RxJava 2.0 was released not so long ago (in November 2016), so not all libraries have had a chance to catch up and migrate to a new version.

Often, it is rather difficult to update a library to RxJava 2.0, as it means that the old API will have to be broken and that's not always acceptable.

However, as we will see in the next chapter, there can be lots of cases for a developer to use a library that hasn't migrated to RxJava 2.0 and the main code base is still written in RxJava 1.0. In such circumstances, a very good solution is to use the available compatibility layers or to create your own.
This might not be the most exciting chapter in the book, but it will definitely come in handy for Android developers as lots of libraries are still using RxJava 1.0.
The topics covered in this chapter are as follows:

• What are the differences between RxJava 1.0 and RxJava 2.0?
• How to set up interoperability libraries
• How to convert version 1 Observables to version 2