According to Gongke in CJDBY (he seems to be a reliable insider there), at current configuration, J-20's empty weight is less than Su-27.
And according to Pupu (who is a quite reliable source), the current J-20 has the highest thrust/weight ratio among all PLA fighters in service, which sidely proved Gongke's claim.
Which means, J-20's empty weight should not be more than 16 ton, which is considerably lighter than F-22's 19.7 ton and slightly higher than F-35's 13.5 ton.
About a year ago, Sina has published an article on the innovation of J-20's manufacturing process, include the intensive usage of advanced process and 3d-printing to reduce structural weight yet maintain structural strength, and advanced stealth coating tech could be another reason why J-20 is so light-weighted.
Due to J-20's optimization at super-sonic, some source claimed even with AL-31F, J-20 can reach Mach-1.5 without afterburner, but the time takes it to that speed are not satisfy super-cruise standard, but still, quite an achievement. Thanks to the J-20 aerodynamic design, actually the ratio of supersonic resistance (sorry don't know the term in English) for J-20 is just 70% of Su-27, no wonder the PLAAF J-20 pilot say when it comes to supersonic range, no one can match the performance of it.
No wonder PLAAF chief openly praised J-20 (the only PLA equipment received such honor) and rush to mass production of J-20 even without target engine.