I have a swollen knee after playing basketball. but there is no pain whatsoever. it just feels liquidy (i.e: liquid is surrounding my knee and kneecap?

Effusion: You're describing a knee "effusion" or collection of fluid surrounding the knee joint. Effusions are the body's response to injury. Since you have no pain, the injury is probably minor. Best to rest it, elevate it and apply ice a few times a day for about 3 days. Once the swelling goes down, you can resume normal activities, but do so gradually. OTC Ibuprofen might help also. Best wishes.