Github user tarekauel commented on the pull request:
https://github.com/apache/spark/pull/6981#issuecomment-116881285
@Davies
To be honest, I don't think that this is precise enough, is it? Someday
someone will create a Jira ticket and report the "bug" below:
```
scala> 1970 + ((new
java.text.SimpleDateFormat("yyyy-MM-dd").parse("2015-01-01").getTime - 1)/ 1000
/ 3600 / 24 / 365.24).toInt
res1: Int = 2015
```
```
scala> val c = java.util.Calendar.getInstance(); c.setTimeInMillis(new
java.text.SimpleDateFormat("yyyy-MM-dd").parse("2015-01-01").getTime - 1)
scala> c.get(java.util.Calendar.YEAR)
res6: Int = 2014
```
I changed the coding in order to use `java.util.Calendar`. I compared the
runtime for calculating the month 1,000,000 times:
`sdf 1791ms`
`calendar 251ms`
This is significant faster.
I created in a small prototype a custom implementation (without any Date
functions and it was just as fast as `Calendar`
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