The 17 ton J-8 is a Chinese redesign of the MiG-21, giving it two engines and a slightly different shape. This did not work out as well as the Chinese expected. The aircraft entered service in the 1980s and has been upgraded with better electronics. Its basically a J-7 with longer range, larger payload and more resistant to damage (from being larger and having two engines.) J-8s can be used for bombing, although it can only carry about two tons of weapons. There are over 400 J-8s in service.
Meanwhile, production of J-10 (a Chinese design using Israeli and American technology) and the J-11 (licensed copy of the Russian Su-27/30) has been accelerated. In the next few years, China appears headed for a fighter force of 600 late model J-7s, 500 J-8s, a hundred or so J-10s and 300 or more J-11s. One reason for Chinese pressure on the European Union to drop the arms embargo is so the J-7s and J-8s can be equipped with the most modern European electronics.
The Chinese air force is accelerating its modernization program. The Chinese air force has, a year ahead of schedule, withdrawn the J-6 (a copy of the Russian 1950s MiG-19) from service. Several air force divisions were disbanded in the process. This makes the J-7 (a Mig-21 copy) the oldest fighter in Chinese service. This is a small aircraft, nine tons max, but has been greatly upgraded over the last two decades. Most of the older J-7B models are gone, replaced by J-7E and J-7G models. These models have better engines, maneuverability and electronics. With modern air-to-air missiles, these J-7s can be quite lethal. However, the small J-7s cannot carry much fuel or many missiles (usually on two are carried). This means that you pay a very high price, to train competent pilots, to fly a short range aircraft without much firepower. There are over 600 J-7s in service.