RFR: 8027470: AnnotationSupport uses == rather than .equals to compare Class objects

John Rose john.r.rose at oracle.com
Fri Nov 15 21:04:32 UTC 2013

On Nov 14, 2013, at 7:21 PM, Joseph Darcy <joe.darcy at oracle.com> wrote:

> Catching up on email, the specification of java.lang.Class does not explicitly promise that its notion of equality must be identity for all time. Therefore, while not required for today's implementations, I would prefer that new code we write in the JDK use equals rather than == when comparing classes.

There's no possible future where java.lang.Class would return true for equals but false for == (acmp).  So there's no future-proofing to do here.

Reification of generics might require something like this, but we could not break class identity without (as others have pointed out) breaking compatibility with a huge amount of code "in the wild".

Before that would happen, we would introduce a new auxiliary type (e.g., java.lang.Species and java.lang.Object::getSpecies) that would represent the richer view of an object's runtime type.

I do hope, in a future release, to "hack" reference equality, but in a different direction, allowing == (acmp) to return true *more often*, not allowing it to return *less often*.  The point will be to align the semantics of equals and acmp *more* closely for some types, notably the wrappers and java.lang.String.  (Interned referneces are so last-century.)

— John

More information about the core-libs-dev mailing list