It can be legitimate, especially in the case of Object.hashCode(), but it's supposed to be in sync with equals() by contract. As it stands, two objects which are equal() will produce different hashes, or the same logical object will produce different hashes across JVMs. That breaks the contract.. if the equals() method simply did return (other == this), then it'd be fine, albeit a little useless.
I created an issue and posted a 1-liner patch that would eliminate the problem by using getClass().getName().hashCode() to incorporate type information into the hashCode without depending on a Descriptor object's memory address. On May 11, 12:01 am, Dmitriy Ryaboy <[email protected]> wrote: > Hi Jay, > > I encountered that before. Unfortunately this is a legitimate thing to > do, as documented in Object.hashCode() > > I have a write-up of the problem and how we wound up solving it (not > elegant.. suggestions welcome) > here:http://squarecog.wordpress.com/2011/02/20/hadoop-requires-stable-hash... > > D > > > > > > > > On Mon, May 9, 2011 at 8:25 AM, Jay Booth <[email protected]> wrote: > > I'm testing an on-disk hashtable with Protobufs and noticed that with > > the java generated hashcode function, it seems to return a different > > hashcode across JVM invocations for the same logically equivalent > > object (tested with a single string protobuf, same string for both > > instances). > > > Is this known behavior? Bit busy right now backporting this to work > > with String keys instead but I could provide a bit of command line > > code that demonstrates the issue when I get a chance. > > > Glancing at the generated hashcode() function, it looks like the > > difference comes from etiher getDescriptorForType().hashCode() or > > getUnknownFields().hashCode(), both of which are incorporated. > > > -- > > You received this message because you are subscribed to the Google Groups > > "Protocol Buffers" group. > > To post to this group, send email to [email protected]. > > To unsubscribe from this group, send email to > > [email protected]. > > For more options, visit this group > > athttp://groups.google.com/group/protobuf?hl=en. -- You received this message because you are subscribed to the Google Groups "Protocol Buffers" group. To post to this group, send email to [email protected]. To unsubscribe from this group, send email to [email protected]. For more options, visit this group at http://groups.google.com/group/protobuf?hl=en.
