Introduction to RxJava: Why Rx?

This series of articles is intended to familiarize a novice reactive programmer with the power of the RxJava library ˜ — implementing the principles of reactive programming for JVM. This is a translation of an extensive tutorial on RxJava by Criss Frussios based on IntroToRx for Rx.NET.

To follow this tutorial, you will not need knowledge of reactive or functional programming, however, it is assumed that you have basic knowledge of Java.

The material of these articles is designed to read from beginning to end. Its volume is larger than the average tutorial, but smaller than the real book. We will start from the very basics and from section to section we will move on to more advanced scenarios and concepts. Each section was thought of as self-sufficient and concise in order to be able to return to it in the future.

Examples for these materials are available in two forms:

1. Console output examples (recommended for first time readers)
2. Self-checking examples in the form of JUnit tests

Content:

• Part One - Introduction
  
  1. Why Rx?
  2. Key types
  3. Subscription life cycle and
• Part Two - Sequences
  
  1. Creating a sequence
  2. Sequence filtering
  3. Study
  4. Aggregation
  5. Sequence transformation
• Part Three - Sequence Management
• Part Four - Parallelism

Part One - Intro: Why Rx?

Users expect real-time data. They want tweets now . Order confirmation now . They need prices as of now . As a developer, you need self-guided messages. You do not want to be blocked waiting for the result. You want the result to come to you in readiness. Moreover, you want to work with the result in parts: you do not want to wait until everything is loaded before displaying the first line. The world has switched to the notification mode. Developers have the tools to notify, it's easy. They need tools to respond to notifications.

Welcome to Rx. Rx is a powerful tool that allows you to solve problems in an elegant declarative style, inherent in functional programming. Rx has the following advantages:

• Intuitiveness
  
  • Actions in Rx are described in the same style as in other libraries inspired by functional programming, for example, Java Streams. Rx makes it possible to use functional transformations over event streams.
  
  
• Extensibility
  
  • RxJava can be extended with custom operators. And while Java does not allow this to be done in an elegant way, RxJava offers all the extensibility available in Rx implementations in any other language.
  
  
• Declarativity
  
  • Functional transformations are declared declaratively.
  
  
• Composability
  
  • Operators in Rx are easily assembled to perform complex operations.
  
  
• Convertibility
  
  • Operators in Rx can transform data types by filtering, processing, and expanding data streams as needed.
  
  

When should Rx be used?

Rx is used to compose and process sequences of events.

Rx should be used

• UI events such as mouse move, button click
• Events like property changes, collection updates, Order completed, Registration complete, etc.
• Infrastructure events (messages from the system, WMI or file managers)
• Integration with events from the message bus (message bus), messages from the WebScoket API
• Integration with CEP-systems (StreamInsight, StreamBas)

Rx use is possible

• Result of Future or Similar Pattern

Do not use Rx

• To turn Iterable into Observable, just to work with them through the Rx library.

In the next section, we will look at the fundamental types on which the concept of reactive programming is based: Observable and Observer.

Now the project has its own public repository and anyone can join the creation of an in-depth Russian-language tutorial on Rx. The translation of this part is already there, the rest will appear soon, and with your help, even faster.