Re: The World's 4th,4.5 & 5th Generation Fighters
1) Maybe the development of the J-20 had been more completed and advance than all of us had thought. And that this was not the first maiden flight.
2) The Chinese might wanted to forfeit certain tests that was normally in the procedure before reaching production.
As to what the CHinese mean about "Situation becomes urgent", might mean that the Chinese felt that their sovereignty being challenged and that the situation with any nations had deteriorate very far down. Also that potential very hostile nations are fielding more credible weaponries.
However all these situation would most likely developed into an arm race which I personally hope will never come to past.
"Situation becomes urgent" I can only foresee the under circumstances:
1) The Japanese got the F-35 in which the USAF 'recommends' Japan getting 40 plus. Thus to maintain its air projection, PLAAF speed up its deployment of J-20s.
2) Indian and Russian joint project on PAK 50 and Indian Air Force orders the deployment in 5 years down the road. To maintain the stabilty of the borders of West China, PLAAF needs the deployment fast.
3) Even if India doesnt get her PAK 50, Japan doesnt get her F-35s, sooner or later Taiwan Air Force will procurment of newer 'stealth-like' fighters like F-15SE or the 4th gen Mirage 2000. This will also force the PLAAF to deploy the J-20s early.
Together with J-20s, J-16, DF21D anti-ship missile and the still mysterious 4th gen heavy bomber rumoured to be H8 or H9, PLAAF could well be the force to be reckon with for the next 10 years or so. From these situations, if budget permits PLAAF could also come up with a few more stealth aircraft projects.
Modern warfare has a whole new defination such that the word 'WAR' doesnt limit to war time but in peace times, these high tech cutting age weapons ''are already fighting'' their imaginery foes.