Dagger component and module

gist.java

@Singleton
@Component (modules={UserModule.class})
public interface UserComponent {

    void inject(MainActivity activity);
}

@Module
public class UserModule {

    @Provides
    @Singleton
    UserService providesUserService() {
        return new UserServiceImpl();
    }
}

public interface UserService {

    String login();

    String logout();
}

public class UserServiceImpl implements UserService {

    public String login(){
        return "Logged in";
    }

    public String logout(){
        return "Logged out";
    }
}