[jira] [Closed] (KYLIN-4327) TOPN Comparator may violate its general contract

["Xiaoxiang Yu (Jira)" <ji...@apache.org>]

     [ https://issues.apache.org/jira/browse/KYLIN-4327?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel ]

Xiaoxiang Yu closed KYLIN-4327.
-------------------------------

Resolved in release 3.1.0 (2020-07-03)

> TOPN Comparator may  violate its general contract
> -------------------------------------------------
>
>                 Key: KYLIN-4327
>                 URL: https://issues.apache.org/jira/browse/KYLIN-4327
>             Project: Kylin
>          Issue Type: Improvement
>            Reporter: Yifei Wu
>            Assignee: Yifei Wu
>            Priority: Minor
>             Fix For: v3.1.0, v3.0.1
>
>
> in current TopN， it  should save top(k) result and keep it in double value, just like this:
> ```
> public class Counter<T> implements Serializable{
>     ...
>     protected T item;
>     protected double count;
>     ...
> }
> ```
> But its Comparator method use  "=="  directly to compare the result, it may cause the error  "*violate its general contract*" when calling it.
> ```
>           private static final Comparator ASC_COMPARATOR = new Comparator<Counter>() {
>         @Override
>         public int compare(Counter o1, Counter o2) {
>             return o1.getCount() > o2.getCount() ? 1 : o1.getCount() == o2.getCount() ? 0 : -1;
>         }
>     };
> ```



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