MainActivity.java

public class MainActivity extends AppCompatActivity {

    @Inject
    DataManager mDataManager;
  
  
   @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);

        DaggerActivityComponent.builder()
                    .activityModule(new ActivityModule(this))
                    .applicationComponent(DemoApplication.get(this).getComponent())
                    .build().inject(this);

    }
}