I'm going to barium enema next week with that I have black stools and blood black and sometimes red stools. What are the complications of examination?

Not many. However I don't believe given your symptoms that this is the most appropriate test. A colonoscopy and possible upper endoscopy will be more accurate, more comfortable and possibly therapeutic. See a GI doctor to get confirmation before putting yourself thru an inadequate exam that may not provide you the answer you are looking for.
Usually safe. Barium enema is a safe exam with experienced technicians. It was a very common test before colonoscopy became more popular. Your doctor wants to know if there is a mass in your colon causing bleeding. With black stools I would have recommended an upper endoscopy and colonoscopy same time. Your doctor may have a reason to to barium enema.
Why a BE? Barium enemas have few complications but have largelly been replaced by colonoscopy for work-up of gastrointestinal bleeding. Unless you are in a very rural area with no access, I would ask my doc why the be instead of colonoscopy. Also in a 22 year old, black stools are more likely due to duodenal ulcers and gastritis than colon cancer - perhaps an egd to look in your stomach?

Related Questions

I'm going to barium enema next week with that I have black stools and blood black and sometimes black stools. What are the complications of examination?

Few. Serious complications from a barium colon study are rare. Very rare cases of perforation of the rectum have been reported during insertion of the enema tip. Adequate lubrication and gentle insertion are the best prevention. Minor side effects include bloating, cramping, and passing gas.