Question

Lets say I have a Outer class. Lets say there is a non static member class Inner. So an Outer instance will have a reference to an instance of Inner if the Outer class declares a field of type Inner and that is by definition. But how does Inner instance also has a implicit reference to Outer? When is this association created?

Answer 1

From the Java language Spec

An instance i of a direct inner class C of a class O is associated
with an instance of O, known as the immediately enclosing instance of
i. The immediately enclosing instance of an object, if any, is
determined when the object is created (§15.9.2).