Hi, > On 8 Dec 2017, at 11:12, Thomas Mortagne <[email protected]> wrote: > > Hi devs, > > Most Object#hashCode() are implemented using HashCodeBuilder. > HashCodeBuilder provide an empty constructor and also allow setting > "random" numbers. > > http://dev.xwiki.org/xwiki/bin/view/Community/JavaCodeStyle#HEquals2FHashCodeandToStringimplementations > does not really say anything about what do do and when currently so I > would like to have a clear rule about it. > > On my side when I don't plan to use different types of objects in a > hash key I usually simply use the empty HashCodeBuilder constructor. > The only point of setting different numbers is when you might end up > comparing different object types (and even in that case you have the > #equals() safeguard anyway so it's mostly about performances in > practice). > > So here is a proposal: it's OK to use empty HashCodeBuilder constructor > except: > * when overwriting the hachCode of a super class you should use > different numbers than the super class (since there is big chance to > have that super class used as a hash key) > * as a best effect in general if you know that you are going to have > several different types as hash key, try to make sure they use > different random numbers, your proc will thank you :) > > WDYT ?
I don’t fully master the topic but I’m trusting you so +0 from me. Only comment is that it means there’s not a single way of writing our code and thus is not that easy to check. Thanks -Vincent > > -- > Thomas Mortagne
