Call constructor within constructor with self(this)-parameter

Question

I need to link an object of type B to any instance of type A (circular dependencies). I could also declare another method, which must be called after the constructor of A and link a new B to an A-instance. What I want to achieve is not having to call such a method manually. This is the sample code:

public Class A{
    B b;
    public A(){
        b = new B(this); // this does not work,
                         // as this references an object that has not been created yet
    }
}

public Class B{
    A a;
    public B(A a){
        this.a = a; //or something else
    }
}

I commented the problematic line. I also understand why it can't work. What I need to know is, if there is a well-known design pattern to avoid this problematic? Or should I just redesign my class model, putting anything in B to A? Any suggestions?

Answer 1

It does work. It's problematic in that it exposes an object before it's been fully initialized (so if the B constructor calls methods on the parameter, for example, that could be a bad thing), but it does work. The reference B.a will be a reference to the instance of A that's been/being constructed.

I would recommend trying to avoid the cyclic reference where possible, but where the alternative is even worse, the code you've given will work.