Can Spark Dataframes preserve order when joining?

[Jestin Ma]

If it’s not too much trouble, could I get some pointers/help on this? (see link)
http://stackoverflow.com/questions/38085801/can-dataframe-joins-in-spark-preserve-order
 
<http://stackoverflow.com/questions/38085801/can-dataframe-joins-in-spark-preserve-order>

-also, as a side question, do Dataframes support easy reordering of columns?

Thank you!
Jestin