You are a nonresident for the year of 2017.
When you were on a F-1 visa, you are considered as a nonresident up to five years ( 2008-2012). However, with changing to a J-visa, the "lookback rule" applies, which you are considered as exempt in both 2011 and 2017. Please see example 9 under IRS example
Starting from January 1, 2018, you will start count your days when being present in the US. You will file a 2018 Form 1040 as a US resident for tax purposes if meet the Substantial Presence Test SPT.
[Edited 2/4/2018 5:40PM]
