I don't know whether or not I have ADHD?

I'm 21 years old and ever since I can remember I have struggling with controlling my anger. I am not a very emotional person, anger is the only thing I can do well to be honest. Most negative emotions I can only deal with by being angry, if I'm upset I won't necessarily feel upset ill be more angry. I feel like I'm angry all the time, absolutely anything can fire me into a foul mood and I feel I have to struggle to remain calm and polite. A friend noticed this and suggested it could be ADHD but I don't know enough about it to know what it is. Has anyone got any suggestions?