How to inject with Guice when there are two different constructors?

Question

Total Guice noob here, have read a few articles and seen the intro video, that's about it.

Here's my simplified old code that I'm trying to "guicifiy". Can't quite figure out how to, since (as far as I understand), I can only @inject-annotate one of the two constructors? How can a calling class create the one or the other instance? Or will I have to refactor this somehow?

public class MyDialog extends JDialog {
    public MyDialog( JFrame parent, <other parameters...> ) {
        super( parent );
    }

    public MyDialog( JDialog parent, <other parameters...>) {
        super( parent );
    }
 }

Answer 1

You can only inject into the one ctor.

Depending on how this class is being used, you could:

• Inject a factory into the client code with two "new" methods.
• Roll all the arguments into one ctor and pass null when not required.

How can a calling class create the one or the other instance?

This suggests that the calling classes will want multiple instances of MyDialog? Then you need to use a hand-rolled factory (Assisted Inject can handle this for you if you only had one ctor). I don't know the details of what you are up to and I'm likely repeating what you already know but as a blanked statement I'd suggest also extracting an interface from MyDialog and have the factory return them. This way you can fake MyDialog in tests.

Answer 2

Constructor injection is very clean. mlk is right, saying that you can inject into one constructor only.

What you can do is use method injection:

public class Smt {

    private int a;
    private Cereal cereal;
    private Personality personality;
    private ignition;

    public Smt() {
        this.a = 5;
    }

    public Smt(int a) {
        this.a = a;
    }

    @Inject
    public void setup(@CiniMini Cereal cereal, @Rastafarian Personality personality,
        Ignition ignition) {
        this.cereal = cereal;
        this.personality = personality;
        this.ignition = ignition;
    }
}

What Guice will do is call your class' setup class method and provide all the injections. Then you do the same thing as in the constructor--assign the objects to your class' attributes.