Considering the fact that the devices hit the shelves more than a year ago — June 2018 — they should have been updated to Android 9.0 long ago, not weeks before the unveiling of Android Q.
Still, it’s a welcome change for the phones’ users, as they’ll finally get to enjoy Samsung most refined UI till date — One UI.
The updates — software version PPR1.180610.011.J337VVRU3BSEB on J3 and PPR1.180610.011.J337VPPVRU3BSEB on J3 V, respectively — carry the June 1st security patch level alongside the usual Android Pie goodness.
As these are OTA updates, it could take a while for your device to get the update automatically. To initiate it manually, go to Settings > About phone > Software updates > Check for Updates.