Where do I find MainApplication.java in React Native (Expo)?

I'm trying to find the MainApplication.java file, so I can edit it. I'm using Expo Go.
I've been unable to find it. I've also used finder in Sublime Text comes with.
Nothing was found.

Where am I supposed to find it?

I am not sure it is doable with Expo as the aim is to develop a native code module outside the project.

I would recommend you to use React Native directly. See:

Setting up the development environment

You will have much more flexibility regarding native code source and if you need to change the configuration.

I'm on CLI but probably here:

android/app/src/main/java/com/{nameOfProject}/someFolder/MainApplication.java or android/app/src/main/java/co/{nameOfProject}/someFolder/MainApplication.java

Example path:
android/app/src/main/java/co/matt/rtp/MyAppPackage.java

If you're using Expo that's mean you using managed workflow.
You will not find MainApplication.java because expo took care of it.
You can do eject, it was changing the project from managed workflow to bare

Please check below references from expo

> The two approaches to building applications with Expo tools are called
> the managed and bare workflows.
>
> With the managed workflow you only write JavaScript/TypeScript and
> Expo tools and services take care of everything else for you. In the
> bare workflow you can use any Expo library and service, and you are
> responsible for the native iOS and Android projects.

https://docs.expo.dev/archive/managed-vs-bare/

In React Native projects created with Expo, there is no direct equivalent of the MainApplication.java file that you would typically find in a bare React Native project. Expo abstracts away the native code configuration, including the MainApplication.java file, to provide a streamlined development experience.

Expo manages the native code configuration for you, allowing you to focus primarily on the JavaScript code and leveraging Expo's pre-configured development environment. This abstraction makes it easier to develop and deploy React Native apps without dealing with native code setup and maintenance.

However, if you have specific native code requirements or need to customize certain aspects of your Expo project, you can "eject" your project from Expo to create a bare React Native project. After ejecting, you will have access to the native code files, including the MainApplication.java file.
Keep in mind that ejecting from Expo is a one-way operation, and it's recommended to do it only if necessary, as it adds complexity to the project setup and maintenance.

To eject an Expo project and obtain access to native code files, you can run the following command in your project's root directory:
expo eject
This command will guide you through the process of ejecting your project and generating the necessary native code files. Once ejected, you can find the MainApplication.java file in the appropriate location within the Android project structure, typically under the android/app/src/main/java/com/your-app-package/ directory.

Remember to carefully consider the implications of ejecting from Expo, as it may require additional configuration and maintenance on your part, including managing dependencies, integrating third-party libraries, and handling future updates to Expo.