Dagger 2 injecting parameters of constructor

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If you’re using modules, then if you have two provider modules bound to the same component, then you’ll be able to allow them to see the heater as a constructor parameter.

@Module
public class HeaterModule {
    @Provides
    @Singleton
    Heater heater() {
        return new Heater(); // if not using @Inject constructor
    }
}

@Module
public class ThermosiphonModule {
    @Provides
    @Singleton
    Thermosiphon thermosiphon(Heater heater) {
        return new Thermosiphon(heater); // if not using @Inject constructor
    }
}

@Singleton
@Component(modules={ThermosiphonModule.class, HeaterModule.class})
public interface SingletonComponent {
    Thermosiphon thermosiphon();
    Heater heater();

    void inject(Something something);
}

public class CustomApplication extends Application {
    private SingletonComponent singletonComponent;

    @Override
    public void onCreate() {
        super.onCreate();
        this.singletonComponent = DaggerSingletonComponent.builder().build(); //.create();
    }

    public SingletonComponent getSingletonComponent() {
        return singletonComponent;
    }
}

But with constructor injection, you will also be able to provide objects of that given scope, or unscoped objects, as long as they have a @Inject constructor.

For example,

@Singleton
@Component // no modules
public interface SingletonComponent {
    Thermosiphon thermosiphon();
    Heater heater();

    void inject(Something something);
}

And

@Singleton
public class Heater {
    @Inject
    public Heater() {
    }
}

And

@Singleton
public class Thermosiphon {
    private Heater heater;

    @Inject
    public Thermosiphon(Heater heater) {
        this.heater = heater;
    }
}

Or

@Singleton
public class Thermosiphon {
    @Inject
    Heater heater;

    @Inject
    public Thermosiphon() {
    }
}

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