Question

I have a simple hierarchy like follows:

public abstract class AbsFoo {
    protected AbsBoo boo;
}

public class Foo extends AbsFoo {
    public Foo() {
        boo = new Boo(); // Boo extends AbsBoo
    }
} 

EDIT: Instances of AbsFoo should be created on the fly and may not be fields

Can I replace boo = new Boo() with injection?

Answer 1

Yes:

public abstract class AbsFoo {
    protected AbsBoo boo;
}

public class Foo extends AbsFoo {
    @Inject
    public Foo(Boo boo) {
        super.boo = boo; // Boo extends AbsBoo
    }
} 

Make sure you construct your Foo instance with @Inject or injector.getInstance()

Edit

You can also use a provider to create instances on demand:

@Inject
Provider<Foo> fooProvider

//...

public void doSomething(){
    //need new foo:
    Foo foo = fooProvider.get();
}