Records: supertype?

Tagir Valeev amaembo at
Wed Jun 12 04:57:21 UTC 2019

While java.lang is the most obvious place to put the new base class, it's
not the only possibility. I think such bad class is not very important to
import it by default. It could be placed in separate package like
java.lang.record to avoid any name clash with existing code.

With best regards,
Tagir Valeev

ср, 12 июня 2019 г., 2:41 Brian Goetz <brian.goetz at>:

> We've gone back and forth a few times on whether records should have a
> special supertype, as enums do (java.lang.Enum.)
> Enums benefit from having an explicit supertype for a number of reasons:
>   - It provides a type bound that is useful in API signatures (e.g.,
> EnumSet<E extends Enum<E>>);
>   - The base class actually has state;
>   - It provides declarations of public methods such as `ordinal()`,
> `compareTo()`, and `getDeclaringClass()`, and implementations of methods
> such as `toString()` and `readObject()`;
>   - It declares supertypes such as `Comparable`;
>   - It provides a place to capture specification of enum-specific
> behavior, in a way that is more discoverable within the IDE than putting
> it in the JLS.
> One could make the same argument that records should similarly have an
> explicit supertype (e.g., `AbstractRecord`), but the arguments aren't as
> decisive:
>   - No state in the base class;
>   - No record-specific methods or supertypes (currently);
>   - Hard to imagine `<T extends AbstractRecord<T>>` showing up in APIs,
> though it's possible.
> Which is to say, the choice of whether or not to have a base class for
> records is less obvious.  Still:
>   - The specification for equals/toString/hashCode for records is
> somewhat refined over that of Object, and putting it in the Javadoc is
> the sensible place to put it;
>   - One can imagine wanting to add methods like `toJson()` to records in
> the future, and an abstract base class is a sensible place to put it.
> So, one could make a case for "do the simplest thing" (no supertype),
> or, alternately, be more like enums, and still get some benefits.
> If we decide to go for the supertype, there's a bikeshed to paint.
> Record is the obvious analogue to Enum, but I worry that it will create
> clashes with user code (java.lang names are always auto-imported.)
> AbstractRecord feels a little clunky.  (Once you've weighed in on the
> first question, you can proceed to the bikeshed.)
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