you can see Storm's builtin operation Count:
https://github.com/apache/storm/blob/b2a8a77c3b307137527c706d0cd7635a6afe25bf/storm-core/src/jvm/storm/trident/operation/builtin/Count.java
it return the new object:
@Override
public Long combine(Long val1, Long val2) {
return val1 + val2;
}
2014-10-24
shengyi.pan
发件人："Delm Schmidt" <d...@gmx.net>
发送时间：2014-10-23 21:58
主题：Implement the CombinerAggregator
收件人："user"<user@storm.apache.org>
抄送：
Hi guys,
maybe someone can help me out.
I'm trying to write my own CombinerAggregator. Hence I'm extending the
CombinerAggregator<T> Interface but I do not know how to efficiently implement
the 'T combine(T val1, T val2)' method.
Is it allowed to modify the val1 attribute and then return it or should I
create a new object and combine the values inside the newly created one?
