public abstract class CarApplication

The entry point an app implements to provide its in-car (Apple CarPlay / Google Android Auto) experience. Register a single instance with Car#setApplication(CarApplication) from your app’s init() so it is in place before a head unit connects:

public void init(Object ctx) {
    // ... normal app init ...
    Car.setApplication(new MyCarApplication());
}

class MyCarApplication extends CarApplication {
    public CarScreen onCreateRootScreen(CarContext context) {
        return new LibraryScreen();
    }
}

Referencing any com.codename1.car type is what tells the build to wire the native in-car support (CarPlay scene + entitlement, Android Auto CarAppService + dependency); apps that never touch the package pay nothing. The app must also be in a head-unit-eligible category and declare it via build hints (see the category hints in the developer guide).