Any nice way to make two immutable objects refer to eachother?

Question

Take these two Java classes:

class User {
   final Inventory inventory;
   User (Inventory inv) {
       inventory = inv;
   }
}

class Inventory {
   final User         


        

Answer 1

Slightly pedantic, but it's not strictly speaking necessary to create one inside the other, if you don't mind a little indirection. They could both be inner classes.

public class BadlyNamedClass {
    private final User owner;
    private final Inventory inventory;

    public BadlyNamedClass() {
        this.owner = new User() {
            ... has access to BadlyNamedClass.this.inventory;
        };
        this.inventory = new Inventory() {
            ... has access to BadlyNamedClass.this.owner;
        };
    }
    ...
}

Or even:

public class BadlyNamedClass {
    private final User owner;
    private final Inventory inventory;

    public BadlyNamedClass() {
        this.owner = new User(this);
        this.inventory = new Inventory(this);
    }
    public User getOwner() { return owner; }
    public Inventory getInventory() { return inventory; }
    ...
}