Mastering Reactive Android programming with RxJava is no easy feat. At first, the way the code is structured and written may seem strange and alien. However, with some practice, we will quickly see that it is an easy and understandable way to write concurrent and parallel code.

One of the best ways to learn is by example. That's why we will build a simple application to learn RxJava. It will be a very straightforward financial stock quote monitoring app. We will tap into the streams of Yahoo Finance data to display the quotes while using the basics of RxJava.

In the later stages, we will plug in an endless stream of Twitter data and we will start using more advanced techniques to transform and handle data.
First of all, we will start with a simple Hello World application that will provide a solid foundation to the all the things that we will learn.
By the end of this chapter, we will learn and do the following things:

• Create an initial barebone for the application
• Set up RxJava and UI dependencies
• Create an initial UI where we will show the stock quote updates
• Initialize UI with mock data using RxJava to get a Hello World screen