Basically, the comparison with the F-22 seems to reveal a very different sort of role from the F-22 Lightning:

The J-20’s wing and control surface layout is very different from that of the Lockheed Martin F-22, but the body layout is quite similar, with twin main weapon bays under the belly and side bays for rail-launched air-to-air missiles (AAMs), all located under and outside the inlet ducts. On both aircraft, the main landing gear is housed in the fuselage behind the weapon bays and the engines are close together. The big difference, however, is that the J-20 is 9.5 ft. (17%) longer than the F-22, from the nose to the engine nozzles. Most of this is in the widest part of the fuselage, and since the weapon bays are similar in size, it is almost all available for fuel. It is a reasonable estimate that the J-20 could have as much as 40% more internal fuel capacity than the F-22. The longer body will also improve fineness ratio, with benefits for transonic drag.

Despite the larger body, the empty weight of the J-20 may be close to that of the F-22, largely because it has less-powerful engines without the heavy two-dimensional thrust-vectoring nozzles of the F-22’s F119s. The J-20 prototypes are believed to be flying with United Engine Corp. (UEC) AL-31F engines. The thrust difference between the two designs is very large: The F-22 has almost as much power in intermediate thrust as the J-20 does in full afterburner, although newer versions of the UEC AL-31/117S/117 could close the gap in later versions of the Chinese aircraft.

The conventional circular nozzles and the aft-body shape are less conducive to stealth than the F-22, as is the case with the T-50. This is most likely a conscious decision because a fast aircraft can tolerate a higher radar cross-section in the aft quadrant. While some observers have suggested that canards are incompatible with stealth, an engineer who was active in Lockheed Martin’s early Joint Strike Fighter efforts says the final quad-tail configuration was no stealthier than the earlier canard-delta design.

………

The J-20’s weapon arrangement is similar to the F-22, except that the ventral bays are shorter and narrower, and are apparently capable of accommodating only four weapons the size of the SD-10 AAM. However, they do appear large enough to accommodate bigger folding-wing missiles—and China is reported to be negotiating to buy the Russian Kh-58UShKE, a Mach 4 anti-radar missile that is also intended for internal carriage on the T-50.

The side missile bays differ from those of the F-22 in that the doors can be closed after the missile rail has been extended, and have been seen with a missile—or test shape—with low-aspect-ratio wings and folding tails. So far, no gun has been seen on J-20s, nor has there been a sign of provision for one.

The J-20 design, therefore, is an air-to-air fighter with an emphasis on forward-aspect stealth, efficient high-speed aerodynamics and range, with a modest internal payload and more than adequate agility for self-defense. The aircraft has considerable potential for development, because of its currently unsophisticated engines. But it is also large and expensive, and continued development of the J-10B shows that China plans to maintain a high-low mix of fighters for a long time to come.

The J-20’s weapon arrangement is similar to the F-22, except that the ventral bays are shorter and narrower, and are apparently capable of accommodating only four weapons the size of the SD-10 AAM. However, they do appear large enough to accommodate bigger folding-wing missiles—and China is reported to be negotiating to buy the Russian Kh-58UShKE, a Mach 4 anti-radar missile that is also intended for internal carriage on the T-50.

The side missile bays differ from those of the F-22 in that the doors can be closed after the missile rail has been extended, and have been seen with a missile—or test shape—with low-aspect-ratio wings and folding tails. So far, no gun has been seen on J-20s, nor has there been a sign of provision for one.

The J-20 design, therefore, is an air-to-air fighter with an emphasis on forward-aspect stealth, efficient high-speed aerodynamics and range, with a modest internal payload and more than adequate agility for self-defense. The aircraft has considerable potential for development, because of its currently unsophisticated engines. But it is also large and expensive, and continued development of the J-10B shows that China plans to maintain a high-low mix of fighters for a long time to come.

………

J-20 vs. F-22
	J-20	F-22
Overall length (ft.)	66.8	62
Wingspan (ft.)	44.2	44.5
Wing area (sq. ft.)	840	840
Operating empty weight (lb.)	42,750	43,340
Internal fuel (lb.)	25,000	18,000
Normal takeoff weight (lb.)	70,750	64,840
Max. thrust (lb.)	55,000	70,000
Min. thrust (lb.)	34,250	52,000
Clean-fuel fraction, normal T/O	0.35	0.28
Max. thrust-to-weight ratio, combat weight	0.94	1.25
Military thrust-to-weight ratio, combat weight	0.59	0.93
Wing loading at combat weight, lb./sq. ft.	69	66.5
Sources: Lockheed Martin, AW&ST analysis

Basically, the F-22 was designed to provide air supremacy by engaging in air to air combat over an enemy territory protected by an integrated Integrated Air Defense System (IADS).

It is essentially an offensive capability, where there bases relatively close to the battle space.

By contrast, the J-20 is less agile, it has about and less stealthy from the rear quarter, so it is intended to provide area denial, without a significant tankerbility, it has about 30% less installed thrust, and it carries about 40% more internal fuel.

Basically, it reflects a concern that the the US, operating from bases in places like Korea, Japan, and the Philippines, will launch an attack on China and near her allies, (I am thinking Myanmar might end up on the US’s “Axis of Evil”) and the presence of the capabilities of the J-20 would tend to really throw a monkey wrench into any planning.

Seeing as how China is developing the J-31 at the same time, which is roughly analogous to the F-35 (without all the excess baggage that the STO/VL capabilities of the B model), it would appear that the J-20 is directed very specifically toward US adventurism.

As such, I would not expect that they would make a whole bunch of these aircraft.

A few dozen would suffice to provide sufficient deterrence,