses the Multiplatform framework and extracts one common codebase.
  • Kotlin has built-in null safety support.
  • In kotlin there is less room for errors.
  • Kotlin divides the large apps into smaller layers.
  • It helps developers to create extension functions.
  • Kotlin is very easy to read and write because it is a statically-typed language.
  • Writing new code in kotlin takes very less time.

Kotlin Disadvantage –

Here are some lists of disadvantages of using kotlin.

  • The Kotlin developer community is very small, that’s why learning material is less.
  • Compilation speed is slower than java.
  • Kotlin is a highly declarative language

About RxKotlin –

Reactive Extensions

Rx stands for Reactive Extensions (Rx), but Rxkotlin is not an implementation of Reactive Extensions, it’s a collection of extension methods. RxKotlin uses the RxJava library with API design.

These are some important points about RxKotlin.

  • As well RxKotlin is dependent on RxJava.
  • RxKotlin does not depend upon RxAndroid.
  • RxAndroid and RxKotlin use RxJava.
  • RxKotlin is only a wrapper over the original RxJava.
  • No need to use RxKotlin if you are using RxJava.
  • You can use RxJava with Kotlin out-of-the-box.
  • Rx Java, Rx Kotlin, or Rx Swift all are the implementation of Reactive Extensions in that particular language.

Setup The RxKotlin –

To set up the project first you need to add the RxKotlin dependencies in your project.

  1. Add the following code in your pom.xml file






  1. Add the following code in build.gradle

   implementation ‘io.reactivex.rxjava2:rxkotlin:2.3.0’

Observables Creation in RxKotlin – 

RxKotlin has a number of extension methods for creating Flowable objects and Observables from collections.

Every array type has a toFlowable() and toObservable() method, it is like the following code.

val observable = listOf(1, 1, 2, 3).toObservable()

observable.test().assertValues(1, 1, 2, 3)

val flowable = listOf(1, 1, 2, 3).toFlowable()

flowable.buffer(2).test().assertValues(listOf(1, 1), listOf(2, 3))

Map and Multimap in Observable and Flowable – 

  • We have Pair instances for Observables or Flowable that produce a Single observable that produces a Map.

val list = listOf(Pair(“a”, 1), Pair(“b”, 2), Pair(“c”, 3), Pair(“a”, 4))

val observable = list.toObservable()

val map = observable.toMap()

assertEquals(mapOf(Pair(“a”, 4), Pair(“b”, 2), Pair(“c”, 3)), map.blockingGet())

  • We use the values associated with a key into a collection for this we use the toMultimap.

val list = listOf(Pair(“a”, 1), Pair(“b”, 2), Pair(“c”, 3), Pair(“a”, 4))

val observable = list.toObservable()

val map = observable.toMultimap()


  mapOf(Pair(“a”, listOf(1, 4)), Pair(“b”, listOf(2)), Pair(“c”, listOf(3))),


Combining Flowables and Observables –

Here we combine the observables with flatMap.

val subject = PublishSubject.create<Observable<String>>()

val observable = subject.mergeAll()


val observable = subject.flatMap { it }

Different Types Values Handling – 

Here we check how you handle the different types of data handling in RxKotlin. It handles the following 2 types of values.

  • cast values from one type to another
  • filter the values that are not of a certain type

val observable = Observable.just<Number>(1, 1, 2, 3)

observable.cast<Int>().test().assertValues(1, 1, 2, 3)

In this article, we have thoroughly reviewed RxKotlin and Kotlin, i think you understand the concept well now