How to initialize a circular dependency (final fields referencing each other)?

Question

How do you initialize this:

class A {
    final B b;

    A(B b) {
        this.b = b;
    }
}

class B {
    final A a;

    B(A a) {
        this.a = a;
           


        

Answer 1

What you are having is a circular dependency. The only way I can think of is to not declare the fields as final and have your dependency injected using setter injection instead of constructor injection.

A a = new A();
B b = new B();

a.setB(b);
b.setA(a);