Question

Suppose I have the following base class, Queen and Knight as its derivatives. WeaponBehaviour is an interface. I can’t figure out how to inject weapons using Guice depending on the concrete GameCharacter type.

public abstract class GameCharacter {
    @Inject
    protected WeaponBehaviour weapon;

    public GameCharacter() {

    }

    public void fight() {
        weapon.useWeapon();
    }

    public void setWeapon(WeaponBehaviour weapon) {
        this.weapon = weapon;
    }
}

Answer 1

You could use Binding Annotations.

A subclass:

class GimliSonOfGloin extends GameCharacter {

    @Inject
    public void setWeapon(@Axe WeaponBehaviour weapon) {
        super.setWeapon(weapon);
    }
}

The Annotation:

@BindingAnnotation 
@Target({ FIELD, PARAMETER, METHOD }) 
@Retention(RUNTIME)
public @interface Axe {}

The Binding:

bind(WeaponBehaviour.class)
    .annotatedWith(Axe.class)
    .to(MyAxe.class);