Hi Piyush, I thought I had it right this time! The Factory.hashCode algorithm multiplies by 31 for each loop, so I assumed it would be fully discriminating. I've even added several unit test cases checking this (see CookieTestCase class).
Now, looking closer, it appears that we indeed could run into some very very rare cases where two unequals objects could return the same code. I guess we can't affort them, even if there is one chance over a Integer.MAX_VALUE! So I'll have to reverse the equals() implementations to manual comparison of each property :( Best regards, Jerome > -----Message d'origine----- > De : Piyush Purang [mailto:[EMAIL PROTECTED] > Envoyé : mercredi 15 novembre 2006 22:40 > À : [email protected] > Objet : equals and hashcode > > Hi Jerome, > > I saw the implementation of equals for cookie and have to admit I was > almost shocked :) > > The code brings out to the fore the following phrases/sentences from > the Object#equals and hashcode contracts > > Object#equals > 1.1 equals method for class Object implements the most discriminating > possible equivalence relation on objects > > 1.2 so as to maintain the general contract for the hashCode method, > which states that equal objects must have equal hash codes. > > Object#hashCode > > 2.1 It is not required that if two objects are unequal according to > the equals(java.lang.Object) method, then calling the hashCode method > on each of the two objects must produce distinct integer results > > > the essence of my objection to the present implementation is that > "equal objects must have equal hash codes" but not "objects having > equal hashCodes must be equal" > > In cookies case an example might be contrivied where for one cookie > the version is say 1, name evaluates to 2 and all others evaluate to 1 > and for another cookie the version is 2, name evaluates to 1 as do the > other params .. in this case equals as implemented by Cookie will lead > to a faulty conclusion of "true". The equals has to be even more > discriminating than hashCode. and the instanceOf doesn't make it > discriminating enough. > > I hope I was succint enough. > > Cheers > Piyush
