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
