Dagger 2 injecting parameters of constructor

Question

I saw the following example on the Dagger 2 website:

class Thermosiphon implements Pump {
  private final Heater heater;

  @Inject
  Thermosiphon(Heater he         


        

Answer 1

For one, since you've annotated the constructor of Thermosiphon with @Inject, you don't need an @Provides method. Dagger uses this constructor to create an instance when needed. Just annotate the Thermosiphon class itself with @Singleton to preserve the singleton behavior.

If you do want to use an @Provides method, and to answer your question fully, you can specify the Heater as a parameter to the method:

@Module
public class ThermosiphonModule {

    @Provides
    @Singleton
    Thermosiphon provideThermosiphon(Heater heater) {
        return new Thermosiphon(heater);
    }

}