> Starting with the  fact that it returns a 32-bit *int* (and what happens
> when you have more  than 4 billion objects?  Possible in a 64-bit
> system!).

It's not an object-id, it's a hash code.  I.e. it does not guarantee that

     a != b  ==>  a.hashCode() != b.hashCode()

so the 32bit restriction is only a serious problem once the size of your
hashtable gets close to a billion of buckets.
Sure that can happen, but not nearly as soon as a 4GB Java process or even
a Java process with 4 billion objects.


        Stefan