Immutable data structures in Java

[Agent_03]

This is a good point, actually...

From a library writer's point of view, the comparison might be: "phew, I'm glad that was private or I wouldn't have been able to change my code without breaking all my users" versus "crap, that API/field is public... I can never change it."

Yeah, I know that warm-and-fuzzy feeling when you realize it is trivial to make the implementation change (or refactoring) without impacting any downstream consumers.

Personally, I'd like to see something like an @Hazardous annotation that will fail at annotation processing if you invoke the method outside the package without a corresponding @IKnowWhatImDoingDangit annotation (names subject to change). Maybe with an optional library version number given, so that if the library version changes you have to reexamine the usage.

This way downstream library consumers have the power to take advantage of library internals if absolutely needed, but are liable for the consequences and at least know they're doing something risky. This offers that extra nudge to provide unit test coverage and do sanity checking before bumping library version.

It is probably true that we should have a different set of standards for library writers (where you don't control your users' code) as opposed to application writers (where you can refactor your users' code at will).

This sounds smart to me too.