dagger2-example | dagger2 with gradle example | Unit Testing library

I am trying to understand an example for an app with offline support using retrofit and room:

You can find the code for it here:

This project is using dependency injections with Dagger2. I've never worked with it so I am trying to understand how things work together. I understand the purpose of dependency injection but I don't understand the implementation of the project above.

I found a very good introduction into Dagger2 here:

A Friendly Introduction to Dagger 2

Dagger 2 example Code:

I worked through it and got most of it. Back to the actual project I am trying to understand (link 2). It still doesn't make sense to me and here is why:

1. The interface AppComponent has one method which is used: public void inject(MainActivity2ViewModel viewModelModule); The return type is void. In the Dagger2 sample project (link 3 and 4) they use WeatherReporter getWeatherReporter(); which makes sense because later they call this method to get a WeatherReporter-Instance and Dagger2 manages all of the instantation process in the background. But I get nothing if the return type is void. Why is the return type not an object?

2. There is one @Inject in MainActivity2ViewModel:

   @Inject public void setRepository(GitHubRepository2 repository) { this.repository = repository; }

repository is the only field of MainActivity2ViewModel so it is a dependency. The GitHubRepository2 constructor has 3 parameters: