Andrew, you're correct of course hashing is a one-way operation with potential collisions
On Wed, Sep 21, 2016 at 3:22 PM, Andrew Duffy <r...@aduffy.org> wrote: > Pedantic note about hashCode and equals: the equality doesn't need to be > bidirectional, you just need to ensure that a.hashCode == b.hashCode when > a.equals(b), the bidirectional case is usually harder to satisfy due to > possibility of collisions. > > Good info: > http://www.programcreek.com/2011/07/java-equals-and-hashcode-contract/ > _____________________________ > From: Jakob Odersky <ja...@odersky.com> > Sent: Wednesday, September 21, 2016 15:12 > Subject: Re: What's the use of RangePartitioner.hashCode > To: WangJianfei <wangjianfe...@otcaix.iscas.ac.cn> > Cc: dev <dev@spark.apache.org> > > > > Hi, > It is used jointly with a custom implementation of the `equals` > method. In Scala, you can override the `equals` method to change the > behaviour of `==` comparison. On example of this would be to compare > classes based on their parameter values (i.e. what case classes do). > Partitioners aren't case classes however it makes sense to have a > value comparison between them (see RDD.subtract for an example) and > hence they redefine the equals method. > When redefining an equals method, it is good practice to also redefine > the hashCode method so that `a == b` iff `a.hashCode == b.hashCode` > (e.g. this is useful when your objects will be stored in a hash map). > You can learn more about redefining the equals method and hashcodes > here > https://www.safaribooksonline.com/library/view/scala-cookbook/9781449340292/ch04s16.html > > > regards, > --Jakob > > On Thu, Sep 15, 2016 at 6:17 PM, WangJianfei > <wangjianfe...@otcaix.iscas.ac.cn> wrote: >> who can give me an example of the use of RangePartitioner.hashCode, thank >> you! >> >> >> >> -- >> View this message in context: >> http://apache-spark-developers-list.1001551.n3.nabble.com/What-s-the-use-of-RangePartitioner-hashCode-tp18953.html >> Sent from the Apache Spark Developers List mailing list archive at >> Nabble.com. >> >> --------------------------------------------------------------------- >> To unsubscribe e-mail: dev-unsubscr...@spark.apache.org >> > > --------------------------------------------------------------------- > To unsubscribe e-mail: dev-unsubscr...@spark.apache.org > > > --------------------------------------------------------------------- To unsubscribe e-mail: dev-unsubscr...@spark.apache.org
