If you have to add a library, do it normally with your tool (Maven) and then you also need to add them in IntelliJ. You can see an example here: https://medium.com/@authmane512/how-to-use-javamail-on-android-without-gradle-f61ec391a6fa

In fact, you have to add them in both tools.

Yes, you can avoid IntelliJ, but it’s hard. Before, I used Sublime Text, but the problem was that I didn’t have autocompletion ! As Java is very verbose, I had to tap a lot of text… IntelliJ is not so slow and give you a lot of useful tools, so I suggest to use it.