Well, China's J-20 stealth fighter plane isn't so 'secret' anymore. Although there is so speculation as to what role the jet will play within the Chinese military, it is known that the J-20 is very advanced. It is most closely associated with, or compared rather, to the U.S F-22. The F-22 is a highly maneuverable aircraft capable of speeds of Mach 1.8, or 1369.8 miles per hour!
However, the J-20 isn't planned to be introduced until about 2017, several years from now. China is capable of designing new weapons and aircrafts with the help of it's booming economy. Recently the U.S announced plans to introduce the F-35, a new jet that could potentially replace the F-22. All in all, the 3 jets are very advanced fighting machines.