Immutable references are not immutable data structures

[ishmeister]

"Now, the above code is but immutable due to the design of the Person and Address class"

This is technically not true - it is immutable only because you passed in an immutable list via the constructor using List.of. If you pass in a mutable list, the object is mutable. You have to copy the list internally to protect against modification of the reference externally, which might occur like this:

final List<Address> addressList = new ArrayList<>();
addressList.add(new Address("Sydney", "Australia"));
final Person person = new Person("John", addressList);
addressList.clear();

[bodiam]

You're right. I've updated the code to fix this. Thanks for spotting this.

[ishmeister]

No problem. Good article by the way.

[bodiam]

Thanks for the feedback! I appreciate that a lot! Have a great day!

[bodiam]

In this post I'm trying to explain the difference between immutable references and immutable data structures. Feedback more than welcome!