HOWTO override module in dagger2

0_BaseActivityComponent.java

public interface BaseActivityComponent {
  
}

1_BusModule.java

@Module
public class BusModule {
  @Provides
  @PerActivity
  public Bus provideBus() {
    return new AsyncBus();
  }
}

2_DebugBusModule.java

@Module
public class DebugBusModule {
  @Provides 
  @PerActivity
  public Bus provideBus() {
    return new DebugBus();
  }
}

3_ActivityComponent.java

@PerActivity
@Component(modules = { ActivityModule.class, BusModule.class }, dependencies = AppComponent.class)
public interface ActivityComponent extends BaseActivityComponent{
  void inject(MainActivity activity);
}

4_DebugActivityComponent.java

@PerActivity
@Component(modules = { ActivityModule.class, DebugBusModule.class }, dependencies = AppComponent.class)
public interface DebugActivityComponent extends BaseActivityComponent {
  void inject(DebugActivity activity);
}

5_BaseActivity.java

public abstract class BaseActivity extends Activity {
  private BaseActivityComponent component;

  @Override protected void onCreate(Bundle state) {
    super.onCreate(savedInstanceState);
    this.component = createComponent();
  }

  public BaseActivityComponent getComponent() {
    return component;
  }

  protected BaseActivityComponent createComponent() {
    MyApp app = (MyApp) getApplication();
    return DaggerActivityComponent.builder()
          .appComponent(app.getComponent())
          .activityModule(new ActivityModule(this))
          .build();
  }
}

6_DebugActivity.java

public class DebugActivity extends BaseActivity {
  @Inject
  Bus bus; // после вызова inject() в onCreate сюда встанет DebugBus
  
  // мы переопределяем createComponent от базового класса
  // и в onCreate базового класса вызовется этот метод
  @Override
  protected BaseActivityComponent createComponent() {
    MyApp app = (MyApp) getApplication();
    return DaggerDebugActivityComponent.builder()
              .appComponent(app.getComponent())
              .activityModule(new ActivityModule(this))
              .build();
  }

  @Override
  protected void onCreate(Bundle state) {
    super.onCreate(state);
    setContentView(R.layout.activity_debug);
    ((DebugActivityComponent) getComponent()).inject(this);
  }
}