Dear Mr Ovies,
Even a cursory knowledge of the J 31 vs the F 35 would suggest the similarities are only skin deep (or perhaps even not even that deep). There are two engines lurking in the J 31 for a start...
Thing is, current software design programs concerned with The Majik Of Stealth tend towards a certain similarity in terms of what a manned stealth aircraft looks like.
I'm not suggesting that elements of the J 31's design may not have been acquired through the normal industrial games present in our cruel and treacherous world, merely that the overall aim and direction of the Chinese program is quite different.